Copyright by Silvia Esquivel Muñoz 2013
Transcript of Copyright by Silvia Esquivel Muñoz 2013
Copyright
by
Silvia Esquivel Muñoz
2013
The Dissertation Committee for Silvia Esquivel Muñoz certifies that this is the
approved version of the following dissertation:
PSYCHOSOCIAL INFLUENCES OF
ACCULTURATION AND ACCULTURATIVE STRESS ON
LEPTIN, ADIPONECTIN, AND GESTATIONAL DIABETES IN MEXICAN AMERICAN
WOMEN DURING PREGNANCY
Committee: ____________________________________ Eileen K. Kintner, Supervisor ____________________________________ Heather Becker ____________________________________ Alexandra Garcia ____________________________________ Diane Tyler ____________________________________ R. Jeanne Ruiz
PSYCHOSOCIAL INFLUENCES OF ACCULTURATION AND ACCULTURATIVE
STRESS ON
LEPTIN, ADIPONECTIN, AND GESTATIONAL DIABETES IN MEXICAN AMERICAN
WOMEN DURING PREGNANCY
by
Silvia Esquivel Muñoz, BSN, MSN
Dissertation
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy
The University of Texas at Austin
December 2013
Dedication
I would like to dedicate this dissertation to the most self-less and caring individual I have
had the privilege to have in my life, Don Juan Esquivel, for embodying the true
meaning of unconditional love and respect. Everything I have accomplished has been
because of his selfless acts and support. He will never be forgotten and will always be
admired.
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Acknowledgments
I would like to express my full gratitude to everyone who made this possible.
Ernesto Muñoz, for giving me his full support, patience and always believing in me.
My mother Margarita Esquivel and all my family for reminding me Que, Si Se Puede.
Dr. Jeanne Ruiz, for awakening my curiosity, nurturing my imagination, guiding me
through the scientific process, making me believe that the possibilities are endless,
sharing her data, and making this study possible.
Dr. Eileen Kintner, for directing my thought process, always keeping me on task,
reminding me to think like a scientist, and nurturing my confidence.
Dr. Heather Becker, Dr. Alexandra Garcia, Dr. Diane Tyler, for participating in the
dissertation committee, reading the chapters, offering guidance, and support.
The University of Texas at Austin School of Nursing Doctoral Program Faculty, for
fostering scientific learning, teaching future scientists, promoting research, and nursing
science.
Dr. Julie Zuñiga, my good friend who shared her own experiences with the doctoral
program and gave me insight on what was coming ahead.
S. Maggie McCray, my colleague and friend who sat next to me at work and listened to
every school story, listened without judgment, and reminded me it was all possible.
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PSYCHOSOCIAL INFLUENCES OF
ACCULTURATION AND ACCULTURATIVE STRESS ON
LEPTIN, ADIPONECTIN, AND GESTATIONAL DIABETES IN MEXICAN AMERICAN
WOMEN DURING PREGNANCY
Silvia Esquivel Muñoz Ph. D
The University of Texas at Austin, 2013
Supervisor: Eileen Kintner
The purpose of this biobehavioral study was to explore relationships between
psychosocial stressors of acculturation, acculturative stress, and metabolic markers of
leptin and adiponectin in Mexican American women with and without GDM. A case
control design was used for this secondary analysis which included a sample of 38
pregnant women with GDM and 38 healthy controls without GDM, who were matched on
age and BMI status. Subjects completed two surveys—the Multidimensional
Acculturation Scale II (MASII) and the Multidimensional Acculturative Stress Inventory
(MASI)—which measured acculturation and acculturative stress. Descriptive statistics,
Pearson r correlations, and independent sample t-tests were used to analyze the data.
The results from this study indicated that significant relationships do exist between some
of the variables of interest; however, there were no overall significant differences found
between women with and without gestational diabetes. These mixed results may be an
indicator of a need to further explore these concepts.
