BMJ Open€¦ · Benjawan Tawatsupa, The Australian National University Building 62 – NCEPH,...
Transcript of BMJ Open€¦ · Benjawan Tawatsupa, The Australian National University Building 62 – NCEPH,...
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Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults
Journal: BMJ Open
Manuscript ID: bmjopen-2012-001396
Article Type: Research
Date Submitted by the Author: 30-Apr-2012
Complete List of Authors: Tawatsupa, Benjawan; Health Impact Assessment Division, Department of Health; National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology and Environment Yiengprugsawan, Vasoonatara; The Australian National University, National Centre for Epidemiology and Population Health Kjellstrom, Tord; Centre for Global Health Research, Umeå University; The Australian National University, National Centre for Epidemiology and Population Health Seubsman, Sam-ang; Sukhothai Thammathirat Open University, School of Human Ecology Sleigh, Adrian; The Australian National University, National Centre for Epidemiology and Population Health
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Epidemiology, Public health
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, EPIDEMIOLOGY, Epidemiology < TROPICAL MEDICINE
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Heat stress, health, and wellbeing: findings from a large
national cohort of Thai adults
Benjawan Tawatsupa1, 2,*, Vasoontara Yiengprugsawan1, Tord Kjellstrom1, 3,
Sam-ang Seubsman4, Adrian Sleigh1, and the Thai Cohort Study Team
1 National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology
and Environment, the Australian National University, Canberra, Australia
2 Health Impact Assessment Division, Department of Health, Ministry of Public Health,
Nonthaburi, Thailand
3 Centre for Global Health Research, Umeå University, Umeå, Sweden
4 School of Human Ecology, Sukhothai Thammathirat Open University, Nonthaburi, Thailand
*Corresponding author:
Benjawan Tawatsupa,
The Australian National University
Building 62 – NCEPH, Mills Rd, 0200, Canberra, Australia
Email [email protected], [email protected]
Tel: +61 2 6125 5615; Fax: +61 2 6125 0740
The Thai Cohort Study Team
Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn, Suwanee
Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol, Janya
Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai Somboonsook,
Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun, Wanee
Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell, Bruce Caldwell,
Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David Harley, Matthew
Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony McMichael, Tanya
Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara Yiengprugsawan.
Keywords: Heat stress, health, wellbeing, Thailand Word count: 2,294 words
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Abstract
Objectives: This study aims to examine the association between hot season heat stress
interference with daily activities (sleeping, work, travel, housework, exercise) and three graded
holistic health and wellbeing outcomes (energy, emotions, life satisfaction).
Design: A cross-sectional study.
Setting: The setting is tropical and developing countries as Thailand, where high temperature
and high humidity are common, particularly during the hottest seasons.
Participants: This study is based on an ongoing national Thai Cohort Study of distance-
learning open-university adult students (N=60,569) established in 2005 to study the health-risk
transition.
Primary and secondary outcome measures: Health impacts from heat stress in our study are
categorized as physical health impacts (energy levels), mental health impacts (emotions), and
wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds Ratios
(ORs) and 95% confidence intervals using multinomial logistic regression adjusting for a wide
array of potential confounders.
Results: Negative health and wellbeing outcomes (low energy level, emotional problems, and
low life satisfaction) increased with increasing frequency of heat stress interfering with daily
activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and in general
worse than energy level (between 1·31 and 2·91), and life satisfaction (between 1·10 and 2·49).
The worst health outcomes were when heat interfered with sleeping, followed by interference
with daily travel, work, housework and exercise.
Conclusions: In tropical Thailand there already are substantial heat stress impacts on health and
wellbeing. Increasing temperatures from climate change as well as the growing urban population
could significantly worsen the situation. There is a need to improve public health surveillance
and public awareness regarding the risks of heat stress in daily life.
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Article summary
• Article focus:
o To examine the association between heat stress interference with daily activities
(sleeping, work, travel, housework, exercise) during hot season and three graded
holistic health outcomes (energy, emotions, life satisfaction) in Thailand.
• Key messages:
o Negative health and wellbeing outcomes (low energy level, emotional problems,
and low life satisfaction) increased with increasing frequency of heat stress
interfering with daily activities.
o The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
o The results from this study point to the need for improving public health
surveillance and public awareness regarding the risks of heat stress in daily life in
a tropical country like Thailand.
• Strengths and limitations of this study:
o The possible limitation of self-reports, but note that questions on heat stress and
health outcomes were in different parts of the questionnaire.
o The strength of this study is its large scale with participation from a national
group of adults embedded in the socioeconomic mainstream of Thai society and
used the comprehensive questionnaire which captures a detailed assessment of
health and an array of geodemographic, environmental and social attributes.
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Introduction
Over the last decade interest has grown in the impact of global warming on human health.1
Increasing heat stress has substantial adverse effects on population mortality and morbidity.2-5
This information is from developed and temperate countries3 and leaves unanswered questions
for tropical and developing countries where high temperature and humidity are common.
Furthermore, heat stress in tropical cities is increasing due to urban heat island effects caused by
industrial development and urbanisation in developing countries.6
Heat stress can have a major influence on daily human activities. The body absorbs external heat
due to high air temperature and humidity, low air movement, and high solar radiation; as well,
some physical activities generate heat internally.7 Excess heat exposure during normal daily
activities creates a high risk of recurrent dehydration and can cause other effects on physical
health (eg, exhaustion, heat cramps, heat stroke, or death).7 Heat stress affects mood, increases
psychological distress and mental health problems,8-10 and also reduces key human psychological
performance variables.11
Other heat stress impacts may arise from increased mistakes in daily activities and accidental
injuries. As well, disturbed sleep and degraded physical performance from heat exhaustion
reduce work capacity and lead to loss of income.8,12,13 Populations at risk of heat stress are not
only the elderly but also young people and adults who are more likely to carry out heavy labour
outdoors or work indoors without air conditioning or other effective cooling systems during the
hot season.8, 12, 14
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Global warming (or “global heating” may be a better description in relation to Thailand) is now
causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the monthly
mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean minimum
temperature increased even more at 1·44 ˚C.15 Heat stress is already a concern in Thailand and
the observed trends indicate further increase in air temperature.16 A recent study of occupational
heat stress in Thailand by Langkulsen et al17 revealed a very serious problem (“extreme caution”
or “danger”) in an array of work settings (they tested a pottery factory, a power plant, a knife
manufacture site, a construction site and an agricultural site).
Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities18,
19 and for workers.10, 20 However, there is no available information on how much heat interferes
with normal daily activities and heat stress effects on health and well-being in the general Thai
population. Here we report an investigation of heat stress effects on daily activities and on health
and wellbeing in a large national cohort of young and middle aged Thai adults.
Methods
Study population
In 2005, a baseline questionnaire was mailed out to adult students enrolled at Sukhothai
Thammathirat Open University (STOU). The questionnaire was developed by a multi-
disciplinary team in both Thailand and Australia to cover a wide range of topics for a
longitudinal study of the Thai Health-Risk Transition – transformation of the health-risk and
outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge. Overall,
87,134 distance learning students aged 15 to 87 years responded from all areas of Thailand.
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Cohort participants were generally similar to the population of Thailand, especially in the 30-39
years age group, for sex ratio, income and geographical location.21
Data collected included demographic, socioeconomic and geographic characteristics, physical
and mental health status, personal wellbeing, health service use, risk behaviors, injuries, diet,
physical activity, and family background. A four-year follow-up was conducted in 2009 and the
next one is due in 2013.
This report is based on the 2009 follow-up which included questions on heat interference with
normal daily activities. The heat stress and health outcome measures (both described below)
were in different parts of the questionnaire. They could not easily be linked in the respondents
mind so answers on these issues were independent. Covariates analyzed are described with the
results and include age, sex, marital status, geographic location, work status, smoking, drinking,
and Body Mass Index.
Measures of heat stress
Questions related to heat stress were as follows: “How often did the hot period this year interfere
with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work; and 5)
exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times per month’,
‘1-6 times per week’, and ‘every day’. For analysis, we grouped heat stress into ‘never’,
‘sometimes’ (1-3 times per month), and ‘often’ (1-6 times per week or every day).
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Measures of health and wellbeing outcomes
Health is defined by World Health Organization (WHO) as “a complete state of physical, mental,
and social wellbeing and not merely the absence of disease or infirmity”.22 Health impacts from
heat stress in our study are categorized as physical health impacts (eg, energy levels), mental
health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three outcomes were
selected because they match the holistic WHO health definition and represent fundamental health
states. Many other more specific diseases would be expected to follow adverse outcomes for
these health measures (see Discussion).
To measure the physical and mental health impacts we used two questions from the standard
Medical Outcomes Short Form Instrument (SF8) as follows: Energy: “During the past four
weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’, ‘a
little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the past
four weeks, how much have you been bothered by emotional problems (such as feeling anxious,
depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite a lot’, and
‘extremely’. For analysis the last two categories were combined. To measure Wellbeing we used
a standardised question:23, 24 “Thinking about your own life and personal circumstances, how
satisfied are you with your life as a whole?” Scores range from 0 (‘completely dissatisfied’) to 10
(‘completely satisfied’).
Data processing and statistical analysis
Data scanning and editing involved checking the actual questionnaire response against its digital
value using Thai Scandevet, SQL and SPSS software. For analysis we used multinomial logistic
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regression reporting odds ratios (adjusted for potential confounders) based on Stata version 12.25
For all three fundamental health outcomes (energy, emotions, wellbeing), the multinomial
regression estimates the odds with which each of three increasingly severe abnormalities occurs
relative to the odds of an optimal outcome. Individuals with missing data were excluded so totals
presented vary a little according to information available.
Ethical considerations
Ethics approval was obtained from Sukhothai Thammathirat Open University Research and
Development Institute (protocol 0522/10) and the Australian National University Human
Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from all
participants.
Results
Socio-demographic and health characteristics of the 60,569 cohort members followed up in 2009
are presented in Table 1. There were slightly more females (54·8%), 70% were aged less than 40
years, and 55·3% were married. Nearly 20% reported household monthly income of less than
10,000 Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban
areas. Health risk behaviors - regular smoking or regular alcohol drinking -were reported by
7·7% and 13·7%, respectively. By Asian standards,26 half the cohort members were in the normal
weight range, 9·5% were underweight, 18·8% were overweight, and 22·1% were obese.
Daily activities and heat interference frequency categories are shown in Table 2. Heat
interference ‘often’ was reported (in order of frequency) by 37·5% for daily travel, 34·5% for
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work, 29·9% for housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing
frequency outcomes are reported in Table 3: 37·6% reported being very satisfied with their life,
around 40% reported having quite a lot or very much energy in the past 4 weeks and close to
60% reported having slight or no emotional problems in the past 4 weeks.
Daily activities show a clear trend connecting increasing heat interference with worse health and
wellbeing (Table 4). For example, cohort members who experienced heat interference ‘often’
while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently than ‘no’
emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was found for
those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the same trend
was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have also shown
strong gradients connecting frequent heat interference and worse health outcomes.
The multinomial logistic regression, adjusting for a wide array of potential confounders (see
footnote for Table 5), supported the descriptive results. For all three health outcomes, when each
of the three graded adverse outcome categories is compared to the optimal outcome, the relative
odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for each health
outcome, more heat interference associates more strongly with a given grade of abnormality).
And 95% confidence intervals for all odds ratios indicated statistical significance. So heat stress
interfering with normal daily activities (sleep, housework, travel, work, exercise) associates with
adverse outcomes for all three holistic measures of health. For example, reporting heat
interference ‘often’ while sleeping was strongly associated with ‘little or none’ energy [OR =
2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81, 95% CI 4·32-5·36] and
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‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work, reporting heat interference
‘often’ was associated with ‘little or none’ energy [OR = 2·45, 95% CI 2·22-2·71] and ‘extreme’
emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar results were found during daily
travel and doing housework. A statistically significant association was also found for heat
inference during exercise but the magnitude of the effect was lower than for other activities.
Discussion
Our study shows that climate-related heat stress in tropical Thailand adversely affects self-
reported health and wellbeing if the heat interferes with daily activities such as sleep, housework,
travel, work, and exercise. The large study group included young and middle-age Thai adults,
mostly doing paid work, with over half residing in urban areas. These people are active and over
20% reported often experiencing heat interference for daily activities during the hot season.
Daily travel and work were sources of heat stress more often than other activities, probably
because they involve time spent in traffic or outdoors during hot periods. Other activities such as
housework have less heat stress than daily travel and work, perhaps because these activities are
home-based where air-conditioning or other ventilation is available.
We found negative health and wellbeing outcomes (low life satisfaction, low energy level, and
emotional problems) increased with higher frequency of heat stress while performing daily
activities. Odds Ratios of heat stress across all daily activities for emotional problems are
between 1·55 and 4·81 and in general worse than energy level effects (between 1·31 and 2·91)
and life satisfaction effects (between 1·10 and 2·49). The worst health outcomes were for heat
stress while sleeping followed by daily travel, work, housework and exercise.
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Our studied outcomes were holistic fundamental measures of health. We can expect that those
who had abnormal findings would also (already or eventually) manifest other more specific
chronic diseases such as depression, obesity, hypertension, and kidney disease. If so, the eventual
burden of heat-related disease will be higher than currently recognized.27-29
We acknowledge the possible limitation of self-reports, but note that questions on heat stress and
health outcomes were in different parts of the questionnaire. However, the findings show a
strong and highly consistent trend especially for adverse health effects of frequent heat
interference during sleep, daily travel, and work. The strength of this study is its large scale with
participation from a national group of adults embedded in the socioeconomic mainstream of Thai
society. Other strengths include the comprehensive questionnaire which captures a detailed
assessment of health and an array of geodemographic, environmental and social attributes. Also,
the cohort has been set up for future longitudinal analysis which will provide better insight into
causal pathways between heat stress and subsequent health outcomes in the long run.
Our findings add to some previous reports on working in hot environments which found that heat
stress significantly reduced people’s motivation to do their work. Lan et al30 assessed office
workers’ perceptions of thermal environment, emotions, well-being, and motivation to work, and
found that participants had lower motivation to work and experienced more negative moods in
hot environments. Anderson found that the prolonged, continuous repetitive actions required to
maintain performance at work and achieve target goals (such as getting a job finished) can lead
to hypertension.31 And when more effort was required to complete a task in hot conditions loss
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of motivation was experienced leading to lower productivity and increased injury risk. The
impact of heat stress on psychological performance variables11 is a likely factor in these work
related impacts of heat. Psychological effects of heat stress have been noted in other settings as
well. Nitschke et al32 reported a positive association between high ambient temperature and
hospital admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses
for which admissions increased included anxiety, symptomatic mood disorders, and
psychological development disorders among elderly people when temperature exceeded
26·7°C.33 Moreover, excessive heat stress exposure may also increase violence.31-34 Increasing
heat stress had been associated with higher rates of aggressive behavior,35 and higher violent
suicide rates.36 In a meta-analysis, Bouchama et al37 concluded that pre-existing mental health
problems tripled the risk of all-cause mortality during a heat wave. A related issue is the physical
and psychological exhaustion caused by extreme heat stress.7
Thai populations are at high risk of heat stress during daily activities. Also, in Thailand an
anticipated increase in temperature from climate change plus the growing urban population could
significantly increase heat impacts on health and wellbeing. There is a need for improvements in
public health surveillance and public awareness regarding the risks of heat stress which hitherto
have been considered unremarkable in such a tropical environment.
