SOCIO-ECONOMIC STATUS AND MORTALITY FROM CARDIOVASCULAR DISEASE AMONG PEOPLE WITH TYPE 2

DIABETES IN SCOTLAND (2001-2007)

Caroline Jackson, Jeremy Walker,

Colin Fischbacher, Sarah Wild

on behalf of the Scottish Diabetes Research Network Epidemiology Group

Background

• Incidence and prevalence of type 2 diabetes higher in deprived than affluent communities

• Deprivation has a more marked effect on diabetes prevalence among women than men

• Diabetes associated with increased cardiovascular disease mortality but information on contemporary relative risks limited

• Not clear whether deprivation might confound relationship between diabetes and mortality

Data sources• Scottish Care Initiative – Diabetes Collaboration (SCI-DC) is a

national, population-based electronic register of people with diabetes – includes approx. 95% of people with diagnosed diabetes

• Study based on people registered on SCI-DC who were alive and > 40 years of age at some point during 2001-7

• SCI-DC data linked to national mortality records

• SES represented by Scottish Index of Multiple Deprivation (SIMD) – an area-based measure

• Numbers of people / deaths in Scottish population (by age / sex / calendar year / SIMD quintile ) obtained from General Register Office for Scotland (GROS, now NRS) data

Age-standardised* prevalence of T2DM among 35-84 year olds in

Scotland by SES , 2007RR for most vs least deprived:

1.58 (1.20-2.07) for men

2.00 (1.52 to 2.62) for women

* Using European standard population

SIMD quintile (1 = least deprived)

Ag

e st

and

ard

ised

pre

vale

nce

(%

)

2

4

6

8

1 2 3 4 5

Female Male

Methods

• Non-diabetic population identified by removing the numbers of people with type 2 diabetes at the mid-point of each year from the numbers of people in the whole Scottish population

• European Standard Population used to estimate age-standardised mortality by sex, SIMD quintile and duration of diabetes

• Negative binomial regression used to estimate relative risks of type 2 diabetes for ischaemic heart disease and cerebrovascular disease mortality adjusting for age and stratifying by sex and SIMD quintile

Results

• Data available for 216,172 people with type 2 diabetes who were aged 40+ years during 2001-2007

• 10,576 IHD deaths and 4,377 cerebrovascular deaths among people with T2DM during a total of 979,564 person years of follow-up

Age-standardised ischaemic heart disease mortality rates by socioeconomic status, for

men and women with and without T2DM

Age-

stan

dard

ised

IHD

mor

talit

y ra

te

(per

100

0 pe

rson

yea

rs)

Women

012345678910

1 2 3 4 5

Population with T2DM Population without T2DM

Men

0123456789

10

1 2 3 4 5

Age-standardised IHD

mortality rate

(per 1000 person years)

SIMD quintile (1 = least deprived)

Age-standardised cerebrovascular disease mortality rates by socioeconomic status, for

men and women with and without T2DM

Men

00.5

11.5

22.5

33.5

44.5

5

1 2 3 4 5

Women

00.511.522.533.544.55

1 2 3 4 5

Population with T2DM Population without T2DM

Age-

stan

dard

ised

cer

ebro

vasc

ular

dis

ease

mor

talit

y ra

te (p

er 1

000

pers

on y

ears

)Age-standardised cerebrovascular disease

mortality rate (per 1000 person years)

SIMD quintile (1 = least deprived)

Risk ratios for ischaemic heart disease and cerebrovascular disease mortality, by SES and sex, comparing people with and without T2DM

Ischaemic heart disease mortality

SIMD quintile

1 (least deprived)2

3

45 (most deprived)

SIMD quintile

1 (least deprived)2

3

45 (most deprived)

RR (95% CI)1.95 (1.72 to 2.20)1.84 (1.63 to 2.06)

1.72 (1.54 to 1.92)

1.56 (1.39 to 1.74)1.39 (1.25 to 1.55)

RR (95% CI)2.70 (2.27 to 3.21)2.40 (1.04 to 2.82)

2.16 (1.85 to 2.53)

2.01 (1.72 to 2.35)1.90 (1.64 to 2.21)

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Risk ratios for ischaemic heart disease and cerebrovascular disease mortality, by SES and sex, comparing people with and without T2DM

Ischaemic heart disease mortality

Cerebrovascular disease mortality

SIMD quintile 1 (least deprived)2

3

45 (most deprived)

SIMD quintile

1 (least deprived)2

3

45 (most deprived)

SIMD quintile 1 (least deprived)2

3

45 (most deprived)

SIMD quintile

1 (least deprived)2

3

45 (most deprived)

RR (95% CI)1.95 (1.72 to 2.20)1.84 (1.63 to 2.06)

1.72 (1.54 to 1.92)

1.56 (1.39 to 1.74)1.39 (1.25 to 1.55)

RR (95% CI)2.70 (2.27 to 3.21)2.40 (1.04 to 2.82)

2.16 (1.85 to 2.53)

2.01 (1.72 to 2.35)1.90 (1.64 to 2.21)

RR (95% CI)1.39 (1.16 to 1.68)1.45 (1.23 to 1.72)

1.11 (0.93 to 1.31)

1.19 (1.01 to 1.41)1.05 (0.89 to 1.24)

RR (95% CI)1.64 (1.35 to 2.00)1.43 (1.19 to 1.71)

1.36 (1.14 to 1.63)

1.18 (0.98 to 1.40)1.06 (0.89 to 1.27)

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Mortality greater in populationwith diabetes

Mortality lower in population with diabetes

Discussion

• Marked gradients in diabetes prevalence and cardiovascular mortality by SES

• Absolute mortality higher in people with diabetes than people without diabetes and in deprived compared to affluent populations

• Relative risks higher for women than men and affluent than deprived populations

Possible explanations for differences in RR

• Prevalence of risk factors for diabetes and cardiovascular disease (including previous history of cardiovascular disease) differ by sex and SES

• Higher proportion of undiagnosed diabetes in deprived populations

Summary

• Strengths: large population-based register with almost complete data. Validation of type of diabetes

• Weaknesses: area based measure of SES. Possible misclassification of cause of death. Incompleteness of SCI-DC in early years.

• Further work required to investigate whether differences in risk factor patterns and use of effective treatments explain the effects of socio-economic status on relative risks of type 2 diabetes on cardiovascular mortality and to establish effective interventions to reduce inequalities in health

Acknowledgements

SCI-DC data are available for analysis by members of the Scottish Diabetes Research Network epidemiology group thanks to the hard work of numerous NHS staff who enter the data and people and organisations (the Scottish Care Information – Diabetes Collaboration [SCI-DC] Steering Group, the Scottish Diabetes Group, the Scottish Diabetes Survey Group, the managed clinical network managers and staff in each Health Board) involved in setting up, maintaining and overseeing the SCI-DC system. We thank Cath Storey for her work on data linkage.

This work was supported by the Wellcome Trust through the Scottish Health Informatics Programme (SHIP) Grant (Ref WT086113).

SHIP is a collaboration between the Universities of Aberdeen, Dundee, Edinburgh, Glasgow and St Andrews and the Information Services Division of NHS Scotland. Additional funding for diabetes register linkage was provided by the Scottish Government.

Caroline Jackson is funded by the CSO and MRC.