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TABLE OF CONTENTS
ABSTRACT ............................................................................................................................. vi LIST OF TABLES .................................................................................................................... x LIST OF FIGURES .................................................................................................................. xi CHAPTER I. INTRODUCTION ................................................................................................ 1
Diabetes ............................................................................................................................ 1 Altered Glucose Metabolism .............................................................................................. 3 Purpose ............................................................................................................................. 6 Significance to Nursing ...................................................................................................... 7 Assumptions ...................................................................................................................... 7 Conceptual Framework ..................................................................................................... 8 Concepts ........................................................................................................................... 12
Gestational Diabetes Mellitus .................................................................................... 12 Psychosocial Stress .................................................................................................. 13
Acculturation .................................................................................................... 14 Acculturative Stress ......................................................................................... 14
Metabolic Responses ................................................................................................ 15 Leptin ............................................................................................................... 15 Adiponectin ...................................................................................................... 16
Research Questions .......................................................................................................... 16 Summary ........................................................................................................................... 17
CHAPTER II. REVIEW OF THE LITERATURE ....................................................................... 19
Hypothalamic-Pituitary-Adrenal Axis .................................................................................. 19 Psychosocial Stress .......................................................................................................... 20 Stress in Mexican American Women ................................................................................. 25
Acculturation ............................................................................................................. 25 Acculturative Stress .................................................................................................. 27
Metabolic Response to Stress ........................................................................................... 29 Leptin ........................................................................................................................ 36 Adiponectin ............................................................................................................... 38
Gestational Diabetes ......................................................................................................... 40 Summary ........................................................................................................................... 41
CHAPTER III. METHODS ...................................................................................................... 43
Institutional Review Board Approval .................................................................................. 43 Research Design ............................................................................................................... 43
Sampling Procedures ................................................................................................ 44 Case-control Sample ................................................................................................ 45 Recruitment of Subjects for the Parent Study ........................................................... 46 Securing Informed Consent ...................................................................................... 46
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Ethical Considerations ....................................................................................................... 47 Protecting human rights of subjects ......................................................................... 47 Balancing benefits and risks of a study .................................................................... 48
Measures .......................................................................................................................... 48
Multidimensional Acculturative Stress Inventory (MASI) .......................................... 49 Multidimensional Acculturation Scale II (MAS II) ...................................................... 49 Leptin ........................................................................................................................ 51 Adiponectin ............................................................................................................... 52
Data Collection Procedures .............................................................................................. 52 Survey Data .............................................................................................................. 52 Physiologic Data ....................................................................................................... 52
Data Analysis ................................................................................................................... 53 Physiologic Data ....................................................................................................... 53
Threats to Design Validity ................................................................................................. 55 Statistical Validity ..................................................................................................... 55 Internal Validity ........................................................................................................ 55 Construct Validity ..................................................................................................... 56 External Validity ....................................................................................................... 56
Summary .......................................................................................................................... 56 CHAPTER IV. RESULTS ........................................................................................................ 57
Description of Sample ...................................................................................................... 57 Demographic Statistics ............................................................................................. 57
Gestational Diabetes Group ............................................................................. 57 Healthy Control Group (Non-Gestational Diabetes) .......................................... 58
Biologic Characteristics ............................................................................................. 60 Measures .................................................................................................................. 62
Multidimensional Acculturation Scale (MAS II) ................................................. 62 Multidimensional Acculturative Stress (MASI) .................................................. 62 Leptin ............................................................................................................... 64 Adiponectin ...................................................................................................... 64
Research Questions ......................................................................................................... 65 Research Question 1 ................................................................................................ 65 Research Question 2.1 ............................................................................................. 73 Research Question 2.2 ............................................................................................. 73
Summary ........................................................................................................................... 75
CHAPTER V. DISCUSSION AND SUMMARY ...................................................................... 76
Interpretation of Findings .................................................................................................. 76 Psychosocial Stress .................................................................................................. 76 Metabolic Response ................................................................................................. 78 Gestational Diabetes................................................................................................. 80
Limitations ........................................................................................................................ 81 Self-Report Measures ............................................................................................... 81
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Sample Size ............................................................................................................ 81 Matching Techniques ................................................................................................ 82
Application to the Development of Nursing Theory ........................................................... 82 Implications for Nursing Practice ...................................................................................... 83 Recommendations for Future Research ........................................................................... 85 Summary .......................................................................................................................... 86
APPENDIX A .......................................................................................................................... 88 APPENDIX B .......................................................................................................................... 97 REFERENCES ........................................................................................................................ 98
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LIST OF TABLES
TABLE 1.1 Definitions of Concepts Contained in the Psychosocial Stress and
Metabolic Response in Gestational Diabetes Mellitus Model ..............................10 TABLE 2.1 Summary of Studies on Acculturation and Acculturative Stress in Mexican
Americans ..............................................................................................................22
TABLE 2.2 Summary of Studies Investigating Leptin and Adiponectin in Gestational
Diabetes.................................................................................................................31
TABLE 4.1 Demographic Characteristics of Women with and without Gestational
Diabetes.................................................................................................................59
TABLE 4.2 Biologic Characteristics of Women with and without Gestational Diabetes
...............................................................................................................................61
TABLE 4.3 MASII and MASI Subscale Survey Scores ...........................................................63
TABLE 4.4a Correlations among Study Variables ....................................................................71
TABLE 4.4b Correlations among Study Variables ....................................................................72
TABLE 4.5 Independent t-test Analysis of Difference between Women with and
Without Gestational Diabetes................................................................................74
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LIST OF FIGURES
FIGURE 1.1 Psychosocial Stress and Metabolic Response in Gestational Diabetes
Model .....................................................................................................................11
1
CHAPTER I
INTRODUCTION
This chapter addresses the need for this research by describing the health
problem and summarizing the impact of altered glucose metabolism. The purpose of the
study and its significance for nursing are presented. Assumptions are delineated and the
conceptual framework is specified. Next, concepts are defined and hypotheses are
presented for relationships among the concepts. Finally, the research questions are
posed.