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Tables
Table 1 Socio-demographic and health characteristics of Thai cohort members in 2009
Cohort characteristics N = 60,569 %
Demographic characteristics
Sex Male 45.3
Female 54.8
Age (year) ≤ 29 27.4
30-39 42.6
40+ 30.0
Marital status Married 55.3
Never married 37.9
Separated, divorced, widowed 6.8
Socio-geographic characteristics
Monthly income (Baht)* <10,000 18.8
10,000-19,999 22.4
20,000-30,000 35.7
>30,000 23.1
Work status Doing paid work 73.2
Unpaid family workers 7.3
Seeking work 2.2
Others 17.3
Residence Rural residence 44.0
Urban residence 56.0
Health risk behaviors
Regular smokers 7.7
Regular alcohol drinkers 13.7
Body Mass Index (kg/m2)
Underweight (<18.5) 9.5
Normal (18.5-22.9) 49.5
Overweight at risk (23-24.9) 18.8
Obese (25+) 22.1
*Household monthly income in 2009 (US$ = 35 Baht)
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Table 2 Daily activities and heat interference category among Thai cohort members in 2009
Daily activities
N = 60,569
Heat interference (%)
Not applicable* Never Sometimes Often
Sleeping 15.7 24.3 32.5 27.4
Housework 1.3 37.1 31.7 29.9
Daily travel 3.0 33.7 25.8 37.5
Work 14.0 30.3 21.2 34.5
Exercise 0.8 43.1 30.1 25.9
*Use air conditioner
Table 3 Health and wellbeing outcomes among Thai cohort members in 2009
Outcomes
N = 60,569
%
Overall life satisfaction (score ranged from 0 to 10)
9-10 very satisfied (highest) 37.6
8 (high) 28.8
6-7 (medium) 21.7
0-5 not very satisfied (low) 12.0
Energy level in the past 4 weeks
very much 14.4
quite a lot 25.8
some 48.4
a little or none 11.3
Emotional problems in the past 4 weeks
not at all 14.9
slightly 44.0
moderately 32.0
quite a lot/extremely 9.1
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Table 4 Frequency of heat interference with daily activities by health & wellbeing outcomes among cohort members
Daily activities and
heat interference
category
Health and wellbeing outcomes N=60,569
% Life satisfaction
score ranged from 0 to 10
% Energy level
in the past 4 weeks
% Emotional problems
in the past 4 weeks
9-10
highest
8
high
6-7
medium
0-5
low
very much quite a lot some
little/ none not at all slightly
moderate
extreme
Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)
never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6
sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3
often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9
Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)
never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7
sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4
often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9
Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)
never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2
sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4
often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0
Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)
never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6
sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9
often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7
Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)
never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2
sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9
often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2
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Table 5 Association between heat interference with daily activities and health & wellbeing outcomes among cohort members
Heat
interference
category
N=60,569
Adjusted* Odds Ratios and 95% Confidence Interval
Life satisfaction (score 0-10)** Energy level in the past 4 weeks Emotional problems in the past 4 weeks
high
vs
highest
medium
vs
highest
low
vs
highest
quite a lot
vs
very much
some
vs
very much
little/none
vs
very much
slightly
vs
not at all
moderate
vs
not at all
extreme
vs
not at all
Sleep
never ref ref ref ref ref ref ref ref ref
sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]
often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]
Housework
never ref ref ref ref ref ref ref ref ref
sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]
often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]
Daily travel
never ref ref ref ref ref ref ref ref ref
sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]
often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]
Work
never ref ref ref ref ref ref ref ref ref
sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]
often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]
Exercise
never ref ref ref ref ref ref ref ref ref
sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]
often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]
*Multivariate regression adjusting for potential confounders: age, sex, marital status, work status, household income, urban-rural residence, exercise, housework, hours of
sleep, body mass index, smoking , and drinking
**Life satisfaction scores: highest = 9-10, high = 8, medium = 6-7, low = 0-5
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Acknowledgments
This study was supported by the International Collaborative Research Grants Scheme with
joint grants from the Wellcome Trust UK (GR071587MA) and the Australian National Health
and Medical Research Council (NHMRC 268055), and as a global health grant from the
NHMRC (585426). These funding bodies play no role in the preparation or submission of this
manuscript. We thank the staff at Sukhothai Thammathirat Open University (STOU) who
assisted with student contact, and the STOU students who are participating in the cohort
study. We also thank Dr Bandit Thinkamrop and his team from Khon Kaen University for
guiding us successfully through the complex data processing.
Competing interests
We declare that we have non-financial competing interests.
Contributor statement
The corresponding author had full access to all data used in the study and had final
responsibility for the decision to submit for publication. BT and VY conceptualized the
analysis for this paper with contributions from all authors. BT and VY wrote the first draft.
BT did the literature search and VY did statistical analyses. TK had the initial idea for the
heat stress study. SS and AS conceived and executed the Thai Cohort Study and assisted with
the writing and interpretation. All authors contributed to and approved the final version.
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Reference lists
1. Confalonieri U, Menne B, Akhtar R, et al. Human Health. Cambridge, UK: Cambridge
University Press; 2007; http://www.ipcc-wg2.org (accessed 13 March 2012).
2. Basu R, Samet JM. Relation between elevated ambient temperature and mortality: A
review of the epidemiologic evidence. Epidemiol Rev 2002;24(2):190-202.
3. Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health
2008;29:41-55.
4. Basu R. High ambient temperature and mortality: A review of epidemiologic studies from
2001 to 2008. Environ Health 2009;8(40).
5. Bi P, Williams S, Loughnan M, et al. The effects of extreme heat on human mortality and
morbidity in Australia: Implications for public health. Asia Pac J Public Health 2011;23(2
Suppl):27S-36S.
6. Campbell-Lendrum D, Corvalan C. Climate change and developing-country cities:
implications for environmental health and equity. J Urban Health 2007;84(1 Suppl):i109-17.
7. Parsons K. Human thermal environments: the effects of hot, moderate, and cold
environments on human health, comfort and performance. 2nd ed. London: Taylor & Francis;
2003.
8. Kjellstrom T. Climate change, direct heat exposure, health and well-being in low and
middle-income countries. Glob Health Action 2009;2:1-3.
9. Berry HL, Bowen K, Kjellstrom T. Climate change and mental health: a causal pathways
framework. Int J Public Health 2010;55(2):123-32.
Page 18 of 25
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on July 18, 2020 by guest. Protected by copyright.
http://bmjopen.bm
j.com/
BM
J Open: first published as 10.1136/bm
jopen-2012-001396 on 6 Novem
ber 2012. Dow
nloaded from
For peer review only
Tawatsupa Page 19
10. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. The association between overall health,
psychological distress, and occupational heat stress among a large national cohort of 40,913
Thai workers. Glob Health Action 2010;3(5034).
11. Hancock PA, Ross JM, Szalma JL. A meta-analysis of performance response under thermal
stressors. Hum Factors 2007;49(5):851-77.
12. Kjellstrom T. Climate change exposures, chronic disease and mental health in urban
populations:a threat to health security, particularly for the poor and disadvantaged. Kobe,
Japan: World Health Organization Centre for Health and Development; 2009;
http://www.who.int/kobe_centre/publications/cc_work_ability.pdf (accessed 7 March 2012).
13. Kjellstrom T, Holmer I, Lemke B. Workplace heat stress, health and productivity - an
increasing challenge for low and middle-income countries during climate change. Glob Health
Action 2009;2.
14. Kjellstrom T, Gabrysch S, Lemke B, et al. The "Hothaps" program for assessing climate
change impacts on occupational health and productivity: an invitation to carry out field studies
Glob Health Action 2009;2.
15. Limsakul A, Goes JI. Empirical evidence for interannual and longer period variability in
Thailand surface air temperatures. Atmos Res 2008;87(2):89-102.
16. Thai Meteorological Department. Climate change in Thailand for last 52 years. Bangkok:
Meteorological Department, Thailand; 2007; http://www.tmd.go.th/info/info.php?FileID=86
(accessed 4 February 2012).
17. Langkulsen U, Vichit-Vadakan N, Taptagaporn S. Health impact of climate change on
occupational health and productivity in Thailand. Glob Health Action 2010;3(5607).
Page 19 of 25
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
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j.com/
BM
J Open: first published as 10.1136/bm
jopen-2012-001396 on 6 Novem
ber 2012. Dow
nloaded from
For peer review only
Tawatsupa Page 20
18. McMichael AJ, Wilkinson P, Kovats RS, et al. International study of temperature, heat and
urban mortality: the 'ISOTHURM' project. Int J Epidemiol 2008;37(5):1121-31.
19. Pudpong N, Hajat S. High temperature effects on out-patient visits and hospital
admissions in Chiang Mai, Thailand. Sci Total Environ 2011;409:5260–67.
20. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. Association between occupational heat stress
and kidney disease among 37,816 workers in the Thai Cohort Study (TCS). J Epidemiol 2012;22.
21. Sleigh A, Seubsman S, Bain C. Cohort profile: The Thai Cohort of 87,134 Open University
students. Int J Epidemiol 2008;37(2):266-72.
22. Grad FP. The Preamble of the Constitution of the World Health Organization. Bull World
Health Organ 2002;80(12):981-84.
23. Cummins RA, Eckersley R, Pallant J, et al. Developing a National Index of Subjective
Wellbeing: The Australian Unity Wellbeing Index. Soc Indic Res 2003;64(2):159-90.
24. Yiengprugsawan V, Seubsman S, Khamman S, et al. Personal wellbeing index in a national
cohort of 87,134 Thai adults. Soc Indic Res 2010;98(2):201-15.
25. StataCorp. Stata 12.0 for Windows. College Station TX: StataCorporation; 2011.
26. Kanazawa M, Yoshiike N, Osaka T, et al. Criteria and classification of obesity in Japan and
Asia-Oceania Asia Pac J Clin Nutr 2002;11:S732-7.
27. McMichael AJ, Woodruff RE, Hales S. Climate change and human health: present and
future risks. Lancet 2006;367(9513):859-69.
28. Hajat S, O'Connor M, Kosatsky T. Health effects of hot weather: from awareness of risk
factors to effective health protection. Lancet 2010;375(9717):856-63.
Page 20 of 25
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
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J Open: first published as 10.1136/bm
jopen-2012-001396 on 6 Novem
ber 2012. Dow
nloaded from
For peer review only
Tawatsupa Page 21
29. Kjellstrom T, Butler AJ, Lucas RM, et al. Public health impact of global heating due to
climate change: potential effects on chronic non-communicable diseases. Int J Public Health
2010;55:97-103.
30. Lan L, Lian Z, Pan L. The effects of air temperature on office workers’ well-being,
workload and productivity-evaluated with subjective ratings. Appl Ergon 2010;42(1):29-36.
31. Anderson C. Heat and violence. Curr Dir Psychol Sci 2001;10(1):33-8.
32. Nitschke M, Tucker GR, Bi P. Morbidity and mortality during heatwaves in metropolitan
Adelaide. Med J Aust 2007;187(11):662-5.
33. Hansen AL, Bi P, Nitschke M, et al. The effect of heat waves on mental health in a
temperate Australian city. Environ Health Perspect 2008;116(10):1369-75.
34. Anderson C, Anderson K, Dorr N, et al. Temperature and aggression Adv Experimental
Social Psychology 2000;32:63-133.
35. Cheatwood D. The effects of weather on homicide. J Quant Criminol 1995;11(1):51-70.
36. Maes M, De Meyer F, Thompson P, et al. Synchronized annual rhythms in violent suicide
rate, ambient temperature and the light-dark span. Acta Psychiatr Scand 1994;90(5):391-6.
37. Bouchama A, Dehbi M, Mohamed G, et al. Prognostic factors in heat wave-related deaths:
A meta-analysis. Arch Intern Med 2007;167(20):2170-6.
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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cross-sectional studies
Section/Topic Item
# Recommendation Reported on page #
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 2
(b) Provide in the abstract an informative and balanced summary of what was done and
what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 4
Objectives 3 State specific objectives, including any prespecified hypotheses 5
Methods
Study design 4 Present key elements of study design early in the paper 7
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
5
Participants
6
(a) Give the eligibility criteria, and the sources and methods of selection of participants 5
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
6
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of assessment
(measurement). Describe comparability of assessment methods if there is more than
one group
6
(Our heat exposed group include respondents who
reported heat interfere their daily activities at 1-6 times
per week or every day. An unexposed group include
those who reported never experienced heat or 1-3 times
per month)
Bias 9 Describe any efforts to address potential sources of bias 6
Study size 10 Explain how the study size was arrived at 8
Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe
which groupings were chosen and why
7
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 7
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(b) Describe any methods used to examine subgroups and interactions 7
(c) Explain how missing data were addressed 8
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study, completing
follow-up, and analysed
8
(b) Give reasons for non-participation at each stage -
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
8
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures 9
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders were
adjusted for and why they were included
9
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity
analyses
10
Discussion
Key results 18 Summarise key results with reference to study objectives 10
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
11
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
11
Generalisability 21 Discuss the generalisability (external validity) of the study results 11
Other information
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Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
17
*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
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Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults
Journal: BMJ Open
Manuscript ID: bmjopen-2012-001396.R1
Article Type: Research
Date Submitted by the Author: 20-Jul-2012
Complete List of Authors: Tawatsupa, Benjawan; Health Impact Assessment Division, Department of Health; National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology and Environment Yiengprugsawan, Vasoonatara; The Australian National University, National Centre for Epidemiology and Population Health Kjellstrom, Tord; Centre for Global Health Research, Umeå University; The Australian National University, National Centre for Epidemiology and Population Health Seubsman, Sam-ang; Sukhothai Thammathirat Open University, School of Human Ecology Sleigh, Adrian; The Australian National University, National Centre for Epidemiology and Population Health
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Epidemiology, Public health
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, EPIDEMIOLOGY, Epidemiology < TROPICAL MEDICINE
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ovember 2012. D
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Heat stress, health, and wellbeing: findings from a large
national cohort of Thai adults
Benjawan Tawatsupa1, 2,*, Vasoontara Yiengprugsawan1, Tord Kjellstrom1, 3,
Sam-ang Seubsman4, Adrian Sleigh1, and the Thai Cohort Study Team
1 National Centre for Epidemiology and Population Health, ANU College of Medicine,
Biology and Environment, the Australian National University, Canberra, Australia
2 Health Impact Assessment Division, Department of Health, Ministry of Public Health,
Nonthaburi, Thailand
3 Centre for Global Health Research, Umeå University, Umeå, Sweden
4 School of Human Ecology, Sukhothai Thammathirat Open University, Nonthaburi, Thailand
*Corresponding author:
Benjawan Tawatsupa,
The Australian National University
Building 62 – NCEPH, Mills Rd, 0200, Canberra, Australia
Email [email protected], [email protected]
Tel: +61 2 6125 5615; Fax: +61 2 6125 0740
The Thai Cohort Study Team
Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn,
Suwanee Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol,
Janya Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai
Somboonsook, Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun,
Wanee Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell,
Bruce Caldwell, Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David
Harley, Matthew Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony
McMichael, Tanya Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara
Yiengprugsawan.
Keywords: Heat stress, health, wellbeing, Thailand Word count: 2,607 words
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Abstract
Objectives: This study aims to examine the association between self-reported heat stress
interference with daily activities (sleeping, work, travel, housework, exercise) and three
graded holistic health and wellbeing outcomes (energy, emotions, life satisfaction).
Design: A cross-sectional study.
Setting: The setting is tropical and developing countries as Thailand, where high temperature
and high humidity are common, particularly during the hottest seasons.
Participants: This study is based on an ongoing national Thai Cohort Study of distance-
learning open-university adult students (N=60,569) established in 2005 to study the health-
risk transition.
Primary and secondary outcome measures: Health impacts from heat stress in our study
are categorized as physical health impacts (energy levels), mental health impacts (emotions),
and wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds
Ratios (ORs) and 95% confidence intervals using multinomial logistic regression adjusting
for a wide array of potential confounders.
Results: Negative health and wellbeing outcomes (low energy level, emotional problems,
and low life satisfaction) increased with increasing frequency of heat stress interfering with
daily activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and
in general worse than energy level (between 1·31 and 2·91), and life satisfaction (between
1·10 and 2·49). The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
Conclusions: In tropical Thailand there already are substantial heat stress impacts on health
and wellbeing. Increasing temperatures from climate change plus the ageing and urbanisation
of the population could significantly worsen the situation. There is a need to improve public
health surveillance and public awareness regarding the risks of heat stress in daily life.
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Article summary
• Article focus:
o To examine the association between self-reported heat stress interference with
daily activities (sleeping, work, travel, housework, exercise) during hot season
and three graded holistic health outcomes (energy, emotions, life satisfaction)
in Thailand.
• Key messages:
o Negative health and wellbeing outcomes (low energy level, emotional
problems, and low life satisfaction) increased with increasing frequency of heat
stress interfering with daily activities.
o The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
o The results from this study point to the need for improving public health
surveillance and public awareness regarding the risks of heat stress in daily life
in a tropical country like Thailand.
• Strengths and limitations of this study:
o The possible limitation of self-reports, but note that questions on heat stress
and health outcomes were in different parts of the questionnaire.
o The strength of this study is its large scale with participation from a national
group of adults embedded in the socioeconomic mainstream of Thai society
and used the comprehensive questionnaire which captures a detailed
assessment of health and an array of geodemographic, environmental and
social attributes.
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Introduction
Over the last decade interest has grown in the impact of global warming on human health.(1)
Increasing heat stress has substantial adverse effects on population mortality and
morbidity.(2-5) This information is from developed and temperate countries(3) and leaves
unanswered questions for tropical and developing countries where high temperature and
humidity are common. Furthermore, heat stress in tropical cities is increasing due to urban
heat island effects caused by industrial development and urbanisation in developing
countries.(6)
Heat stress can have a major influence on daily human activities. The body absorbs external
heat due to high air temperature and humidity, low air movement, and high solar radiation; as
well, some physical activities generate heat internally.(7) Excess heat exposure during normal
daily activities creates a high risk of recurrent dehydration and can cause other effects on
physical health (eg, exhaustion, heat cramps, heat stroke, or death).(7) Heat stress affects
mood, increases psychological distress and mental health problems,(8-10) and also reduces
key human psychological performance variables.(11)
Other heat stress impacts may arise from increased mistakes in daily activities and accidental
injuries. As well, disturbed sleep and degraded physical performance from heat exhaustion
reduce work capacity and lead to loss of income.(8, 12-13) Populations at risk of heat stress
are not only the elderly but also young people and adults who are more likely to carry out
heavy labour outdoors or work indoors without air conditioning or other effective cooling
systems during the hot season.(8, 12, 14)
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In tropical Thailand, hot and humid conditions are common, especially in the hot season
(March - June). The monthly maximum, mean and minimum temperatures averaged from
1999 to 2008 were around 33°C, 27°C, and 22°C respectively with the averaged relative
humidity at 75%. The monthly maximum temperatures averaged during ten years varied little
by region (32-33°C) and were highest in the North region during April (40°C) and lowest in
the same region during December (24°C).(Tawatsupa et al, unpublished data, 2012)
Global warming (or “global heating” may be a better description in relation to Thailand) is
now causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the
monthly mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean
minimum temperature increased even more at 1·44 ˚C.(15) Heat stress is already a concern in
Thailand and the observed trends indicate further increase in air temperature.(16) A recent
study of occupational heat stress in Thailand by Langkulsen et al(17) revealed a very serious
problem (“extreme caution” or “danger”) in an array of work settings (they tested a pottery
factory, a power plant, a knife manufacture site, a construction site and an agricultural site).
Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities
(18-19) and for workers.(10, 20) However, there is no available information on how much
heat interferes with normal daily activities and heat stress effects on health and well-being in
the general Thai population. Here we report an investigation of heat stress effects on daily
activities and on health and wellbeing in a large national cohort of young and middle aged
Thai adults.
Methods
Study population
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In 2005, a baseline questionnaire was mailed out to adult students enrolled at Sukhothai
Thammathirat Open University (STOU). The questionnaire was developed by a multi-
disciplinary team in both Thailand and Australia to cover a wide range of topics for a
longitudinal study of the Thai Health-Risk Transition – transformation of the health-risk and
outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge.
Overall, 87,134 distance learning students aged 15 to 87 years responded from all areas of
Thailand. Cohort participants were generally similar to the population of Thailand, especially
in the 30-39 years age group, for sex ratio, income and geographical location.(21)
Data collected included demographic, socioeconomic and geographic characteristics, physical
and mental health status, personal wellbeing, health service use, risk behaviors, injuries, diet,
physical activity, and family background. A four-year follow-up was conducted in 2009 and
the next one is due in 2013.
This report is based on the 2009 follow-up which included questions on heat interference with
normal daily activities. The heat stress and health outcome measures (both described below)
were in different parts of the questionnaire. They could not easily be linked in the respondents
mind so answers on these issues were independent. Covariates analyzed are described with
the results and include age, sex, marital status, geographic location, work status, smoking,
drinking, and Body Mass Index.
Measures of heat stress
Questions related to heat stress were as follows: “How often did the hot period this year
interfere with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work;
and 5) exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times
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per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means heat
stress causing an uncomfortable feeling when doing those daily activities. For analysis, we
grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per month), and ‘often’
(1-6 times per week or every day).
Measures of health and wellbeing outcomes
Health is defined by World Health Organization (WHO) as “a complete state of physical,
mental, and social wellbeing and not merely the absence of disease or infirmity”.(22) Health
impacts from heat stress in our study are categorized as physical health impacts (eg, energy
levels), mental health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three
outcomes were selected because they match the holistic WHO health definition and represent
fundamental health states. Many other more specific diseases would be expected to follow
adverse outcomes for these health measures (see Discussion).
To measure the physical and mental health impacts we used two questions from the standard
Medical Outcomes Short Form Instrument (SF8) as follows: Energy: “During the past four
weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’,
‘a little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the
past four weeks, how much have you been bothered by emotional problems (such as feeling
anxious, depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite
a lot’, and ‘extremely’. For analysis the last two categories were combined. To measure
Wellbeing we used a standardised question:(23-24) “Thinking about your own life and
personal circumstances, how satisfied are you with your life as a whole?” Scores range from 0
(‘completely dissatisfied’) to 10 (‘completely satisfied’).
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Data processing and statistical analysis
Data scanning and editing involved checking the actual questionnaire response against its
digital value using Thai Scandevet, SQL and SPSS software. For analysis we used
multinomial logistic regression reporting odds ratios (adjusted for potential confounders)
based on Stata version 12.(25) For all three fundamental health outcomes (energy, emotions,
wellbeing), the multinomial regression estimates the odds with which each of three
increasingly severe abnormalities occurs relative to the odds of an optimal outcome.
Individuals with missing data were excluded so totals presented vary a little according to
information available.
Ethical considerations
Ethics approval was obtained from Sukhothai Thammathirat Open University Research and
Development Institute (protocol 0522/10) and the Australian National University Human
Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from
all participants.
Results
We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not shown).
The two groups were similar for age, sex ratio, employment, income, and health outcomes
studied here (energy levels, emotional problems, life satisfaction). Socio-demographic and
health characteristics of the 60,569 cohort members followed up in 2009 are presented in
Table 1. There were slightly more females (54·8%), 70% were aged less than 40 years, and
55·3% were married. Nearly 20% reported household monthly income of less than 10,000
Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban areas.
Health risk behaviors - regular smoking or regular alcohol drinking -were reported by 7·7%
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and 13·7%, respectively. By Asian standards,(26) half the cohort members were in the normal
weight range, 9·5% were underweight, 18·8% were overweight, and 22·1% were obese.
We noted that prevalence of ‘often’ heat interference for each daily activity are not much
different in different regions of Thailand (33-42% for daily travel, 29-38% for work, 26-32%
for housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat
interference frequency categories are summarized in Table 2. Heat interference ‘often’ was
reported (in order of frequency) by 37·5% for daily travel, 34·5% for work, 29·9% for
housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing frequency
outcomes are reported in Table 3: 37·6% reported being very satisfied with their life, around
15% reported having very much energy in the past 4 weeks and close to 11% reported no
emotional problems in the past 4 weeks.
Daily activities show a clear trend connecting increasing heat interference with worse health
and wellbeing (Table 4). For example, cohort members who experienced heat interference
‘often’ while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently
than ‘no’ emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was
found for those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the
same trend was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have
also shown strong gradients connecting frequent heat interference and worse health outcomes.
The multinomial logistic regression, adjusting for a wide array of potential confounders (see
footnote for Table 5), supported the descriptive results. For all three health outcomes, when
each of the three graded adverse outcome categories is compared to the optimal outcome, the
relative odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for
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each health outcome, more heat interference associates more strongly with a given grade of
abnormality). And 95% confidence intervals for all odds ratios indicated statistical
significance. So heat stress interfering with normal daily activities (sleep, housework, travel,
work, exercise) associates with adverse outcomes for all three holistic measures of health. For
example, reporting heat interference ‘often’ while sleeping was strongly associated with ‘little
or none’ energy [OR = 2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81,
95% CI 4·32-5·36] and ‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work,
reporting heat interference ‘often’ was associated with ‘little or none’ energy [OR = 2·45,
95% CI 2·22-2·71] and ‘extreme’ emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar
results were found during daily travel and doing housework. A statistically significant
association was also found for heat inference during exercise but the magnitude of the effect
was lower than for other activities.
Discussion
Our study shows that climate-related heat stress in tropical Thailand adversely affects self-
reported health and wellbeing if the heat interferes with daily activities such as sleep,
housework, travel, work, and exercise. The large study group included young and middle-age
Thai adults, mostly doing paid work, with over half residing in urban areas. These people are
active and over 20% reported often experiencing heat interference for daily activities during
the hot season. Daily travel and work were sources of heat stress more often than other
activities, probably because they involve time spent in traffic or outdoors during hot periods.
Other activities such as housework have less heat stress than daily travel and work, perhaps
because these activities are home-based where air-conditioning or other ventilation is
available.
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We found negative health and wellbeing outcomes (low life satisfaction, low energy level,
and emotional problems) increased with higher frequency of heat stress while performing
daily activities. Odds Ratios of heat stress across all daily activities for emotional
problems are between 1·55 and 4·81 and in general worse than energy level effects (between
1·31 and 2·91) and life satisfaction effects (between 1·10 and 2·49). The worst health
outcomes were for heat stress while sleeping followed by daily travel, work, housework and
exercise.
Elsewhere we have completed detailed analyses of associations between heat stress and self-
reported health outcomes in the cohort using the questions from SF8 (10). Our studied
outcomes in this report were holistic fundamental measures of health. We can expect that
those who had abnormal findings would also (already or eventually) manifest other more
specific chronic diseases such as depression, obesity, hypertension, and kidney disease. If so,
the eventual burden of heat-related disease will be higher than currently recognized.(27-29)
We acknowledge the possible limitation of self-reports, but note that questions on heat stress
and health outcomes were in different parts of the questionnaire. However, the findings show
a strong and highly consistent trend especially for adverse health effects of frequent heat
interference during sleep, daily travel, and work. The strength of this study is its large scale
with participation from a national group of adults embedded in the socioeconomic mainstream
of Thai society. Other strengths include the comprehensive questionnaire which captures a
detailed assessment of health and an array of geodemographic, environmental and social
attributes. Also, the cohort has been set up for future longitudinal analysis which will provide
better insight into causal pathways between heat stress and subsequent health outcomes in the
long run.
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Our findings add to some previous reports on working in hot environments which found that
heat stress significantly reduced people’s motivation to do their work. Lan et al (30) assessed
office workers’ perceptions of thermal environment, emotions, well-being, and motivation to
work, and found that participants had lower motivation to work and experienced more
negative moods in hot environments. Anderson found that the prolonged, continuous
repetitive actions required to maintain performance at work and achieve target goals (such as
getting a job finished) can lead to hypertension.(31) And when more effort was required to
complete a task in hot conditions loss of motivation was experienced leading to lower
productivity and increased injury risk. The impact of heat stress on psychological
performance variables (11) is a likely factor in these work related impacts of heat.
Psychological effects of heat stress have been noted in other settings as well. Nitschke et al
(32) reported a positive association between high ambient temperature and hospital
admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses for
which admissions increased included anxiety, symptomatic mood disorders, and
psychological development disorders among elderly people when temperature exceeded
26·7°C.(33) Moreover, excessive heat stress exposure may also increase violence.(31-34)
Increasing heat stress had been associated with higher rates of aggressive behavior,(35) and
higher violent suicide rates.(36) In a meta-analysis, Bouchama et al (37) concluded that pre-
existing mental health problems tripled the risk of all-cause mortality during a heat wave. A
related issue is the physical and psychological exhaustion caused by extreme heat stress. (7)
In our study, we found that heat stress in Thailand is not only a problem at work but also heat
stress interferes with other daily activities including sleeping, daily travel, housework and
exercise. The results of our study complement other Thai research about adverse effects of
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heat. One recent report shows that heat stress in Thailand is a very serious problem in a wide
variety of work settings (17). McMichael et al (18) and Guo et al (38) found a temperature–
mortality association and Pudpong et al (19) found heat related excess hospital admissions.
Worker studies in Thailand related occupational heat stress, kidney disease and psychological
distress.(10, 20)
We conclude that Thai populations are at high risk of heat stress during daily activities. Also,
in Thailand an anticipated increase in temperature from climate change plus the ageing and
urbanisation of the population could significantly increase heat impacts on health and
wellbeing. There is a need for improvements in public health surveillance and public
awareness regarding the risks of heat stress which hitherto have been considered
unremarkable in such a tropical environment.
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Tables
Table 1 Socio-demographic and health characteristics of Thai cohort members in 2009
Cohort characteristics N = 60,569 %
Demographic characteristics
Sex Male 45.3
Female 54.8
Age (year) ≤ 29 27.4
30-39 42.6
40+ 30.0
Marital status Married 55.3
Never married 37.9
Separated, divorced, widowed 6.8
Socio-geographic characteristics
Monthly income (Baht)* ≤10,000 18.8
10,001-20,000 22.4
20,001-30,000 35.7
>30,000 23.1
Work status Doing paid work 73.2
Unpaid family workers 7.3
Seeking work 2.2
Others 17.3
Residence Rural residence 44.0
Urban residence 56.0
Health risk behaviors
Regular smokers 7.7
Regular alcohol drinkers 13.7
Body Mass Index (kg/m2)
Underweight (<18.5) 9.5
Normal (18.5-22.9) 49.5
Overweight at risk (23-24.9) 18.8
Obese (25+) 22.1
*Household monthly income in 2009 (US$ = 35 Baht)
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Table 2 Daily activities and heat interference category among Thai cohort members in 2009
Daily activities
N = 60,569
Heat interference (%)
Not applicable* Never Sometimes Often
Sleeping 15.7 24.3 32.5 27.4
Housework 1.3 37.1 31.7 29.9
Daily travel 3.0 33.7 25.8 37.5
Work 14.0 30.3 21.2 34.5
Exercise 0.8 43.1 30.1 25.9
*Use air conditioner
Table 3 Health and wellbeing outcomes among Thai cohort members in 2009
Outcomes
N = 60,569
%
Overall life satisfaction (score ranged from 0 to 10)
9-10 very satisfied (highest) 37.6
8 (high) 28.8
6-7 (medium) 21.7
0-5 not very satisfied (low) 12.0
Energy level in the past 4 weeks
very much 14.9
quite a lot 44.0
some 32.0
a little or none 9.1
Emotional problems in the past 4 weeks
not at all 11.3
slightly 48.4
moderately 25.8
quite a lot/extremely 14.5
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Table 4 Frequency of heat interference with daily activities by health & wellbeing outcomes among cohort members
Daily activities and
heat interference
category
Health and wellbeing outcomes N=60,569
% Life satisfaction
score ranged from 0 to 10
% Energy level
in the past 4 weeks
% Emotional problems
in the past 4 weeks
9-10
highest
8
high
6-7
medium
0-5
low
very much quite a lot some
little/ none not at all slightly
moderate
extreme
Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)
never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6
sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3
often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9
Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)
never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7
sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4
often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9
Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)
never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2
sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4
often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0
Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)
never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6
sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9
often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7
Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)
never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2
sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9
often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2
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Table 5 Association between heat interference with daily activities and health & wellbeing outcomes among cohort members
Heat
interference
category
N=60,569
Adjusted* Odds Ratios and 95% Confidence Interval
Life satisfaction (score 0-10)** Energy level in the past 4 weeks Emotional problems in the past 4 weeks
high
vs
highest
medium
vs
highest
low
vs
highest
quite a lot
vs
very much
some
vs
very much
little/none
vs
very much
slightly
vs
not at all
moderate
vs
not at all
extreme
vs
not at all
Sleep
never ref ref ref ref ref ref ref ref ref
sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]
often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]
Housework
never ref ref ref ref ref ref ref ref ref
sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]
often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]
Daily travel
never ref ref ref ref ref ref ref ref ref
sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]
often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]
Work
never ref ref ref ref ref ref ref ref ref
sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]
often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]
Exercise
never ref ref ref ref ref ref ref ref ref
sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]
often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]
*Multivariate regression adjusting for potential confounders: age, sex, marital status, work status, household income, urban-rural residence, exercise, housework, hours of
sleep, body mass index, smoking , and drinking
**Life satisfaction scores: highest = 9-10, high = 8, medium = 6-7, low = 0-5
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Acknowledgments
This study was supported by the International Collaborative Research Grants Scheme with
joint grants from the Wellcome Trust UK (GR071587MA) and the Australian National Health
and Medical Research Council (NHMRC 268055), and as a global health grant from the
NHMRC (585426). These funding bodies play no role in the preparation or submission of this
manuscript. We thank the staff at Sukhothai Thammathirat Open University (STOU) who
assisted with student contact, and the STOU students who are participating in the cohort
study. We also thank Dr Bandit Thinkamrop and his team from Khon Kaen University for
guiding us successfully through the complex data processing.