Diabetes
Diabetes is a metabolic disease characterized by hyperglycemia resulting from
defects in insulin secretion, insulin action, or both (American Diabetes Association
[ADA], 2011), and is the seventh leading cause of death in United States (Centers for
Disease Control and Prevention [CDC], 2011). Type 2 diabetes (T2DM) accounts for
between 90% and 95% of those with diabetes, and encompasses individuals who have
both insulin resistance and relative insulin deficiency (ADA, 2011). Alterations in glucose
metabolism lead to high levels of glucose in the blood, which places the body at risk for
altered processes that can cause complications of T2DM including cardiovascular
disease, renal and neurological diseases, blindness, and lower limb amputations (CDC,
2011). Some of the major risk factors for T2DM include obesity, Hispanic ethnicity, and
history of Gestational Diabetes Mellitus (GDM).
GDM is any degree of glucose intolerance with onset or first recognition during
pregnancy (ADA, 2011). GDM consists of a combination of insulin resistance and beta
cell dysfunction that leads to altered carbohydrate metabolism (Retnakaran et al., 2003).
Approximately 7% of all pregnancies are complicated by GDM, resulting in more than
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200,000 cases annually (ADA, 2011; CDC 2011). It is estimated that between 35% and
60% of women who had GDM will develop T2DM within 10 to 20 years of the pregnancy
(ADA, 2011; CDC. 2011). The combination of the risk factors of high prevalence of
obesity and Hispanic ethnicity places Mexican American women with a history of GDM
at very high risk for later development of T2DM.
Diabetes is more common in Hispanics, affecting 11.8% of this population
compared to 7.1% of non-Hispanic White Americans (CDC, 2011). Prevalence of
diabetes among Mexican Americans has reported to be even greater—14% (CDC,
2011). Hispanic Americans also are at increased risk for diabetes complications due to
increased poverty and lack of health insurance (CDC, 2011; Black, 2002).
In 2010, Hispanics accounted for the majority of the nation’s increase in
population (Passel, Cohn, & Lopez, 2011). The population increase was largely due to
migration and high birth rates among Hispanics (Lawrence, 2010). The U.S. Census
projects that people of Hispanic descent will become the largest minority group in the
country by 2050, with Mexican Americans comprising the vast majority of this group
(Passel et al., 2011). This population shift and changes in the needs of this growing
population group will likely create a demand for changes in our current health system.
Obesity and physical inactivity are major risk factors for both T2DM and GDM
(ADA, 2011; Black, 2002). Obesity is thought to induce insulin resistance and altered
glucose metabolism (Wellen & Hotamisligil, 2005). Obesity also is associated with a
state of chronic subclinical inflammation that can affect metabolic and immune pathways
(Wellen & Hotamisligil, 2005). Mexican American women are at increased risk for
obesity compared to non-Hispanic White Americans (Black, 2002). Mexican American
women of childbearing age have a high prevalence of obesity, with about 45%
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considered obese and 70% being overweight (CDC, 2011; Flegal, Carroll, Ogden, &
Curtin, 2010).
Mexican American women comprise a vulnerable population and are at
increased risk for obesity, GDM, T2DM, and psychosocial stress related to poverty,
acculturation, and acculturative stress (Gallo, Jimenez, Shivpuri, Espinosa de los
Monteros & Mills, 2010; Wellen & Hotamisligil, 2005). The projected population growth
among Mexican Americans will create an increased demand for the delivery of culturally
appropriate health care for a population that is misunderstood and vulnerable, especially
women of childbearing years. Understanding how acculturation and acculturative stress
affect childbearing Mexican American women can potentially help health care providers
establish a risk profile for earlier recognition of GDM, thus decreasing fetal exposure to
the GDM environment and decreasing or preventing future T2DM in pregnant women
with GDM and their children.
Altered Glucose Metabolism
Women who develop gestational diabetes mellitus (GDM) have up to a 60% risk
of developing T2DM later in life (ADA, 2011; Lawrence, 2010). Fetuses exposed to the
GDM environment have higher rates of obesity and are at increased risk for T2DM as
adults (Lawrence, 2010; Otero et al., 2006). Diabetes is characterized by altered glucose
metabolism that decreases the production of insulin and resistance to the existing insulin
(ADA, 2011). Pregnant women are screened for GDM during the latter part of the
second trimester, which potentially exposes the fetus to the effects of altered glucose
metabolism over the first 24–28 weeks of gestation. Although biological influences of
GDM have been studied (Lawrence, 2010; Otero et al., 2006; Wellen & Hotamisligil,
2005), little is known about psychosocial influences on GDM; specifically, chronic
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psychosocial stressors of acculturation and acculturative stress and their influence on
metabolic processes.