Competing interests
We declare that we have non-financial competing interests.
Contributor statement
The corresponding author had full access to all data used in the study and had final
responsibility for the decision to submit for publication. BT and VY conceptualized the
analysis for this paper with contributions from all authors. BT and VY wrote the first draft.
BT did the literature search and VY did statistical analyses. TK had the initial idea for the
heat stress study. SS and AS conceived and executed the Thai Cohort Study and assisted with
the writing and interpretation. All authors contributed to and approved the final version.
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Reference lists
1. Confalonieri U, Menne B, Akhtar R, Ebi K, Hauengue M, Kovats RS, et al. Human Health. Climate change 2007: Impacts, adaptation and vulnerability, contribution of working group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press; 2007 [cited 2012 13 March]; Available from: http://www.ipcc-wg2.org
2. Basu R, Samet JM. Relation between elevated ambient temperature and mortality: A review of the epidemiologic evidence. Epidemiol Rev. 2002;24(2):190-202.
3. Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41-55.
4. Basu R. High ambient temperature and mortality: A review of epidemiologic studies from 2001 to 2008. Environ Health. 2009;8(40).
5. Bi P, Williams S, Loughnan M, Lloyd G, Hansen AL, Kjellstrom T, et al. The effects of extreme heat on human mortality and morbidity in Australia: Implications for public health. Asia Pac J Public Health. 2011;23(2 Suppl):27S-36S.
6. Campbell-Lendrum D, Corvalan C. Climate change and developing-country cities: implications for environmental health and equity. J Urban Health. 2007;84(1 Suppl):i109-17.
7. Parsons K. Human thermal environments: the effects of hot, moderate, and cold environments on human health, comfort and performance. 2nd ed. London: Taylor & Francis; 2003.
8. Kjellstrom T. Climate change, direct heat exposure, health and well-being in low and middle-income countries. Glob Health Action. 2009;2:1-3.
9. Berry HL, Bowen K, Kjellstrom T. Climate change and mental health: a causal pathways framework. Int J Public Health. 2010;55(2):123-32.
10. Tawatsupa B, Lim LL-Y, Kjellstrom T, Seubsman S, Sleigh A, the Thai Cohort Study team. The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers. Glob Health Action. 2010;3(5034).
11. Hancock PA, Ross JM, Szalma JL. A meta-analysis of performance response under thermal stressors. Hum Factors. 2007;49(5):851-77.
12. Kjellstrom T. Climate change exposures, chronic disease and mental health in urban populations:a threat to health security, particularly for the poor and disadvantaged. Kobe, Japan: World Health Organization Centre for Health and Development; 2009.
Page 19 of 31
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J Open: first published as 10.1136/bm
jopen-2012-001396 on 6 Novem
ber 2012. Dow
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For peer review only
Tawatsupa Page 20
13. Kjellstrom T, Holmer I, Lemke B. Workplace heat stress, health and productivity - an increasing challenge for low and middle-income countries during climate change. Glob Health Action. 2009;2.
14. Kjellstrom T, Gabrysch S, Lemke B, Dear K. The "Hothaps" program for assessing climate change impacts on occupational health and productivity: an invitation to carry out field studies Glob Health Action. 2009;2.
15. Limsakul A, Goes JI. Empirical evidence for interannual and longer period variability in Thailand surface air temperatures. Atmos Res. 2008;87(2):89-102.
16. Thai Meteorological Department. Climate change in Thailand for last 52 years. Bangkok: Meteorological Department, Thailand; 2007 [4 February 2012]; Available from: http://www.tmd.go.th/info/info.php?FileID=86.
17. Langkulsen U, Vichit-Vadakan N, Taptagaporn S. Health impact of climate change on occupational health and productivity in Thailand. Glob Health Action. 2010;3(5607).
18. McMichael AJ, Wilkinson P, Kovats RS, Pattenden S, Hajat S, Armstrong B, et al. International study of temperature, heat and urban mortality: the 'ISOTHURM' project. Int J Epidemiol. 2008 Oct;37(5):1121-31.
19. Pudpong N, Hajat S. High temperature effects on out-patient visits and hospital admissions in Chiang Mai, Thailand. Sci Total Environ. 2011;409:5260–7.
20. Tawatsupa B, Lim LL-Y, Kjellstrom T, Seubsman S, Sleigh A, the Thai Cohort Study team. Association between occupational heat stress and kidney disease among 37,816 workers in the Thai Cohort Study (TCS). J Epidemiol. 2012;22.
21. Sleigh A, Seubsman S, Bain C. Cohort profile: The Thai Cohort of 87,134 Open University students. Int J Epidemiol. 2008 Apr;37(2):266-72.
22. Grad FP. The Preamble of the Constitution of the World Health Organization. Bull World Health Organ. 2002;80(12):981-4.
23. Cummins RA, Eckersley R, Pallant J, van Vugt J, Misajon R. Developing a National Index of Subjective Wellbeing: The Australian Unity Wellbeing Index. Soc Indic Res. 2003;64(2):159-90.
24. Yiengprugsawan V, Seubsman S, Khamman S, Lim LL-Y, Sleigh A, the Thai Cohort Study Team. Personal wellbeing index in a national cohort of 87,134 Thai adults. Soc Indic Res. 2010;98(2):201-15.
25. StataCorp. Stata 12.0 for Windows. College Station TX: StataCorporation; 2011.
Page 20 of 31
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
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j.com/
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J Open: first published as 10.1136/bm
jopen-2012-001396 on 6 Novem
ber 2012. Dow
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For peer review only
Tawatsupa Page 21
26. Kanazawa M, Yoshiike N, Osaka T, Numba Y, Zimmet P, Inoue S. Criteria and classification of obesity in Japan and Asia-Oceania Asia Pac J Clin Nutr. 2002;11:S732-S7.
27. Hajat S, O'Connor M, Kosatsky T. Health effects of hot weather: from awareness of risk factors to effective health protection. Lancet. 2010;375(9717):856-63.
28. McMichael AJ, Woodruff RE, Hales S. Climate change and human health: present and future risks. Lancet. 2006;367(9513):859-69.
29. Kjellstrom T, Butler AJ, Lucas RM, Bonita R. Public health impact of global heating due to climate change: potential effects on chronic non-communicable diseases. Int J Public Health. 2010;55:97-103.
30. Lan L, Lian Z, Pan L. The effects of air temperature on office workers’ well-being, workload and productivity-evaluated with subjective ratings. Appl Ergon. 2010;42(1):29-36.
31. Anderson C. Heat and violence. Curr Dir Psychol Sci. 2001;10(1):33-8.
32. Nitschke M, Tucker GR, Bi P. Morbidity and mortality during heatwaves in metropolitan Adelaide. Med J Aust. 2007;187(11):662-5.
33. Hansen AL, Bi P, Nitschke M, Ryan P, Pisaniello D, Tucker G. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect. 2008;116(10):1369 - 75.
34. Anderson C, Anderson K, Dorr N, DeNeve K, Flanagan M. Temperature and aggression Adv Experimental Social Psychology. 2000;32:63-133.
35. Cheatwood D. The effects of weather on homicide. J Quant Criminol. 1995;11(1):51-70.
36. Maes M, De Meyer F, Thompson P, Peeters D, Cosyns P. Synchronized annual rhythms in violent suicide rate, ambient temperature and the light-dark span. Acta Psychiatr Scand. 1994 Nov;90(5):391-6.
37. Bouchama A, Dehbi M, Mohamed G, Matthies F, Shoukri M, Menne B. Prognostic factors in heat wave-related deaths: A meta-analysis. Arch Intern Med. 2007;167(20):2170-6.
38. Guo Y, Punnasiri K, Tong S. Effects of temperature on mortality in Chiang Mai city, Thailand: a time series study. Environ Health. 2012;11(1):36.
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Response to Decision Letter to BMJ Open
Date: 20/07/12
Manuscript ID: bmjopen-2012-001396
Title: "Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults"
Dear Managing Editor, BMJ Open
I have completed the revised manuscript "Heat stress, health, and wellbeing: findings from a large
national cohort of Thai adults" (Manuscript ID: bmjopen-2012-001396)
I would like to resubmit this revised version of the manuscript. The changes in the manuscript were
indicated by using red font color. We have also responded to the reviewers’ comments and
suggestions in this document, reproducing in indented paragraphs the red font manuscript
revisions and explaining in blue font how each point is addressed and why we responded as we
did.
Response to Reviewer comments
1. Reviewer: Prof. Yuk Yee Yan (Department of Geography, Hong Kong Baptist University
Kowloon Tong, Hong Kong)
1) The study examined the impact of heat stress in the hot season in Thailand. When is the hot
season in Thailand? What are the maximum, mean, minimum temperatures and relative humidity?
Is there any spatial variations? I would suggest the authors to have a brief description of the
climate in Thailand.
We have added information of climate in Thailand in the Introduction section (4th paragraph)
in Page 5.
“…In tropical Thailand, hot and humid conditions are common, especially in the hot season
(March - June). The monthly maximum, mean and minimum temperatures averaged from
1999 to 2008 were around 33°C, 27°C, and 22°C respectively with the averaged relative
humidity at 75%. The monthly maximum temperatures averaged during ten years varied
little by region (32-33°C) and were highest in the North region during April (40°C) and
lowest in the same region during December (24°C) (Tawatsupa et al., 2012a)..”
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2) The subjects of the study came from all areas of Thailand. Were the subjects evenly distributed
geographically (i.e. were the number of subjects from various parts of Thailand the same)? If there
is geographical variations in climate, responses of the subjects may also be different. I would like
the authors to address these questions.
Regarding our response to comments No. 1, the monthly maximum temperature averaged
during 1999 to 2008 varied little by geographical region (32-33°C). We are also aware of the
responses to heat stress of subjects in different area of Thailand. Here (for this response to item 2)
we did additional analysis to show the number of study population, number of respondents and %
prevalence of often heat interference daily activities by region of Thailand (Table A, below – not for
inclusion in the paper). We also added a sentence in the Result section (2nd paragraph) in page 9;
“…We noted that the prevalence of ‘often’ heat interference for each daily activity are not
much different in different regions (33-42% for daily travel, 29-38% for work, 26-32% for
housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat
interference frequency categories are summarized in Table 2.…”
Table A. Study population, and % prevalence of ‘often’ heat interference daily activities by
region of Thailand.
Daily activities Bangkok Central North Northeast South Total
Total N 10,310 15,349 11,329 15,912 7,668 60,569 Often heat interference
Sleeping N 2,638 4,243 3,267 4,462 1,729 16,339 % 26.0 28.1 29.3 28.6 23.0 27.4
Housework N 2,903 4,634 3,525 4,787 1,922 17,771 % 28.7 30.8 31.7 30.7 25.6 29.9
Daily travel N 4,283 5,886 3,972 5,635 2,515 22,291 % 42.3 39.1 35.7 36.2 33.5 37.5
Work N 2,970 5,080 4,132 5,891 2,408 20,481 % 29.4 33.7 37.1 37.8 32.0 34.5
Exercise N 2,371 3,800 3,105 4,427 1,690 15,393 % 23.5 25.3 27.9 28.4 22.5 25.9
.------------------------------------------
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2. Reviewer: Prof. S. Tong (School of Public Health and Social Work, Institute of Health and
Biomedical Innovation, Queensland University of Technology, AUSTRALIA)
1) About one third of the participants were lost to follow-up in 2009 and what is the potential for
loss to follow-up bias? A table should be provided to compare the characteristics of the participants
and those who were lost to follow-up in 2009.
To respond to this item 1, we have prepared a table comparing overall socio-demographic
and health characteristics of the 60,569 cohort members followed up in 2009 and those 26,578
participants who lost to follow-up (Table B). It is not necessary to include this table and we have
started the Results (in Page 8) with the following inserted sentence.
“…We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not
shown). The two groups were similar for age, sex ratio, employment, income, and health
outcomes studied here (energy levels, emotional problems, life satisfaction)…”
Table B. Socio-demographic and health characteristics in 2005 of Thai cohort member in the follow-up group and who loss in the 2009
Cohort characteristics in 2005 Cohort members in 2005&2009
Participants only in 2005
Total
Total N 60,569 26,578 87,174
Sex
Male 45.3 45.5 45.3
Female 54.7 54.5 54.7
Personal monthly incomes
<= 3000 9.5 14.6 11.0
3001-7000 28.7 36.1 30.9
7001-10000 23.4 23.0 23.3
10001-20000 26.5 18.8 24.2
20001-30000 7.2 4.1 6.3
>30000 4.7 3.4 4.3
Work for income
Yes 88.4 82.4 86.5
No 11.7 17.7 13.5
Energy levels in the past 4 weeks
Very much 17.4 17.5 17.4
Quite a lot 42.7 42.0 42.5
Some 30.0 29.8 30.0
A little or none 9.9 10.8 10.2 Emotional problems in the past 4 weeks
Not at all 10.9 8.9 10.3
Slightly 53.0 49.2 51.9
Moderately 21.9 24.3 22.6
Quite a lot / extremely 14.2 17.6 15.2
Overall life satisfaction
9-10 very satisfied (highest) 31.7 29.3 31.0
8 (high) 28.7 26.8 28.1
6-7 (medium) 25.9 26.5 26.1
0-5 not very satisfied (low) 13.7 17.4 14.9
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2) More details are needed for the Methods section. For instance, it is unclear how valid the
questions used in the survey instrument are. They stated that “Questions related to heat stress
were as follows: “How often did the hot period this year interfere with the following activities? 1)
sleeping; 2) housework…” However, there is no description about how they defined the
interference. It could lead to over- or/and under-estimates of heat impacts if the definition is
unclear.
We added a sentence describing the definition of heat interference (in Methods section,
under Measures of heat stress, page 7). Also, we now have a validation study for heat stress
question by calling back to the heat stress respondents in 2009. The preliminary results show that
heat stress data are valid and useful to publish with the analysis and caveats as produced for this
paper submitted to BMJOpen.
“…Questions related to heat stress were as follows: “How often did the hot period this year
interfere with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work;
and 5) exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times
per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means
heat stress causing an uncomfortable feeling when doing those daily activities. For
analysis, we grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per
month), and ‘often’ (1-6 times per week or every day)….”
3) Similarly, it may be unreliable for just using two questions from SF8 to measure the physical and
mental health impacts of heat. Discussion should be expanded.
We expanded the 3rd paragraph of the Discussion (in page 11), including…..
“…Elsewhere we have completed detailed analyses of associations between heat stress
and self-reported health outcomes in the cohort using the questions from SF8 (Tawatsupa
et al., 2010). Our studied outcomes in this report were holistic fundamental measures of
health…..”
4) Some relevant studies have already been conducted in Thailand (e.g., refs 10, 18-20 and Guo
et al, 2012), and the authors should discuss if their results are consistent with previous findings,
even though different studies focused on different health outcomes.
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5
We added one paragraph in the Discussion section (6th Paragraph) in page 12.
“…In our study, we found that heat stress in Thailand is not only a problem at work but also
heat stress interferes with other daily activities including sleeping, daily travel, housework
and exercise. The results of our study complement other Thai research about adverse
effects of heat. One recent report shows that heat stress in Thailand is a very serious
problem in a wide variety of work settings (Langkulsen et al., 2010). McMichael et al (2008)
and Guo et al (2012) found a temperature–mortality association and Pudpong et al (2011)
found heat related excess hospital admissions. Worker studies in Thailand related
occupational heat stress, kidney disease and psychological distress (Tawatsupa et al.,
2010, Tawatsupa et al., 2012b)…”
.------------------------------------------
3. Reviewer: Patrizia Schifano
1) The study is a cross-sectional study, based on a self administered questionnaire. The
questionnaire contains questions on "perception of the effect of heat on daily activities" and on
health outcomes. I would suggest to reformulate the objective of the paper, specifying they are
measuring the association between the perceived interference of heat stress on daily activities and
health outcomes. No direct measure of the exposure is taken.
Here, we added the word “self-reported” for heat stress interference in the objective of the
Abstract (Page 2).
“…Objectives: This study aims to examine the association between self-reported hot
season heat stress interference with daily activities (sleeping, work, travel, housework,
exercise) and three graded holistic health and wellbeing outcomes (energy, emotions, life
satisfaction)…”
And in the Article summary (Page 3)
“…To examine the association between self-reported heat stress interference with daily
activities (sleeping, work, travel, housework, exercise) during hot season and three graded
holistic health outcomes (energy, emotions, life satisfaction) in Thailand..”
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6
2) Furthermore the question on the interference between heat stress and daily activity is referred to
the whole year. Why didn't they restrict the reference period to the hot season? Alternatively they
could have repeated the question referring it separately to the hot season and the cold
season. Also questions revealing the health status are referred to a different period (one is referred
to the all-life time period, and the other two to the last month, and we don't know if this "last month"
was in the hot season or not. Assuming that heat stress can influence the perception of their
status, this might be important.
As we mentioned in the Methods (page 5) and Discussion section (page 11) that the heat
stress and health outcomes questions were in different parts of questionnaire, the respondents
could not easily link in their mind so answers on these issues were independent.
For heat stress question, we do not have detailed information on the date or season when
respondents answered the questions as our cohort data were collected by mailing continuously
during the year of study (in 2009). Although, the heat stress question did refer specifically to the
hot period within that year, tropical Thailand in general has hot and humid weather almost all year
round and not much variation within a year. We believe that the self-reported heat stress can give
information on frequency of heat interference during the study period (times per month or week).
For the health outcome measurements, the reason to use the period of past four weeks is to
prevent the recall-bias of self-reported health outcomes. In this study, the period of the past four
weeks was used according to the standard Medical Outcomes Short Form Instrument (SF8). Thus,
it would be complex to classify in more detail of hot and cold season and our baseline
questionnaire was very broad and was 20 pages long. We have done our best to utilise and
classify the heat stress related information gathered.
3) It is well known that some subjects are more susceptible than others to heat. In many studies
the elderly represents the part of the population more susceptible to the negative effect of heat on
health. The studied cohort is composed mainly by very young. This should be stressed more in the
paper.
This is a very helpful point. Our results showed heat stress and health impacts in a national
group of young and middle-aged Thai adults. We are aware that age effects heat stress and health
outcomes relationships so age was considered as a confounder in our analysis. Here we added a
sentence in the Abstract (page 2) and Discussion section (last paragraph in page 13) showing our
concern about heat stress effects in the elderly in the future;
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“…We conclude that Thai populations are at high risk of heat stress during daily activities.
Also, in Thailand an anticipated increase in temperature from climate change plus the
ageing and urbanisation of the population could significantly increase heat impacts on
health and wellbeing. There is a need for improvements in public health surveillance and
public awareness regarding the risks of heat stress which hitherto have been considered
unremarkable in such a tropical environment.”
-----------------------------------
Reference
Guo, Y., Punnasiri, K. & Tong, S. 2012. Effects of temperature on mortality in chiang mai city, thailand: A
time series study. Environmental Health, 11, 36.
Langkulsen, U., Vichit-Vadakan, N. & Taptagaporn, S. 2010. Health impact of climate change on
occupational health and productivity in thailand. Global Health Action, 3. DOI:10.3402/gha.v3i0.5607.
Mcmichael, A. J., Wilkinson, P., Kovats, R. S., Pattenden, S., Hajat, S., Armstrong, B., Vajanapoom, N.,
Niciu, E. M., Mahomed, H., Kingkeow, C., Kosnik, M., O'neill, M. S., Romieu, I., Ramirez-Aguilar, M.,
Barreto, M. L., Gouveia, N. & Nikiforov, B. 2008. International study of temperature, heat and urban
mortality: The 'isothurm' project. International Journal of Epidemiology, 37, 1121-31.
10.1093/ije/dyn086.
Pudpong, N. & Hajat, S. 2011. High temperature effects on out-patient visits and hospital admissions in
chiang mai, thailand. Science of the Total Environment, 409, 5260–5267.
10.1016/j.scitotenv.2011.09.005.
Tawatsupa, B., Dear, K., Kjellstrom, T. & Sleigh, A. 2012a. The association between temperature and
mortality in tropical middle income thailand from 1999 to 2008. Canberra: National Centre for
Epidemiology and Population Health.
Tawatsupa, B., Lim, L. L.-Y., Kjellstrom, T., Seubsman, S., Sleigh, A. & The Thai Cohort Study Team 2010.
The association between overall health, psychological distress, and occupational heat stress among
a large national cohort of 40,913 thai workers. Global Health Action, 3. 10.3402/gha.v3i0.534.
Tawatsupa, B., Lim, L. L.-Y., Kjellstrom, T., Seubsman, S., Sleigh, A. & The Thai Cohort Study Team 2012b.
Association between occupational heat stress and kidney disease among 37,816 workers in the thai
cohort study (tcs). Journal of Epidemiology, 22. 10.2188/jea.JE20110082.
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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cross-sectional studies
Section/Topic Item
# Recommendation Reported on page #
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 2
(b) Provide in the abstract an informative and balanced summary of what was done and
what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 4
Objectives 3 State specific objectives, including any prespecified hypotheses 5
Methods
Study design 4 Present key elements of study design early in the paper 7
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
5
Participants
6
(a) Give the eligibility criteria, and the sources and methods of selection of participants 5
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
6
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of assessment
(measurement). Describe comparability of assessment methods if there is more than
one group
6
(Our heat exposed group include respondents who
reported heat interfere their daily activities at 1-6 times
per week or every day. An unexposed group include
those who reported never experienced heat or 1-3 times
per month)
Bias 9 Describe any efforts to address potential sources of bias 6
Study size 10 Explain how the study size was arrived at 8
Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe
which groupings were chosen and why
7
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 7
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(b) Describe any methods used to examine subgroups and interactions 7
(c) Explain how missing data were addressed 8
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study, completing
follow-up, and analysed
8
(b) Give reasons for non-participation at each stage -
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
8
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures 9
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders were
adjusted for and why they were included
9
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity
analyses
10
Discussion
Key results 18 Summarise key results with reference to study objectives 10
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
11
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
11
Generalisability 21 Discuss the generalisability (external validity) of the study results 11
Other information
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Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
17
*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
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Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults
Journal: BMJ Open
Manuscript ID: bmjopen-2012-001396.R2
Article Type: Research
Date Submitted by the Author: 03-Oct-2012
Complete List of Authors: Tawatsupa, Benjawan; Health Impact Assessment Division, Department of Health; National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology and Environment Yiengprugsawan, Vasoonatara; The Australian National University, National Centre for Epidemiology and Population Health Kjellstrom, Tord; Centre for Global Health Research, Umeå University; The Australian National University, National Centre for Epidemiology and Population Health Seubsman, Sam-ang; Sukhothai Thammathirat Open University, School of Human Ecology Sleigh, Adrian; The Australian National University, National Centre for Epidemiology and Population Health
<b>Primary Subject Heading</b>:
Occupational and environmental medicine
Secondary Subject Heading: Epidemiology, Public health
Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, EPIDEMIOLOGY, Epidemiology < TROPICAL MEDICINE
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Heat stress, health, and wellbeing: findings from a large
national cohort of Thai adults
Benjawan Tawatsupa1, 2,*, Vasoontara Yiengprugsawan1, Tord Kjellstrom1, 3,
Sam-ang Seubsman4, Adrian Sleigh1, and the Thai Cohort Study Team
1 National Centre for Epidemiology and Population Health, ANU College of Medicine,
Biology and Environment, the Australian National University, Canberra, Australia
2 Health Impact Assessment Division, Department of Health, Ministry of Public Health,
Nonthaburi, Thailand
3 Centre for Global Health Research, Umeå University, Umeå, Sweden
4 School of Human Ecology, Sukhothai Thammathirat Open University, Nonthaburi, Thailand
*Corresponding author:
Benjawan Tawatsupa,
The Australian National University
Building 62 – NCEPH, Mills Rd, 0200, Canberra, Australia
Email [email protected], [email protected]
Tel: +61 2 6125 5615; Fax: +61 2 6125 0740
The Thai Cohort Study Team
Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn,
Suwanee Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol,
Janya Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai
Somboonsook, Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun,
Wanee Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell,
Bruce Caldwell, Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David
Harley, Matthew Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony
McMichael, Tanya Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara
Yiengprugsawan.
Keywords: Heat stress, health, wellbeing, Thailand Word count: 2,757 words
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Abstract
Objectives: This study aims to examine the association between self-reported heat stress
interference with daily activities (sleeping, work, travel, housework, exercise) and three
graded holistic health and wellbeing outcomes (energy, emotions, life satisfaction).
Design: A cross-sectional study.
Setting: The setting is tropical and developing countries as Thailand, where high temperature
and high humidity are common, particularly during the hottest seasons.
Participants: This study is based on an ongoing national Thai Cohort Study of distance-
learning open-university adult students (N=60,569) established in 2005 to study the health-
risk transition.
Primary and secondary outcome measures: Health impacts from heat stress in our study
are categorized as physical health impacts (energy levels), mental health impacts (emotions),
and wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds
Ratios (ORs) and 95% confidence intervals using multinomial logistic regression adjusting
for a wide array of potential confounders.
Results: Negative health and wellbeing outcomes (low energy level, emotional problems,
and low life satisfaction) associated with increasing frequency of heat stress interfering with
daily activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and
in general worse than energy level (between 1·31 and 2·91), and life satisfaction (between
1·10 and 2·49). The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
Conclusions: In tropical Thailand there already are substantial heat stress impacts on health
and wellbeing. Increasing temperatures from climate change plus the ageing and urbanisation
of the population could significantly worsen the situation. There is a need to improve public
health surveillance and public awareness regarding the risks of heat stress in daily life.
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Article summary
• Article focus:
o To examine the association between self-reported heat stress interference with
daily activities (sleeping, work, travel, housework, exercise) during hot season
and three graded holistic health outcomes (energy, emotions, life satisfaction)
in Thailand.
• Key messages:
o Negative health and wellbeing outcomes (low energy level, emotional
problems, and low life satisfaction) associated with increasing frequency of
heat stress interfering with daily activities.
o The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
o The results from this study point to the need for improving public health
surveillance and public awareness regarding the risks of heat stress in daily life
in a tropical country like Thailand.
• Strengths and limitations of this study:
o The possible limitation of self-reports, but note that questions on heat stress
and health outcomes were in different parts of the questionnaire.
o The strength of this study is its large scale with participation from a national
group of adults embedded in the socioeconomic mainstream of Thai society
and used the comprehensive questionnaire which captures a detailed
assessment of health and an array of geodemographic, environmental and
social attributes.
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Introduction
Over the last decade interest has grown in the impact of global warming on human health.(1)
Increasing heat stress has substantial adverse effects on population mortality and
morbidity.(2-5) This information is from developed and temperate countries(3) and leaves
unanswered questions for tropical and developing countries where high temperature and
humidity are common. Furthermore, heat stress in tropical cities is increasing due to urban
heat island effects caused by industrial development and urbanisation in developing
countries.(6)
Heat stress can have a major influence on daily human activities. The body absorbs external
heat due to high air temperature and humidity, low air movement, and high solar radiation; as
well, some physical activities generate heat internally.(7) Excess heat exposure during normal
daily activities creates a high risk of recurrent dehydration and can cause other effects on
physical health (eg, exhaustion, heat cramps, heat stroke, or death).(7) Heat stress affects
mood, increases psychological distress and mental health problems,(8-10) and also reduces
key human psychological performance variables.(11)
Other heat stress impacts may arise from increased mistakes in daily activities and accidental
injuries. As well, disturbed sleep and degraded physical performance from heat exhaustion
reduce work capacity and lead to loss of income.(8, 12-13) Populations at risk of heat stress
are not only the elderly but also young people and adults who are more likely to carry out
heavy labour outdoors or work indoors without air conditioning or other effective cooling
systems during the hot season.(8, 12, 14)
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In tropical Thailand, hot and humid conditions are common, especially in the hot season
(March - June). The monthly maximum, mean and minimum temperatures averaged from
1999 to 2008 were around 33°C, 27°C, and 22°C respectively with the averaged relative
humidity at 75%. The monthly maximum temperatures averaged during ten years varied little
by region (32-33°C) and were highest in the North region during April (40°C) and lowest in
the same region during December (24°C).(Tawatsupa et al, unpublished data, 2012)
Global warming (or “global heating” may be a better description in relation to Thailand) is
now causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the
monthly mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean
minimum temperature increased even more at 1·44 ˚C.(15) Heat stress is already a concern in
Thailand and the observed trends indicate further increase in air temperature.(16) A recent
study of occupational heat stress in Thailand by Langkulsen et al(17) revealed a very serious
problem (“extreme caution” or “danger”) in an array of work settings (they tested a pottery
factory, a power plant, a knife manufacture site, a construction site and an agricultural site).
Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities
(18-19) and for workers.(10, 20) However, there is no available information on how much
heat interferes with normal daily activities and heat stress effects on health and well-being in
the general Thai population. Here we report an investigation of association between heat
stress interference with daily activities and health and wellbeing in a large national cohort of
young and middle aged Thai adults.
Methods
Study population
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In 2005, a baseline questionnaire was mailed out to adult students enrolled at Sukhothai
Thammathirat Open University (STOU). The questionnaire was developed by a multi-
disciplinary team in both Thailand and Australia to cover a wide range of topics for a
longitudinal study of the Thai Health-Risk Transition – transformation of the health-risk and
outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge.
Overall, 87,134 distance learning students aged 15 to 87 years responded from all areas of
Thailand. Cohort participants were generally similar to the population of Thailand, especially
in the 30-39 years age group, for sex ratio, income and geographical location.(21)
Data collected included demographic, socioeconomic and geographic characteristics, physical
and mental health status, personal wellbeing, health service use, risk behaviors, injuries, diet,
physical activity, and family background. A four-year follow-up was conducted in 2009 and
the next one is due in 2013.
This report is based on the 2009 follow-up which included questions on heat interference with
normal daily activities. The heat stress and health outcome measures (both described below)
were in different parts of the questionnaire. They could not easily be linked in the respondents
mind so answers on these issues were independent. Covariates analyzed are described with
the results and include age, sex, marital status, geographic location, work status, smoking,
drinking, and Body Mass Index.
Measures of heat stress
Questions related to heat stress were as follows: “How often did the hot period this year
interfere with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work;
and 5) exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times
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per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means heat
stress causing an uncomfortable feeling when doing those daily activities. For analysis, we
grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per month), and ‘often’
(1-6 times per week or every day).
Measures of health and wellbeing outcomes
Health is defined by World Health Organization (WHO) as “a complete state of physical,
mental, and social wellbeing and not merely the absence of disease or infirmity”.(22) Health
impacts from heat stress in our study are categorized as physical health impacts (eg, energy
levels), mental health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three
outcomes were selected because they match the holistic WHO health definition and represent
fundamental health states. Many other more specific diseases would be expected to follow
adverse outcomes for these health measures (see Discussion).
To measure the physical and mental health impacts we used two questions from the standard
Medical Outcomes Short Form Instrument (SF8) as follows: Energy: “During the past four
weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’,
‘a little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the
past four weeks, how much have you been bothered by emotional problems (such as feeling
anxious, depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite
a lot’, and ‘extremely’. For analysis the last two categories were combined. To measure
Wellbeing we used a standardised question:(23-24) “Thinking about your own life and
personal circumstances, how satisfied are you with your life as a whole?” Scores range from 0
(‘completely dissatisfied’) to 10 (‘completely satisfied’).
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Data processing and statistical analysis
Data scanning and editing involved checking the actual questionnaire response against its
digital value using Thai Scandevet, SQL and SPSS software. For analysis we used
multinomial logistic regression reporting odds ratios (adjusted for potential confounders)
based on Stata version 12.(25) For all three fundamental health outcomes (energy, emotions,
wellbeing), the multinomial regression estimates the odds with which each of three
increasingly severe abnormalities occurs relative to the odds of an optimal outcome.
Individuals with missing data were excluded so totals presented vary a little according to
information available.