Mexican Americans experience increased prevalence of psychosocial stress
related to acculturation and acculturative stress, making them vulnerable to disease.
Stress in Mexican American women who are actively engaged in acculturation is
referred to as acculturative stress (Caplan, 2007). Acculturation is defined as a dynamic
and multi-faceted process by which individuals from one culture acquire traits or
acclimate to a new culture (Johnson, Carroll, Fulda, Cardarelli, & Cardarelli, 2010;
Schwartz & Zamboango, 2008). Acculturative stress is defined as the psychosocial and
physiological impact of adapting to a new culture as a result of changes in environment,
language, and finances (Torres, 2010). The impact of psychosocial stress, in particular,
distancing from extended family members and culture of origin, can potentially result in
mental health problems such as anxiety and depression (Hovey & Magana, 2000).
Physiologic stress can lead to inflammation, resulting in cell injury. Inflammation is a
cascade of biochemical reactions that attempt to heal and remove harmful stimuli and
restore cells to their normal function (McCance & Huether, 2002). Because inflammation
can cause changes in the insulin signaling pathways and result in altered glucose
metabolism, it has been implicated in diabetes (Wellen & Hotamisligil, 2005).
Physiological stress can also alter the metabolic markers of leptin and
adiponectin (Bouloumie, Curat, Miranville, & Sengenes, 2007). Leptin is a hormone
produced in white adipose tissue that has adipokine and cytokine properties (Otero et
al., 2006). As a pleiotropic hormone, it has a role in regulating energy homeostasis,
appetite, fat disposition, metabolism, and fertility (Bouloumie, Curat, Miranville, &
Sengenes, 2007; Henson & Castracane, 2005). Elavated levels of leptin are related to
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obesity, inflammation, and risk for cardiovascular disease (Bouloumie, Curat, Miranville,
& Sengenes, 2007). Leptin is released in response to the amount of energy stored in the
adipose tissue (Bluther & Mantzoros, 2004). There are leptin receptors in the brain, liver,
ovaries, and skeletal muscle that stimulate neuro-endocrine, immune, and inflammatory
responses (Otero et al., 2006; Bluther et al., 2004). Leptin plays an important role in
controlling appetite and regulating food intake by signaling satiety in the brain
(Bouloumie, Curat, Miranville, & Sengenes, 2007). Additionally, leptin acts on monocytes
and macrophages to release pro-inflammatory cytokines that can cause changes to
vasculature, oxidative stress, and platelet aggregation (Bouloumie et al., 2007).
Obesity is characterized by elevated serum leptin levels primarily due to leptin
resistance or the body’s inability to respond to leptin (Otero et al., 2006). The resistance
is related to faulty leptin transport and saturation of leptin receptors resulting in high
levels of leptin (Otero et al., 2006). Elevated leptin levels have been linked to obesity,
hypertension, diabetes, and heart disease (Bouloumie et al., 2007). During pregnancy,
elevated leptin has been linked to GDM, preeclampsia, intrauterine growth restriction,
and the fetal origins of adult disease (Henson & Castracane, 2005; Kautzky-Willer,
2001). Investigations of leptin serum concentrations across pregnancy indicate that leptin
levels are positively correlated with BMI as well as insulin resistance both before and
during the pregnancy (Henson & Castracane, 2005; Kautzky-Willer, 2001). In contrast,
another study suggested that women with GDM may exhibit lower leptin levels
compared to their healthy counterparts (Festa, Shnawa, Krugluger, Schernthaner, &
Haffner, 1999).
Adiponectin is a polypeptide hormone secreted by the adipocytes in adipose
tissue, which has anti-inflammatory, anti-atherogenic, and insulin sensitizing properties
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(Huang et al, 2007). Adiponectin prevents early inflammatory responses by preventing
the differentiation and maturation of white blood cells needed in the inflammatory
response (Huang et al, 2007). Adiponectin also affects the release and expression of
other anti-inflammatory mediators such as interleukin-10 (IL-10), which in turn limits anti-
inflammatory and immunosuppressive properties (Huang, et al., 2007). Adiponectin
further acts as an anti-atherogenic molecule by preventing aggregation of endothelial
cells and macrophages in vascular walls (Han et al., 2007). Macrophage suppression
also prevents vascular stenosis and decreases uptake of low-density cholesterol (Han et
al, 2007). Finally, adiponectin helps inhibit gluconeogenesis, which results in lower blood
glucose levels and a decrease in insulin resistance (Han et al., 2007).