Ethical considerations
Ethics approval was obtained from Sukhothai Thammathirat Open University Research and
Development Institute (protocol 0522/10) and the Australian National University Human
Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from
all participants.
Results
We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not shown).
The two groups were similar for age, sex ratio, employment, income, and health outcomes
studied here (energy levels, emotional problems, life satisfaction). Socio-demographic and
health characteristics of the 60,569 cohort members followed up in 2009 are presented in
Table 1. There were slightly more females (54·8%), 70% were aged less than 40 years, and
55·3% were married. Nearly 20% reported household monthly income of less than 10,000
Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban areas.
Health risk behaviors - regular smoking or regular alcohol drinking -were reported by 7·7%
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and 13·7%, respectively. By Asian standards,(26) half the cohort members were in the normal
weight range, 9·5% were underweight, 18·8% were overweight, and 22·1% were obese.
We noted that prevalence of ‘often’ heat interference for each daily activity are not much
different in different regions of Thailand (33-42% for daily travel, 29-38% for work, 26-32%
for housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat
interference frequency categories are summarized in Table 2. Heat interference ‘often’ was
reported (in order of frequency) by 37·5% for daily travel, 34·5% for work, 29·9% for
housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing frequency
outcomes are reported in Table 3: 37·6% reported being very satisfied with their life, around
15% reported having very much energy in the past 4 weeks and close to 11% reported no
emotional problems in the past 4 weeks.
Daily activities show a clear trend connecting increasing heat interference with worse health
and wellbeing (Table 4). For example, cohort members who experienced heat interference
‘often’ while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently
than ‘no’ emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was
found for those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the
same trend was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have
also shown strong gradients connecting frequent heat interference and worse health outcomes.
The multinomial logistic regression, adjusting for a wide array of potential confounders (see
footnote for Table 5), supported the descriptive results. For all three health outcomes, when
each of the three graded adverse outcome categories is compared to the optimal outcome, the
relative odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for
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each health outcome, more heat interference associates more strongly with a given grade of
abnormality). And 95% confidence intervals for all odds ratios indicated statistical
significance. So heat stress interfering with normal daily activities (sleep, housework, travel,
work, exercise) associates with adverse outcomes for all three holistic measures of health. For
example, reporting heat interference ‘often’ while sleeping was strongly associated with ‘little
or none’ energy [OR = 2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81,
95% CI 4·32-5·36] and ‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work,
reporting heat interference ‘often’ was associated with ‘little or none’ energy [OR = 2·45,
95% CI 2·22-2·71] and ‘extreme’ emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar
results were found during daily travel and doing housework. A statistically significant
association was also found for heat inference during exercise but the magnitude of the effect
was lower than for other activities.
Discussion
Our study shows that climate-related heat stress in tropical Thailand associated with self-
reported health and wellbeing if the heat interfered with daily activities such as sleep,
housework, travel, work, and exercise. The large study group included young and middle-age
Thai adults, mostly doing paid work, with a little over half residing in urban areas. These
cohort members are active and over 20% report often experiencing heat interference for daily
activities during the hot season. Daily travel and work were sources of heat stress more often
than other activities, probably because they involve time spent in traffic or outdoors during
hot periods. Other activities such as housework have less heat stress than daily travel and
work, perhaps because these activities are home-based where air-conditioning or other
ventilation is available.
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We found those who report higher levels of heat stress interference with daily activities tend
to also be the ones who have adverse health and wellbeing outcomes (low life satisfaction,
low energy level, and worse emotional problems). Odds Ratios of heat stress effects across all
daily activities for emotional problems are between 1·55 and 4·81 and in general are worse
than energy level effects (between 1·31 and 2·91) and life satisfaction effects (between 1·10
and 2·49). The worst health outcomes were for heat stress while sleeping followed by heat
stress for daily travel, work, housework and exercise.
Our data are based on self-report by educated Thais and we note that questions on heat stress
and health outcomes were in different parts of the questionnaire. Findings show strong and
highly consistent trends especially for adverse health effects of frequent heat interference
during sleep, daily travel, and work. Elsewhere we have completed detailed analyses of
associations between heat stress and self-reported health outcomes in the cohort using the
questions from SF8 (10). Our studied outcomes in this report were holistic fundamental
measures of health. We can expect that those who had abnormal findings would also (already
or eventually) manifest other more specific chronic diseases such as depression, obesity,
hypertension, and kidney disease. If so, the eventual burden of heat-related disease will be
higher than currently recognized.(27-29)
Our findings add to some previous reports on working in hot environments which found that
heat stress significantly reduced people’s motivation to do their work. Lan et al (30) assessed
office workers’ perceptions of thermal environment, emotions, well-being, and motivation to
work, and found that participants had lower motivation to work and experienced more
negative moods in hot environments. Anderson found that the prolonged, continuous
repetitive actions required to maintain performance at work and achieve target goals (such as
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getting a job finished) can lead to hypertension.(31) And when more effort was required to
complete a task in hot conditions loss of motivation was experienced leading to lower
productivity and increased injury risk. The impact of heat stress on psychological
performance variables (11) is a likely factor in these work related impacts of heat.
Psychological effects of heat stress have been noted in other settings as well. Nitschke et al
(32) reported a positive association between high ambient temperature and hospital
admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses for
which admissions increased included anxiety, symptomatic mood disorders, and
psychological development disorders among elderly people when temperature exceeded
26·7°C.(33) Moreover, excessive heat stress exposure may also increase violence.(31-34)
Increasing heat stress had been associated with higher rates of aggressive behavior,(35) and
higher violent suicide rates.(36) In a meta-analysis, Bouchama et al (37) concluded that pre-
existing mental health problems tripled the risk of all-cause mortality during a heat wave. A
related issue is the physical and psychological exhaustion caused by extreme heat stress. (7)
In our study, we found that heat stress in Thailand is not only a problem at work but also heat
stress interferes with other daily activities including sleeping, daily travel, housework and
exercise. The results of our study complement other Thai research about adverse effects of
heat. One recent report shows that heat stress in Thailand is a very serious problem in a wide
variety of work settings (17). McMichael et al (18) and Guo et al (38) found a temperature–
mortality association and Pudpong et al (19) found heat related excess hospital admissions.
Worker studies in Thailand related occupational heat stress, kidney disease and psychological
distress.(10, 20)
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One limitation of this study is that it could not directly establish that health and wellbeing
outcomes arose as a result of heat stress. Interpreting causality between heat stress exposure
and health and wellbeing outcomes is complex in a cross-sectional study as we cannot be
completely sure that heat stress preceded their health condition and wellbeing. Also, the
source of the heat stress was not reported and we could not make direct measurements of heat
stress exposure and health and wellbeing outcomes. Another limitation of this study arose
because people answered the questionnaire at different times of the year (but most in March to
July - the hot period). The questions on physical and emotional health assessed the previous
four weeks so most (almost all) were answering for the hot period.
The strength of this study is its large scale with participation from a national group of adults
embedded in the socioeconomic mainstream of Thai society. Other strengths include the
comprehensive questionnaire which captures a detailed assessment of health and an array of
geodemographic, environmental and social attributes. Also, the cohort has been set up for
future longitudinal analysis which will provide better insight into causal pathways between
heat stress and subsequent health outcomes in the long run.
We conclude that Thai populations are at high risk of heat stress during daily activities. Also,
in Thailand an anticipated increase in temperature from climate change plus the ageing and
urbanisation of the population could significantly increase heat impacts on health and
wellbeing. There is a need for improvements in public health surveillance and public
awareness regarding the risks of heat stress which hitherto have been considered
unremarkable in such a tropical environment.
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Tables
Table 1 Socio-demographic and health characteristics of Thai cohort members in 2009
Cohort characteristics N = 60,569 %
Demographic characteristics
Sex Male 45.3
Female 54.8
Age (year) ≤ 29 27.4
30-39 42.6
40+ 30.0
Marital status Married 55.3
Never married 37.9
Separated, divorced, widowed 6.8
Socio-geographic characteristics
Monthly income (Baht)* ≤10,000 18.8
10,001-20,000 22.4
20,001-30,000 35.7
>30,000 23.1
Work status Doing paid work 73.2
Unpaid family workers 7.3
Seeking work 2.2
Others 17.3
Residence Rural residence 44.0
Urban residence 56.0
Health risk behaviors
Regular smokers 7.7
Regular alcohol drinkers 13.7
Body Mass Index (kg/m2)
Underweight (<18.5) 9.5
Normal (18.5-22.9) 49.5
Overweight at risk (23-24.9) 18.8
Obese (25+) 22.1
*Household monthly income in 2009 (US$ = 35 Baht)
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Table 2 Daily activities and heat interference category among Thai cohort members in 2009
Daily activities
N = 60,569
Heat interference (%)
Not applicable* Never Sometimes Often
Sleeping 15.7 24.3 32.5 27.4
Housework 1.3 37.1 31.7 29.9
Daily travel 3.0 33.7 25.8 37.5
Work 14.0 30.3 21.2 34.5
Exercise 0.8 43.1 30.1 25.9
*Use air conditioner
Table 3 Health and wellbeing outcomes among Thai cohort members in 2009
Outcomes
N = 60,569
%
Overall life satisfaction (score ranged from 0 to 10)
9-10 very satisfied (highest) 37.6
8 (high) 28.8
6-7 (medium) 21.7
0-5 not very satisfied (low) 12.0
Energy level in the past 4 weeks
very much 14.9
quite a lot 44.0
some 32.0
a little or none 9.1
Emotional problems in the past 4 weeks
not at all 11.3
slightly 48.4
moderately 25.8
quite a lot/extremely 14.5
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Table 4 Frequency of heat interference with daily activities by health & wellbeing outcomes among cohort members
Daily activities and
heat interference
category
Health and wellbeing outcomes N=60,569
% Life satisfaction
score ranged from 0 to 10
% Energy level
in the past 4 weeks
% Emotional problems
in the past 4 weeks
9-10
highest
8
high
6-7
medium
0-5
low
very much quite a lot some
little/ none not at all slightly
moderate
extreme
Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)
never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6
sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3
often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9
Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)
never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7
sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4
often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9
Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)
never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2
sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4
often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0
Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)
never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6
sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9
often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7
Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)
never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2
sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9
often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2
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Table 5 Association between heat interference with daily activities and health & wellbeing outcomes among cohort members
Heat
interference
category
N=60,569
Adjusted* Odds Ratios and 95% Confidence Interval
Life satisfaction (score 0-10)** Energy level in the past 4 weeks Emotional problems in the past 4 weeks
high
vs
highest
medium
vs
highest
low
vs
highest
quite a lot
vs
very much
some
vs
very much
little/none
vs
very much
slightly
vs
not at all
moderate
vs
not at all
extreme
vs
not at all
Sleep
never ref ref ref ref ref ref ref ref ref
sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]
often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]
Housework
never ref ref ref ref ref ref ref ref ref
sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]
often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]
Daily travel
never ref ref ref ref ref ref ref ref ref
sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]
often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]
Work
never ref ref ref ref ref ref ref ref ref
sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]
often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]
Exercise
never ref ref ref ref ref ref ref ref ref
sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]
often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]
*Multivariate regression adjusting for potential confounders: age, sex, marital status, work status, household income, urban-rural residence, exercise, housework, hours of
sleep, body mass index, smoking , and drinking
**Life satisfaction scores: highest = 9-10, high = 8, medium = 6-7, low = 0-5
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Acknowledgments
This study was supported by the International Collaborative Research Grants Scheme with
joint grants from the Wellcome Trust UK (GR071587MA) and the Australian National Health
and Medical Research Council (NHMRC 268055), and as a global health grant from the
NHMRC (585426). These funding bodies play no role in the preparation or submission of this
manuscript. We thank the staff at Sukhothai Thammathirat Open University (STOU) who
assisted with student contact, and the STOU students who are participating in the cohort
study. We also thank Dr Bandit Thinkamrop and his team from Khon Kaen University for
guiding us successfully through the complex data processing.
Competing interests
We declare that we have non-financial competing interests.
Contributor statement
The corresponding author had full access to all data used in the study and had final
responsibility for the decision to submit for publication. BT and VY conceptualized the
analysis for this paper with contributions from all authors. BT and VY wrote the first draft.
BT did the literature search and VY did statistical analyses. TK had the initial idea for the
heat stress study. SS and AS conceived and executed the Thai Cohort Study and assisted with
the writing and interpretation. All authors contributed to and approved the final version.
Data Sharing: Statistical code in Stata, and dataset available from the corresponding
author at [email protected]. All Participants gave informed consent and the
presented data in this manuscript are anonymous.
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Reference lists
1. Confalonieri U, Menne B, Akhtar R, et al. Human Health. Climate change 2007: Impacts, adaptation and vulnerability, contribution of working group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press; 2007 [cited 2012 13 March]; Available from: http://www.ipcc-wg2.org
2. Basu R, Samet JM. Relation between elevated ambient temperature and mortality: A review of the epidemiologic evidence. Epidemiol Rev. 2002;24(2):190-202.
3. Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41-55.
4. Basu R. High ambient temperature and mortality: A review of epidemiologic studies from 2001 to 2008. Environ Health. 2009;8(40).
5. Bi P, Williams S, Loughnan M, et al. The effects of extreme heat on human mortality and morbidity in Australia: Implications for public health. Asia Pac J Public Health. 2011;23(2 Suppl):27S-36S.
6. Campbell-Lendrum D, Corvalan C. Climate change and developing-country cities: implications for environmental health and equity. J Urban Health. 2007;84(1 Suppl):i109-17.
7. Parsons K. Human thermal environments: the effects of hot, moderate, and cold environments on human health, comfort and performance. 2nd ed. London: Taylor & Francis; 2003.
8. Kjellstrom T. Climate change, direct heat exposure, health and well-being in low and middle-income countries. Glob Health Action. 2009;2:1-3.
9. Berry HL, Bowen K, Kjellstrom T. Climate change and mental health: a causal pathways framework. Int J Public Health. 2010;55(2):123-32.
10. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers. Glob Health Action. 2010;3(5034).
11. Hancock PA, Ross JM, Szalma JL. A meta-analysis of performance response under thermal stressors. Hum Factors. 2007;49(5):851-77.
12. Kjellstrom T. Climate change exposures, chronic disease and mental health in urban populations:a threat to health security, particularly for the poor and disadvantaged. Kobe, Japan: World Health Organization Centre for Health and Development; 2009.
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13. Kjellstrom T, Holmer I, Lemke B. Workplace heat stress, health and productivity - an increasing challenge for low and middle-income countries during climate change. Glob Health Action. 2009;2.
14. Kjellstrom T, Gabrysch S, Lemke B, et al. The "Hothaps" program for assessing climate change impacts on occupational health and productivity: an invitation to carry out field studies Glob Health Action. 2009;2.
15. Limsakul A, Goes JI. Empirical evidence for interannual and longer period variability in Thailand surface air temperatures. Atmos Res. 2008;87(2):89-102.
16. Thai Meteorological Department. Climate change in Thailand for last 52 years. Bangkok: Meteorological Department, Thailand; 2007 [4 February 2012]; Available from: http://www.tmd.go.th/info/info.php?FileID=86.
17. Langkulsen U, Vichit-Vadakan N, Taptagaporn S. Health impact of climate change on occupational health and productivity in Thailand. Glob Health Action. 2010;3(5607).
18. McMichael AJ, Wilkinson P, Kovats RS, et al. International study of temperature, heat and urban mortality: the 'ISOTHURM' project. Int J Epidemiol. 2008 Oct;37(5):1121-31.
19. Pudpong N, Hajat S. High temperature effects on out-patient visits and hospital admissions in Chiang Mai, Thailand. Sci Total Environ. 2011;409:5260–7.
20. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. Association between occupational heat stress and kidney disease among 37,816 workers in the Thai Cohort Study (TCS). J Epidemiol. 2012;22.
21. Sleigh A, Seubsman S, Bain C. Cohort profile: The Thai Cohort of 87,134 Open University students. Int J Epidemiol. 2008 Apr;37(2):266-72.
22. Grad FP. The Preamble of the Constitution of the World Health Organization. Bull World Health Organ. 2002;80(12):981-4.
23. Cummins RA, Eckersley R, Pallant J, et al. Developing a National Index of Subjective Wellbeing: The Australian Unity Wellbeing Index. Soc Indic Res. 2003;64(2):159-90.