High levels of adiponectin have been found to be protective against T2DM and
GDM, making adiponectin an important hormone in diabetes prevention. Dysregulation
of adiponectin and low levels of this hormone are predictive of GDM (Han et al., 2007;
Weerakeit et al, 2006). Increased adipose tissue decreases or stops the secretion of
adiponectin, which results in low adiponectin levels and loss of its beneficial properties.
Low adiponectin levels are also present in obese individuals (Han et al., 2007; Weerakeit
et al., 2006).
Purpose
The purpose of this study is twofold:
1. To explore relationships between the psychosocial stressors of acculturation
and acculturative stress in Mexican American women with and without
gestational diabetes.
2. To examine differences in the metabolic markers of leptin and adiponectin in
Mexican American women with and without gestational diabetes.
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Mexican American women comprise a vulnerable population and are at
increased risk for obesity, GDM, T2DM, and psychosocial stress related to poverty,
acculturation and acculturative stress (Gallo et al., 2010; Wellen & Hotamisligil, 2005).
Exploring whether the psychosocial factors of acculturation and acculturative stress have
an impact on metabolic markers such as gestational diabetes, leptin, and adiponectin
will aid in supporting the importance of the delivery of culturally competent care.
Significance to Nursing
Nursing is a scientific discipline that promotes the well-being of the whole person
within historical, cultural, and social contexts that shape an individual’s response to her
environment (Fitzpatrick & Whall, 1989). Leininger’s theory of transcultural nursing
(1978,1985) proposed that culturally sensitive care begins with recognizing that
individuals are the sum of their historical, cultural, and social experiences. Betty Neuman
(1982) theorized that individuals actively seek to maintain a balance in the
interrelationship of stressors and environment in order to achieve health. Any
dysregulation of this balance can lead to altered health. Struggles and disharmony can
result in negative outcomes and an inability for the individual to attain optimal health
(Fitzpatrick & Whall, 1989). Leinininger’s theory of transcultural nursing and Neuman’s
systems model can help investigate relationships between psychosocial stress (e.g.,
acculturation and acculturative stress) and metabolic alterations in leptin, adiponectin,
and gestational diabetes.
Assumptions
The following assumptions provided the foundation for this study:
1. Women are unique individuals possessing a range of normal responses to
their environment.
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2. Women desire to remain free of disease and want to promote the health of
their families.
3. Women are physiologically programmed to respond to environmental
stressors.
4. Repeated exposure to stressors alters homeostasis and physiological
processes.
5. Culture affects women’s responses to their environment.
6. The process of acculturation and acculturative stress can be stressful events
in persons not equipped or ready to confront change.
7. Acculturation and acculturative stress are psychosocial stressors.
These assumptions provided the foundation for specification of the Psychosocial
Stress and Metabolic Response in Gestational Diabetes Model. The model is based on
the allostatic load model (McEwen, 1988) and is consistent with Leininger’s theory
(1978, 1985), which states that culture and social contexts are major factors that
influence individuals’ responses to health. Neuman’s (1982) systems approach to
understanding stress responses and principles also was incorporated into the model.
The allostatic load model describes the physiological expense of a disruption of the
response systems to stress. It illustrates the physiological interrelationships that can lead
to dysregulation, which causes bodily functions to decline (McEwen, 1988). Thus, it
demonstrates that acculturation and acculturative stress are important factors that can
place individuals at risk for altered physiologic responses.
Conceptual Framework
A modified version of the allostatic load model was used to guide this
investigation of the relationships between the psychosocial markers of acculturation and
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acculturative stress, the metabolic markers of leptin and adiponectin, and their
relationship in women with and without gestational diabetes mellitus. Definitions of the
model’s concepts are presented in Table 1 and relationships among the concepts are
illustrated in Figure 1.
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Table 1.1 Definitions of Concepts Contained in the Psychosocial Stress and Metabolic Response
in Gestational Diabetes Mellitus Model
Concept Definition
Acculturation The process of transitioning and adapting from one culture into another culture.
Acculturative Stress
Stress that originates from stressors encountered during the process of acculturation, which can include anxiety, depression, feelings of marginality and alienation, heightened psychosomatic symptoms, and identity confusion.
Adaptation The biological process by which the body adjusts to repetitive external demands and threats.
Adiponectin A polypeptide hormone produced in adipose tissue that has anti-inflammatory, anti-atherogenic, and insulin sensitizing properties.
Allostasis The ability of the body to achieve homeostasis after a physiologic disruption.
Allostatic Load The physiological expense of the disruption of the response systems to stress.
Gestational Diabetes Mellitus (GDM)
Diabetes that occurs during pregnancy, generally diagnosed late in the second trimester.
Leptin A pleiotropic hormone produced in adipose tissue that plays a role in regulating energy homeostasis, appetite regulation, fat disposition, and metabolic, and fertility processes.
Metabolic Response
The physical and chemical processes that maintain body functions, including the anabolic and catabolic processes needed to sustain life.
Psychosocial Stress
Stress originating from personal, social, cultural, and external factors, and which elicit the biological response to stress.
Stress A multidimensional reaction that consists of psychosocial and physiologic factors that permit individuals to respond to a perceived threat.
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Figure 1. Psychosocial Stress and Metabolic Response in Gestational Diabetes Model adapted from the Allostatic Load Model by McEwen, 1998. Chronic psychosocial stress leads to allostatic load, creating altered metabolic responses that can lead to gestational diabetes.
12
The chronic stressors of acculturation and acculturative stress experienced by
Mexican American women were integrated into the model of physiologic phenomena of
allostasis and allostatic load to highlight their potential impact on the metabolic response
of leptin, adiponectin, and GDM. The Psychosocial Stress and Metabolic Response in
Gestational Diabetes Model proposes that repetitive activation of the stress response,
which is seen in the process of acculturation and acculturative stress, disrupts the
metabolic responses, which results in changes in leptin and adiponectin levels and
potentially increased risk for GDM. Furthermore, disruption in allostasis or balance of the
stress response creates changes in immune and metabolic processes, which places the
body at increased risk for T2DM, cardiovascular disease, and mental health problems
(McEwen, 1998).
Concepts
Gestational Diabetes Mellitus
Gestational Diabetes Mellitus was defined as diabetes that occurs during
pregnancy and is detected late in the second trimester of pregnancy, between 24 and 28
weeks gestation. Clinically, women are screened with a 1-hour 50-gm glucose tolerance
test between 24–28 weeks gestation. Women who have values greater than 139 mg/dL
require a diagnostic 3-hour glucose 100-gm tolerance test. Two elevated values out of
four are diagnostic for GDM (Kapustin et al., 2008; Esakoff, Cheng, & Caughey, 2005).
Gestational diabetes is a major risk factor for T2DM; it is estimated that 35%–60% of
women who had diabetes during their pregnancy will develop T2DM within 10 to 20
years of the pregnancy (CDC, 2011). T2DM is a metabolic disease that affects glucose
metabolism resulting in a persistent state of hyperglycemia secondary to pancreatic beta
13
cell dysfunction and the cellular resistance to the effect of insulin that can lead to
vascular and neurological complications including stroke, neuropathies, amputations,
blindness, and kidney disease (McCance & Huether, 2002).
Psychosocial stress
Stress was theoretically defined as a multidimensional reaction that consists of
psychosocial and physiologic factors that elicit a response a threat (Selye, 1973).
Stressful events are mediated by the woman’s appraisal of the threat and available
coping mechanisms, including psychosocial, social, and cultural forces that enable the
woman to respond (Glanz & Schwartz, 2008; Selye 1973). Stress occurs when the
psychosocial and physiologic demands of the threat exceed the psychosocial and
physiologic coping mechanisms potentially resulting in allostatic load (McEwen, 1998).
The stress response consists of a cascade of physiological responses that maintain the
normative environment. The hypothalamic-pituitary-adrenal axis (HPA-axis) responds
with a cascade of neuroendocrine reactions that stimulate response systems to maintain
homeostasis (Vedhara & Irwin, 2007; McEwen, 1998). Over time, the repeated demands
on the body create a path towards adaptation. Chronic stress occurs when repeated
insults maintain the HPA-axis in a state of persistent activation, which creates a
hypersensory environment that can lead to a derangement of the physiologic harmony
and result in blunted stress responses (McEwen, 1998; Selye, 1973;). The hypersensory
state also leads to allostatic load that can harm the body’s normal functions and cause
changes in glucose metabolism, fat storage, and affective processes (Vedhara & Irwin,
2007; McEwen, 1998). Chronic stressors related to work, financial burdens, and
caregiving are associated with higher allostatic load that can contribute to physiological
dysregulation in Mexican American women (Gallo et al., 2010).
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Psychosocial stress was defined as stress that originates from personal, social,
and external factors that elicit biological responses to stress. Because it causes changes
to the connectivity of brain networks, psychosocial stress has been strongly associated
with impaired affective (mood) functioning, including depression and anxiety (Liston,
McEwen, & Casey, 2009). Increased psychosocial stressors, such as maternal anxiety
during pregnancy, have been associated with altered infant development at 12 months
(Davis & Sandman, 2010). Additionally, psychosocial stress has been associated with
poor pregnancy outcomes, including increased risk for low birth weight (Hobel,
Goldstein, & Barrett, 2008). In this study, acculturation and acculturative stress were
used as indicators of psychosocial stress.