24. Yiengprugsawan V, Seubsman S, Khamman S, et al. Personal wellbeing index in a national cohort of 87,134 Thai adults. Soc Indic Res. 2010;98(2):201-15.
25. StataCorp. Stata 12.0 for Windows. College Station TX: StataCorporation; 2011.
26. Kanazawa M, Yoshiike N, Osaka T, et al. Criteria and classification of obesity in Japan and Asia-Oceania Asia Pac J Clin Nutr. 2002;11:S732-S7.
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27. Hajat S, O'Connor M, Kosatsky T. Health effects of hot weather: from awareness of risk factors to effective health protection. Lancet. 2010;375(9717):856-63.
28. McMichael AJ, Woodruff RE, Hales S. Climate change and human health: present and future risks. Lancet. 2006;367(9513):859-69.
29. Kjellstrom T, Butler AJ, Lucas RM, et al. Public health impact of global heating due to climate change: potential effects on chronic non-communicable diseases. Int J Public Health. 2010;55:97-103.
30. Lan L, Lian Z, Pan L. The effects of air temperature on office workers’ well-being, workload and productivity-evaluated with subjective ratings. Appl Ergon. 2010;42(1):29-36.
31. Anderson C. Heat and violence. Curr Dir Psychol Sci. 2001;10(1):33-8.
32. Nitschke M, Tucker GR, Bi P. Morbidity and mortality during heatwaves in metropolitan Adelaide. Med J Aust. 2007;187(11):662-5.
33. Hansen AL, Bi P, Nitschke M, et al. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect. 2008;116(10):1369 - 75.
34. Anderson C, Anderson K, Dorr N, et al. Temperature and aggression Adv Experimental Social Psychology. 2000;32:63-133.
35. Cheatwood D. The effects of weather on homicide. J Quant Criminol. 1995;11(1):51-70.
36. Maes M, De Meyer F, Thompson P, et al. Synchronized annual rhythms in violent suicide rate, ambient temperature and the light-dark span. Acta Psychiatr Scand. 1994 Nov;90(5):391-6.
37. Bouchama A, Dehbi M, Mohamed G, et al. Prognostic factors in heat wave-related deaths: A meta-analysis. Arch Intern Med. 2007;167(20):2170-6.
38. Guo Y, Punnasiri K, Tong S. Effects of temperature on mortality in Chiang Mai city, Thailand: a time series study. Environ Health. 2012;11(1):36.
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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cross-sectional studies
Section/Topic Item
# Recommendation Reported on page #
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 2
(b) Provide in the abstract an informative and balanced summary of what was done and
what was found
2
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 4
Objectives 3 State specific objectives, including any prespecified hypotheses 5
Methods
Study design 4 Present key elements of study design early in the paper 6
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,
exposure, follow-up, and data collection
6
Participants
6
(a) Give the eligibility criteria, and the sources and methods of selection of participants 6
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect
modifiers. Give diagnostic criteria, if applicable
7
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of assessment
(measurement). Describe comparability of assessment methods if there is more than
one group
7
Bias 9 Describe any efforts to address potential sources of bias 6
Study size 10 Explain how the study size was arrived at 8
Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe
which groupings were chosen and why
7
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 7
(b) Describe any methods used to examine subgroups and interactions 7
(c) Explain how missing data were addressed 8
(d) If applicable, describe analytical methods taking account of sampling strategy -
(e) Describe any sensitivity analyses -
Results
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Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially
eligible, examined for eligibility, confirmed eligible, included in the study, completing
follow-up, and analysed
8
(b) Give reasons for non-participation at each stage -
(c) Consider use of a flow diagram -
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and
information on exposures and potential confounders
8
(b) Indicate number of participants with missing data for each variable of interest -
Outcome data 15* Report numbers of outcome events or summary measures 9
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and
their precision (eg, 95% confidence interval). Make clear which confounders were
adjusted for and why they were included
9
(b) Report category boundaries when continuous variables were categorized -
(c) If relevant, consider translating estimates of relative risk into absolute risk for a
meaningful time period
-
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity
analyses
10
Discussion
Key results 18 Summarise key results with reference to study objectives 10
Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or
imprecision. Discuss both direction and magnitude of any potential bias
13
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,
multiplicity of analyses, results from similar studies, and other relevant evidence
11
Generalisability 21 Discuss the generalisability (external validity) of the study results 12
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if
applicable, for the original study on which the present article is based
18
*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
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Tawatsupa Page 1
Heat stress, health, and wellbeing: findings from a large
national cohort of Thai adults
Benjawan Tawatsupa1, 2,*
, Vasoontara Yiengprugsawan1, Tord Kjellstrom
1, 3,
Sam-ang Seubsman4, Adrian Sleigh1, and the Thai Cohort Study Team
1 National Centre for Epidemiology and Population Health, ANU College of Medicine,
Biology and Environment, the Australian National University, Canberra, Australia
2 Health Impact Assessment Division, Department of Health, Ministry of Public Health,
Nonthaburi, Thailand
3 Centre for Global Health Research, Umeå University, Umeå, Sweden
4 School of Human Ecology, Sukhothai Thammathirat Open University, Nonthaburi, Thailand
*Corresponding author:
Benjawan Tawatsupa,
The Australian National University
Building 62 – NCEPH, Mills Rd, 0200, Canberra, Australia
Email [email protected], [email protected]
Tel: +61 2 6125 5615; Fax: +61 2 6125 0740
The Thai Cohort Study Team
Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn,
Suwanee Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol,
Janya Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai
Somboonsook, Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun,
Wanee Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell,
Bruce Caldwell, Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David
Harley, Matthew Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony
McMichael, Tanya Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara
Yiengprugsawan.
Keywords: Heat stress, health, wellbeing, Thailand Word count: 2,757 words
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Abstract
Objectives: This study aims to examine the association between self-reported heat stress
interference with daily activities (sleeping, work, travel, housework, exercise) and three
graded holistic health and wellbeing outcomes (energy, emotions, life satisfaction).
Design: A cross-sectional study.
Setting: The setting is tropical and developing countries as Thailand, where high temperature
and high humidity are common, particularly during the hottest seasons.
Participants: This study is based on an ongoing national Thai Cohort Study of distance-
learning open-university adult students (N=60,569) established in 2005 to study the health-
risk transition.
Primary and secondary outcome measures: Health impacts from heat stress in our study
are categorized as physical health impacts (energy levels), mental health impacts (emotions),
and wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds
Ratios (ORs) and 95% confidence intervals using multinomial logistic regression adjusting
for a wide array of potential confounders.
Results: Negative health and wellbeing outcomes (low energy level, emotional problems,
and low life satisfaction) associated with increasing frequency of heat stress interfering with
daily activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and
in general worse than energy level (between 1·31 and 2·91), and life satisfaction (between
1·10 and 2·49). The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
Conclusions: In tropical Thailand there already are substantial heat stress impacts on health
and wellbeing. Increasing temperatures from climate change plus the ageing and urbanisation
of the population could significantly worsen the situation. There is a need to improve public
health surveillance and public awareness regarding the risks of heat stress in daily life.
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Article summary
• Article focus:
o To examine the association between self-reported heat stress interference with
daily activities (sleeping, work, travel, housework, exercise) during hot season
and three graded holistic health outcomes (energy, emotions, life satisfaction)
in Thailand.
• Key messages:
o Negative health and wellbeing outcomes (low energy level, emotional
problems, and low life satisfaction) associated with increasing frequency of
heat stress interfering with daily activities.
o The worst health outcomes were when heat interfered with sleeping, followed
by interference with daily travel, work, housework and exercise.
o The results from this study point to the need for improving public health
surveillance and public awareness regarding the risks of heat stress in daily life
in a tropical country like Thailand.
• Strengths and limitations of this study:
o The possible limitation of self-reports, but note that questions on heat stress
and health outcomes were in different parts of the questionnaire.
o The strength of this study is its large scale with participation from a national
group of adults embedded in the socioeconomic mainstream of Thai society
and used the comprehensive questionnaire which captures a detailed
assessment of health and an array of geodemographic, environmental and
social attributes.
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Introduction
Over the last decade interest has grown in the impact of global warming on human health.(1)
Increasing heat stress has substantial adverse effects on population mortality and
morbidity.(2-5) This information is from developed and temperate countries(3) and leaves
unanswered questions for tropical and developing countries where high temperature and
humidity are common. Furthermore, heat stress in tropical cities is increasing due to urban
heat island effects caused by industrial development and urbanisation in developing
countries.(6)
Heat stress can have a major influence on daily human activities. The body absorbs external
heat due to high air temperature and humidity, low air movement, and high solar radiation; as
well, some physical activities generate heat internally.(7) Excess heat exposure during normal
daily activities creates a high risk of recurrent dehydration and can cause other effects on
physical health (eg, exhaustion, heat cramps, heat stroke, or death).(7) Heat stress affects
mood, increases psychological distress and mental health problems,(8-10) and also reduces
key human psychological performance variables.(11)
Other heat stress impacts may arise from increased mistakes in daily activities and accidental
injuries. As well, disturbed sleep and degraded physical performance from heat exhaustion
reduce work capacity and lead to loss of income.(8, 12-13) Populations at risk of heat stress
are not only the elderly but also young people and adults who are more likely to carry out
heavy labour outdoors or work indoors without air conditioning or other effective cooling
systems during the hot season.(8, 12, 14)
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In tropical Thailand, hot and humid conditions are common, especially in the hot season
(March - June). The monthly maximum, mean and minimum temperatures averaged from
1999 to 2008 were around 33°C, 27°C, and 22°C respectively with the averaged relative
humidity at 75%. The monthly maximum temperatures averaged during ten years varied little
by region (32-33°C) and were highest in the North region during April (40°C) and lowest in
the same region during December (24°C).(Tawatsupa et al, unpublished data, 2012)
Global warming (or “global heating” may be a better description in relation to Thailand) is
now causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the
monthly mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean
minimum temperature increased even more at 1·44 ˚C.(15) Heat stress is already a concern in
Thailand and the observed trends indicate further increase in air temperature.(16) A recent
study of occupational heat stress in Thailand by Langkulsen et al(17) revealed a very serious
problem (“extreme caution” or “danger”) in an array of work settings (they tested a pottery
factory, a power plant, a knife manufacture site, a construction site and an agricultural site).
Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities
(18-19) and for workers.(10, 20) However, there is no available information on how much
heat interferes with normal daily activities and heat stress effects on health and well-being in
the general Thai population. Here we report an investigation of association between heat
stress interference with daily activities and health and wellbeing in a large national cohort of
young and middle aged Thai adults.
Methods
Study population
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In 2005, a baseline questionnaire was mailed out to adult students enrolled at Sukhothai
Thammathirat Open University (STOU). The questionnaire was developed by a multi-
disciplinary team in both Thailand and Australia to cover a wide range of topics for a
longitudinal study of the Thai Health-Risk Transition – transformation of the health-risk and
outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge.
Overall, 87,134 distance learning students aged 15 to 87 years responded from all areas of
Thailand. Cohort participants were generally similar to the population of Thailand, especially
in the 30-39 years age group, for sex ratio, income and geographical location.(21)
Data collected included demographic, socioeconomic and geographic characteristics, physical
and mental health status, personal wellbeing, health service use, risk behaviors, injuries, diet,
physical activity, and family background. A four-year follow-up was conducted in 2009 and
the next one is due in 2013.
This report is based on the 2009 follow-up which included questions on heat interference with
normal daily activities. The heat stress and health outcome measures (both described below)
were in different parts of the questionnaire. They could not easily be linked in the respondents
mind so answers on these issues were independent. Covariates analyzed are described with
the results and include age, sex, marital status, geographic location, work status, smoking,
drinking, and Body Mass Index.
Measures of heat stress
Questions related to heat stress were as follows: “How often did the hot period this year
interfere with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work;
and 5) exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times
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per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means heat
stress causing an uncomfortable feeling when doing those daily activities. For analysis, we
grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per month), and ‘often’
(1-6 times per week or every day).
Measures of health and wellbeing outcomes
Health is defined by World Health Organization (WHO) as “a complete state of physical,
mental, and social wellbeing and not merely the absence of disease or infirmity”.(22) Health
impacts from heat stress in our study are categorized as physical health impacts (eg, energy
levels), mental health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three
outcomes were selected because they match the holistic WHO health definition and represent
fundamental health states. Many other more specific diseases would be expected to follow
adverse outcomes for these health measures (see Discussion).
To measure the physical and mental health impacts we used two questions from the standard
Medical Outcomes Short Form Instrument (SF8) as follows: Energy: “During the past four
weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’,
‘a little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the
past four weeks, how much have you been bothered by emotional problems (such as feeling
anxious, depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite
a lot’, and ‘extremely’. For analysis the last two categories were combined. To measure
Wellbeing we used a standardised question:(23-24) “Thinking about your own life and
personal circumstances, how satisfied are you with your life as a whole?” Scores range from 0
(‘completely dissatisfied’) to 10 (‘completely satisfied’).
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Data processing and statistical analysis
Data scanning and editing involved checking the actual questionnaire response against its
digital value using Thai Scandevet, SQL and SPSS software. For analysis we used
multinomial logistic regression reporting odds ratios (adjusted for potential confounders)
based on Stata version 12.(25) For all three fundamental health outcomes (energy, emotions,
wellbeing), the multinomial regression estimates the odds with which each of three
increasingly severe abnormalities occurs relative to the odds of an optimal outcome.
Individuals with missing data were excluded so totals presented vary a little according to
information available.
Ethical considerations
Ethics approval was obtained from Sukhothai Thammathirat Open University Research and
Development Institute (protocol 0522/10) and the Australian National University Human
Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from
all participants.
Results
We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not shown).
The two groups were similar for age, sex ratio, employment, income, and health outcomes
studied here (energy levels, emotional problems, life satisfaction). Socio-demographic and
health characteristics of the 60,569 cohort members followed up in 2009 are presented in
Table 1. There were slightly more females (54·8%), 70% were aged less than 40 years, and
55·3% were married. Nearly 20% reported household monthly income of less than 10,000
Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban areas.
Health risk behaviors - regular smoking or regular alcohol drinking -were reported by 7·7%
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and 13·7%, respectively. By Asian standards,(26) half the cohort members were in the normal
weight range, 9·5% were underweight, 18·8% were overweight, and 22·1% were obese.
We noted that prevalence of ‘often’ heat interference for each daily activity are not much
different in different regions of Thailand (33-42% for daily travel, 29-38% for work, 26-32%
for housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat
interference frequency categories are summarized in Table 2. Heat interference ‘often’ was
reported (in order of frequency) by 37·5% for daily travel, 34·5% for work, 29·9% for
housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing frequency
outcomes are reported in Table 3: 37·6% reported being very satisfied with their life, around
15% reported having very much energy in the past 4 weeks and close to 11% reported no
emotional problems in the past 4 weeks.
Daily activities show a clear trend connecting increasing heat interference with worse health
and wellbeing (Table 4). For example, cohort members who experienced heat interference
‘often’ while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently
than ‘no’ emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was
found for those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the
same trend was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have
also shown strong gradients connecting frequent heat interference and worse health outcomes.
The multinomial logistic regression, adjusting for a wide array of potential confounders (see
footnote for Table 5), supported the descriptive results. For all three health outcomes, when
each of the three graded adverse outcome categories is compared to the optimal outcome, the
relative odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for
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each health outcome, more heat interference associates more strongly with a given grade of
abnormality). And 95% confidence intervals for all odds ratios indicated statistical
significance. So heat stress interfering with normal daily activities (sleep, housework, travel,
work, exercise) associates with adverse outcomes for all three holistic measures of health. For
example, reporting heat interference ‘often’ while sleeping was strongly associated with ‘little
or none’ energy [OR = 2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81,
95% CI 4·32-5·36] and ‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work,
reporting heat interference ‘often’ was associated with ‘little or none’ energy [OR = 2·45,
95% CI 2·22-2·71] and ‘extreme’ emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar
results were found during daily travel and doing housework. A statistically significant
association was also found for heat inference during exercise but the magnitude of the effect
was lower than for other activities.