Acculturation. Acculturation was defined as the process of transitioning and
adapting from one culture into another culture (Carter-Porkras et al., 2008). During this
process, individuals experience change and are exposed to a state of stress that
requires them to use previously learned coping strategies to help them regain a state of
balance (Ward, 2006). Reaching balance may not always be possible, resulting in
altered coping mechanisms that lead to dysfunction. Acculturation among Mexican
Americans has been associated with poor health outcomes, including higher rates of
obesity, diabetes, and mental illness (Carter-Pokras, et al., 2006; Kaester, Pearson,
Keene, & Geronimus, 2009).
Acculturative Stress. Acculturative stress was defined as stress that originates
from stressors encountered during the process of acculturation. This type of stress often
includes anxiety, depression, heightened psychosomatic symptoms, identity confusion,
and feelings of marginality and alienation (Berry & Williams, 1991). Acculturative stress
can result in negative health outcomes and place individuals at risk for disease.
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Acculturative stress is a significant positive predictor for depressive symptoms that affect
well-being among college students (Iturbide, Raffaelli, & Carlo, 2009).
Metabolic Responses
Metabolic responses were defined as the physical and chemical processes that
maintain body functions, including the anabolic and catabolic processes needed to
sustain life. Chronic stress can impair normal physiologic functions and interfere with
metabolism, growth, reproduction, and immune responses (Kyrou & Tsigos, 2009).
During stress, the body is programmed to activate the HPA-axis, which results in the
release of a series of hormones that help restore homeostasis. Repetitive activation can
result in HPA-axis failure and lead to altered hormonal pathways that render the stress
response system ineffective. Chronic stress is associated with elevated cortisol levels,
which puts individuals at risk for visceral fat deposits and obesity (Anagnostis, Athyros,
Tziomalos, Karagiannis, & Mikhailidis, 2009). Visceral fat is associated with metabolic
syndrome, diabetes, and cardiovascular disease. Leptin and adiponectin are hormones
that originate from the cells of adipose tissue. In this study, the adipocytes leptin and
adiponectin were used as markers of metabolic response to evaluate if chronic stress
affects these hormones.
Leptin. Leptin was defined as a pleiotropic hormone that has a role in regulating
energy homeostasis, appetite, fat disposition, metabolism, and fertility processes
(Bouloumie, Curat, Miranville, & Sengenes, 2007; Otero et al., 2006). High leptin levels
have been associated with obesity, diabetes, and mental health problems (Bouloumie et
al., 2007). Leptin levels can be quantified by an enzyme-linked immunosorbent assay
(ELISA).
16
Adiponectin. Adiponectin was defined as a polypeptide hormone produced in
adipose tissue that has anti-inflammatory, anti-atherogenic, and insulin sensitizing
properties. Low adiponectin levels have been associated with insulin resistance,
diabetes, and atherosclerosis (Linh, Pedersen, & Richelsen, 2006). Adiponectin levels
can be quantified by an enzyme-linked immunosorbent assay (ELISA).
Concepts contained in the Psychosocial Stress and Metabolic Response in
Gestational Diabetes Mellitus Model include acculturation, acculturative stress, levels of
leptin and adiponectin, and GDM. Definitions are provided in Table 1. Relational
statements proposed by the model and depicted in Figure 1 are:
1. Psychosocial stress is related to the process of acculturation and
acculturative stress.
2. Psychosocial stress is related to allostatic load.
3. Psychosocial stress is associated with changes in metabolic response.
3. Metabolic response is associated with changes in leptin and adiponectin
levels.
4. Changes in leptin and adiponectin levels are associated with gestational
diabetes mellitus.
Research Questions
The following research questions reflective of the specific aims were posed:
Specific Aim #1: To explore relationships between the psychosocial stressors
(i.e., acculturation and acculturative stress) and metabolic markers (i.e., leptin and
adiponectin levels) in Mexican American women with and without gestational diabetes.
17
Research Question 1. Is there a significant relationship between levels of the
psychosocial markers of acculturation and acculturative stress, and levels of the
metabolic markers of leptin and adiponectin?
Specific Aim #2: To examine differences in the levels of the metabolic markers
of leptin and adiponectin in Mexican American women with and without gestational
diabetes.
Research Question 2.1. Is there a significant difference in the levels of the
psychosocial markers of acculturation and acculturative stress between women
with and without gestational diabetes?
Research Question 2.2. Is there a significant difference in the levels of the
metabolic markers of leptin and adiponectin between women with and without
gestational diabetes?
Summary
Psychosocial stressors of acculturation and acculturative stress may alter the
metabolic response over time, which can result in abnormal glucose metabolism that can
lead to GDM and to potential future T2DM. Mexican American women have a greater
prevalence of GDM and Type 2 Diabetes Mellitus than White Americans. Earlier
identification of GDM would help decrease fetal exposure to the GDM environment and
have the potential to decrease or prevent future T2DM in both mother and child.