Discussion
Our study shows that climate-related heat stress in tropical Thailand associated with self-
reported health and wellbeing if the heat interfered with daily activities such as sleep,
housework, travel, work, and exercise. The large study group included young and middle-age
Thai adults, mostly doing paid work, with a little over half residing in urban areas. These
cohort members are active and over 20% report often experiencing heat interference for daily
activities during the hot season. Daily travel and work were sources of heat stress more often
than other activities, probably because they involve time spent in traffic or outdoors during
hot periods. Other activities such as housework have less heat stress than daily travel and
work, perhaps because these activities are home-based where air-conditioning or other
ventilation is available.
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We found those who report higher levels of heat stress interference with daily activities tend
to also be the ones who have adverse health and wellbeing outcomes (low life satisfaction,
low energy level, and worse emotional problems). Odds Ratios of heat stress effects across all
daily activities for emotional problems are between 1·55 and 4·81 and in general are worse
than energy level effects (between 1·31 and 2·91) and life satisfaction effects (between 1·10
and 2·49). The worst health outcomes were for heat stress while sleeping followed by heat
stress for daily travel, work, housework and exercise.
Our data are based on self-report by educated Thais and we note that questions on heat stress
and health outcomes were in different parts of the questionnaire. Findings show strong and
highly consistent trends especially for adverse health effects of frequent heat interference
during sleep, daily travel, and work. Elsewhere we have completed detailed analyses of
associations between heat stress and self-reported health outcomes in the cohort using the
questions from SF8 (10). Our studied outcomes in this report were holistic fundamental
measures of health. We can expect that those who had abnormal findings would also (already
or eventually) manifest other more specific chronic diseases such as depression, obesity,
hypertension, and kidney disease. If so, the eventual burden of heat-related disease will be
higher than currently recognized.(27-29)
Our findings add to some previous reports on working in hot environments which found that
heat stress significantly reduced people’s motivation to do their work. Lan et al (30) assessed
office workers’ perceptions of thermal environment, emotions, well-being, and motivation to
work, and found that participants had lower motivation to work and experienced more
negative moods in hot environments. Anderson found that the prolonged, continuous
repetitive actions required to maintain performance at work and achieve target goals (such as
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getting a job finished) can lead to hypertension.(31) And when more effort was required to
complete a task in hot conditions loss of motivation was experienced leading to lower
productivity and increased injury risk. The impact of heat stress on psychological
performance variables (11) is a likely factor in these work related impacts of heat.
Psychological effects of heat stress have been noted in other settings as well. Nitschke et al
(32) reported a positive association between high ambient temperature and hospital
admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses for
which admissions increased included anxiety, symptomatic mood disorders, and
psychological development disorders among elderly people when temperature exceeded
26·7°C.(33) Moreover, excessive heat stress exposure may also increase violence.(31-34)
Increasing heat stress had been associated with higher rates of aggressive behavior,(35) and
higher violent suicide rates.(36) In a meta-analysis, Bouchama et al (37) concluded that pre-
existing mental health problems tripled the risk of all-cause mortality during a heat wave. A
related issue is the physical and psychological exhaustion caused by extreme heat stress. (7)
In our study, we found that heat stress in Thailand is not only a problem at work but also heat
stress interferes with other daily activities including sleeping, daily travel, housework and
exercise. The results of our study complement other Thai research about adverse effects of
heat. One recent report shows that heat stress in Thailand is a very serious problem in a wide
variety of work settings (17). McMichael et al (18) and Guo et al (38) found a temperature–
mortality association and Pudpong et al (19) found heat related excess hospital admissions.
Worker studies in Thailand related occupational heat stress, kidney disease and psychological
distress.(10, 20)
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One limitation of this study is that it could not directly establish that health and wellbeing
outcomes arose as a result of heat stress. Interpreting causality between heat stress exposure
and health and wellbeing outcomes is complex in a cross-sectional study as we cannot be
completely sure that heat stress preceded their health condition and wellbeing. Also, the
source of the heat stress was not reported and we could not make direct measurements of heat
stress exposure and health and wellbeing outcomes. Another limitation of this study arose
because people answered the questionnaire at different times of the year (but most in March to
July - the hot period). The questions on physical and emotional health assessed the previous
four weeks so most (almost all) were answering for the hot period.
The strength of this study is its large scale with participation from a national group of adults
embedded in the socioeconomic mainstream of Thai society. Other strengths include the
comprehensive questionnaire which captures a detailed assessment of health and an array of
geodemographic, environmental and social attributes. Also, the cohort has been set up for
future longitudinal analysis which will provide better insight into causal pathways between
heat stress and subsequent health outcomes in the long run.
We conclude that Thai populations are at high risk of heat stress during daily activities. Also,
in Thailand an anticipated increase in temperature from climate change plus the ageing and
urbanisation of the population could significantly increase heat impacts on health and
wellbeing. There is a need for improvements in public health surveillance and public
awareness regarding the risks of heat stress which hitherto have been considered
unremarkable in such a tropical environment.
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Tables
Table 1 Socio-demographic and health characteristics of Thai cohort members in 2009
Cohort characteristics N = 60,569 %
Demographic characteristics
Sex Male 45.3
Female 54.8
Age (year) ≤ 29 27.4
30-39 42.6
40+ 30.0
Marital status Married 55.3
Never married 37.9
Separated, divorced, widowed 6.8
Socio-geographic characteristics
Monthly income (Baht)* ≤10,000 18.8
10,001-20,000 22.4
20,001-30,000 35.7
>30,000 23.1
Work status Doing paid work 73.2
Unpaid family workers 7.3
Seeking work 2.2
Others 17.3
Residence Rural residence 44.0
Urban residence 56.0
Health risk behaviors
Regular smokers 7.7
Regular alcohol drinkers 13.7
Body Mass Index (kg/m2)
Underweight (<18.5) 9.5
Normal (18.5-22.9) 49.5
Overweight at risk (23-24.9) 18.8
Obese (25+) 22.1
*Household monthly income in 2009 (US$ = 35 Baht)
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Table 2 Daily activities and heat interference category among Thai cohort members in 2009
Daily activities
N = 60,569
Heat interference (%)
Not applicable* Never Sometimes Often
Sleeping 15.7 24.3 32.5 27.4
Housework 1.3 37.1 31.7 29.9
Daily travel 3.0 33.7 25.8 37.5
Work 14.0 30.3 21.2 34.5
Exercise 0.8 43.1 30.1 25.9
*Use air conditioner
Table 3 Health and wellbeing outcomes among Thai cohort members in 2009
Outcomes
N = 60,569
%
Overall life satisfaction (score ranged from 0 to 10)
9-10 very satisfied (highest) 37.6
8 (high) 28.8
6-7 (medium) 21.7
0-5 not very satisfied (low) 12.0
Energy level in the past 4 weeks
very much 14.9
quite a lot 44.0
some 32.0
a little or none 9.1
Emotional problems in the past 4 weeks
not at all 11.3
slightly 48.4
moderately 25.8
quite a lot/extremely 14.5
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Table 4 Frequency of heat interference with daily activities by health & wellbeing outcomes among cohort members
Daily activities and
heat interference
category
Health and wellbeing outcomes N=60,569
% Life satisfaction
score ranged from 0 to 10
% Energy level
in the past 4 weeks
% Emotional problems
in the past 4 weeks
9-10
highest
8
high
6-7
medium
0-5
low
very much quite a lot some
little/ none not at all slightly
moderate
extreme
Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)
never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6
sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3
often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9
Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)
never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7
sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4
often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9
Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)
never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2
sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4
often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0
Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)
never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6
sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9
often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7
Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)
never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2
sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9
often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2
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Table 5 Association between heat interference with daily activities and health & wellbeing outcomes among cohort members
Heat
interference
category
N=60,569
Adjusted* Odds Ratios and 95% Confidence Interval
Life satisfaction (score 0-10)** Energy level in the past 4 weeks Emotional problems in the past 4 weeks
high
vs
highest
medium
vs
highest
low
vs
highest
quite a lot
vs
very much
some
vs
very much
little/none
vs
very much
slightly
vs
not at all
moderate
vs
not at all
extreme
vs
not at all
Sleep
never ref ref ref ref ref ref ref ref ref
sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]
often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]
Housework
never ref ref ref ref ref ref ref ref ref
sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]
often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]
Daily travel
never ref ref ref ref ref ref ref ref ref
sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]
often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]
Work
never ref ref ref ref ref ref ref ref ref
sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]
often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]
Exercise
never ref ref ref ref ref ref ref ref ref
sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]
often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]
*Multivariate regression adjusting for potential confounders: age, sex, marital status, work status, household income, urban-rural residence, exercise, housework, hours of
sleep, body mass index, smoking , and drinking
**Life satisfaction scores: highest = 9-10, high = 8, medium = 6-7, low = 0-5
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Acknowledgments
This study was supported by the International Collaborative Research Grants Scheme with
joint grants from the Wellcome Trust UK (GR071587MA) and the Australian National Health
and Medical Research Council (NHMRC 268055), and as a global health grant from the
NHMRC (585426). These funding bodies play no role in the preparation or submission of this
manuscript. We thank the staff at Sukhothai Thammathirat Open University (STOU) who
assisted with student contact, and the STOU students who are participating in the cohort
study. We also thank Dr Bandit Thinkamrop and his team from Khon Kaen University for
guiding us successfully through the complex data processing.
Competing interests
We declare that we have non-financial competing interests.
Contributor statement
The corresponding author had full access to all data used in the study and had final
responsibility for the decision to submit for publication. BT and VY conceptualized the
analysis for this paper with contributions from all authors. BT and VY wrote the first draft.
BT did the literature search and VY did statistical analyses. TK had the initial idea for the
heat stress study. SS and AS conceived and executed the Thai Cohort Study and assisted with
the writing and interpretation. All authors contributed to and approved the final version.
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Reference lists
1. Confalonieri U, Menne B, Akhtar R, Ebi K, Hauengue M, Kovats RS, et al. Human Health. Climate change 2007: Impacts, adaptation and vulnerability, contribution of working group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press; 2007 [cited 2012 13 March]; Available from: http://www.ipcc-wg2.org
2. Basu R, Samet JM. Relation between elevated ambient temperature and mortality: A review of the epidemiologic evidence. Epidemiol Rev. 2002;24(2):190-202.
3. Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41-55.
4. Basu R. High ambient temperature and mortality: A review of epidemiologic studies from 2001 to 2008. Environ Health. 2009;8(40).
5. Bi P, Williams S, Loughnan M, Lloyd G, Hansen AL, Kjellstrom T, et al. The effects of extreme heat on human mortality and morbidity in Australia: Implications for public health. Asia Pac J Public Health. 2011;23(2 Suppl):27S-36S.
6. Campbell-Lendrum D, Corvalan C. Climate change and developing-country cities: implications for environmental health and equity. J Urban Health. 2007;84(1 Suppl):i109-17.
7. Parsons K. Human thermal environments: the effects of hot, moderate, and cold environments on human health, comfort and performance. 2nd ed. London: Taylor & Francis; 2003.
8. Kjellstrom T. Climate change, direct heat exposure, health and well-being in low and middle-income countries. Glob Health Action. 2009;2:1-3.
9. Berry HL, Bowen K, Kjellstrom T. Climate change and mental health: a causal pathways framework. Int J Public Health. 2010;55(2):123-32.
10. Tawatsupa B, Lim LL-Y, Kjellstrom T, Seubsman S, Sleigh A, the Thai Cohort Study team. The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers. Glob Health Action. 2010;3(5034).
11. Hancock PA, Ross JM, Szalma JL. A meta-analysis of performance response under thermal stressors. Hum Factors. 2007;49(5):851-77.
12. Kjellstrom T. Climate change exposures, chronic disease and mental health in urban populations:a threat to health security, particularly for the poor and disadvantaged. Kobe, Japan: World Health Organization Centre for Health and Development; 2009.
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13. Kjellstrom T, Holmer I, Lemke B. Workplace heat stress, health and productivity - an increasing challenge for low and middle-income countries during climate change. Glob Health Action. 2009;2.
14. Kjellstrom T, Gabrysch S, Lemke B, Dear K. The "Hothaps" program for assessing climate change impacts on occupational health and productivity: an invitation to carry out field studies Glob Health Action. 2009;2.
15. Limsakul A, Goes JI. Empirical evidence for interannual and longer period variability in Thailand surface air temperatures. Atmos Res. 2008;87(2):89-102.
16. Thai Meteorological Department. Climate change in Thailand for last 52 years. Bangkok: Meteorological Department, Thailand; 2007 [4 February 2012]; Available from: http://www.tmd.go.th/info/info.php?FileID=86.
17. Langkulsen U, Vichit-Vadakan N, Taptagaporn S. Health impact of climate change on occupational health and productivity in Thailand. Glob Health Action. 2010;3(5607).
18. McMichael AJ, Wilkinson P, Kovats RS, Pattenden S, Hajat S, Armstrong B, et al. International study of temperature, heat and urban mortality: the 'ISOTHURM' project. Int J Epidemiol. 2008 Oct;37(5):1121-31.
19. Pudpong N, Hajat S. High temperature effects on out-patient visits and hospital admissions in Chiang Mai, Thailand. Sci Total Environ. 2011;409:5260–7.
20. Tawatsupa B, Lim LL-Y, Kjellstrom T, Seubsman S, Sleigh A, the Thai Cohort Study team. Association between occupational heat stress and kidney disease among 37,816 workers in the Thai Cohort Study (TCS). J Epidemiol. 2012;22.
21. Sleigh A, Seubsman S, Bain C. Cohort profile: The Thai Cohort of 87,134 Open University students. Int J Epidemiol. 2008 Apr;37(2):266-72.
22. Grad FP. The Preamble of the Constitution of the World Health Organization. Bull World Health Organ. 2002;80(12):981-4.
23. Cummins RA, Eckersley R, Pallant J, van Vugt J, Misajon R. Developing a National Index of Subjective Wellbeing: The Australian Unity Wellbeing Index. Soc Indic Res. 2003;64(2):159-90.
24. Yiengprugsawan V, Seubsman S, Khamman S, Lim LL-Y, Sleigh A, the Thai Cohort Study Team. Personal wellbeing index in a national cohort of 87,134 Thai adults. Soc Indic Res. 2010;98(2):201-15.
25. StataCorp. Stata 12.0 for Windows. College Station TX: StataCorporation; 2011.
Page 43 of 44
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26. Kanazawa M, Yoshiike N, Osaka T, Numba Y, Zimmet P, Inoue S. Criteria and classification of obesity in Japan and Asia-Oceania Asia Pac J Clin Nutr. 2002;11:S732-S7.
27. Hajat S, O'Connor M, Kosatsky T. Health effects of hot weather: from awareness of risk factors to effective health protection. Lancet. 2010;375(9717):856-63.
28. McMichael AJ, Woodruff RE, Hales S. Climate change and human health: present and future risks. Lancet. 2006;367(9513):859-69.
29. Kjellstrom T, Butler AJ, Lucas RM, Bonita R. Public health impact of global heating due to climate change: potential effects on chronic non-communicable diseases. Int J Public Health. 2010;55:97-103.
30. Lan L, Lian Z, Pan L. The effects of air temperature on office workers’ well-being, workload and productivity-evaluated with subjective ratings. Appl Ergon. 2010;42(1):29-36.
31. Anderson C. Heat and violence. Curr Dir Psychol Sci. 2001;10(1):33-8.
32. Nitschke M, Tucker GR, Bi P. Morbidity and mortality during heatwaves in metropolitan Adelaide. Med J Aust. 2007;187(11):662-5.
33. Hansen AL, Bi P, Nitschke M, Ryan P, Pisaniello D, Tucker G. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect. 2008;116(10):1369 - 75.
34. Anderson C, Anderson K, Dorr N, DeNeve K, Flanagan M. Temperature and aggression Adv Experimental Social Psychology. 2000;32:63-133.
35. Cheatwood D. The effects of weather on homicide. J Quant Criminol. 1995;11(1):51-70.
36. Maes M, De Meyer F, Thompson P, Peeters D, Cosyns P. Synchronized annual rhythms in violent suicide rate, ambient temperature and the light-dark span. Acta Psychiatr Scand. 1994 Nov;90(5):391-6.
37. Bouchama A, Dehbi M, Mohamed G, Matthies F, Shoukri M, Menne B. Prognostic factors in heat wave-related deaths: A meta-analysis. Arch Intern Med. 2007;167(20):2170-6.
38. Guo Y, Punnasiri K, Tong S. Effects of temperature on mortality in Chiang Mai city, Thailand: a time series study. Environ Health. 2012;11(1):36.
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