This chapter addressed the health problem of gestational diabetes mellitus in
Mexican American women and summarized the impact of altered glucose metabolism.
The purpose of the study and its significance for nursing were presented. Assumptions
were delineated and the conceptual framework was specified. Next, key concepts were
18
defined and relationships among these concepts hypothesized. Finally, the research
questions were posed.
19
CHAPTER II
REVIEW OF THE LITERATURE
This chapter presents a review of research literature on psychosocial stress,
metabolic response, and gestational diabetes in Mexican American women of
childbearing years. An overview of the hypothalamic-pituitary-adrenal axis (HPA axis)
stress response is discussed, and the major markers for psychosocial stress in Mexican
American women (i.e., acculturation and acculturative stress) are highlighted. The major
markers for metabolic response (i.e., leptin and adiponectin) also are described.
Hypothalamic-Pituitary-Adrenal Axis
The body responds to short-term episodes of stress by the process of adaptation.
This process also is known as allostasis (McEwen, 1998). Allostasis is the body’s ability
to achieve stability after a perceived threat. The body is able to reach allostasis by
creating a stable environment during high levels of stress by activating the stress
response (McEwen, 1998). The hypothalamic-pituitary-adrenal axis (HPA axis)
stimulates stress response systems that use the neurological, cardiovascular, and
endocrine systems simultaneously to counteract threats by releasing hormones that
target specific organs (Juster, McEwen & Lupien, 2010).
The hypothalamus acts as the central regulator of the stress response and
initiates a series of interactions that lead to behavioral and peripheral changes, which
help the body readjust to a state of homeostasis (Tsigos & Chrousos, 2002). Allostasis
helps regulatory systems change over time to adapt to the demands of the environment
(Power & Schulkin, 2012). During repetitive and long-term activation of the HPA-axis,
such as that experienced in chronic stress, dysregulation occurs, which places the
response systems at risk for allostatic load.
20
Allostatic load is a state of dysfunction that results from wear and tear on the
body and brain from chronic over-activity or inactivity of the physiological systems
involved in the stress response (McEwen, 1998). This state of physiologic overload
makes the body vulnerable to disease (Power & Schulkin, 2012) and has been linked
with cardiovascular disease, T2DM, and mental health problems (Keastner, Pearson,
Keene & Geronimus, 2009). Allostatic load from chronic stress also has been implicated
in poor pregnancy outcomes including intrauterine growth restriction, preterm delivery,
and preeclampsia (Lantendreese, 2009). Repeated activation of the HPA-axis disrupts
the hormonal mechanism by failing to fully disable the stress response, taxes the body,
and maintains the body in a hypersensory state that eventually fails to reach allostasis,
leading to allostatic load. Allostatic load can be quantified by using psychosocial and
physiologic markers that help determine risk for disease (Seeman, Singer, Rowe,
Horwitz & McEwen, 1997).
Psychosocial Stress
Psychosocial stress was defined as stress that originates from personal, social,
and other external factors that elicit biological responses (Liston, McEwen, & Casey,
2009). Psychosocial stress has been strongly associated with impaired mental
functioning (e.g., depression and anxiety) that results from changes in the connectivity of
brain networks (Liston, McEwen, & Casey, 2009). Increased psychosocial stressors,
such as maternal depression and anxiety during pregnancy, have been associated with
altered infant development at 12 months (Davis & Sandman, 2010). Additionally,
psychosocial stress has been associated with poor pregnancy outcomes including
increased risk for low birth weight (Hobel, Goldstein, & Barrett, 2008).
21
Many Mexican American women who have immigrated to the United States
experience psychosocial stressors including acculturation and acculturative stress,
putting them at risk for psychosocial stress. A literature review and synthesis that
identified studies examining acculturation and acculturative stress as markers of
psychosocial stress in Hispanics including Mexican American women is summarized.
A systematic literature review was conducted to explore the information available
on acculturation and acculturative stress. The electronic search engines used to find
articles for this review were PubMed and CINAHL. The search terms used for this review
were acculturation, acculturative stress, Mexican Americans, Latinos, and Hispanic.
Using these terms, PubMed and CINAHL generated a total of 244 articles. Next, these
articles were examined for inclusion criteria, which included peer-reviewed articles and
research studies published in the past five years; this resulted in 43 articles. Next, from
these articles, those that were not peer-reviewed, that focused on animal studies,
descriptive articles, dissertations, and review articles were eliminated. After excluding
these publications, only 10 articles were identified as being relevant to this study.
Information for the studies reviewed is provided in Table 2.1.
22
Table 2.1
Summary of Studies on Acculturation and Acculturative Stress in Mexican Americans
Author, Year
Purpose Design Sample Results Conclusion
Buscemi, Williams, Tappen, & Blais, 2012
To identify relationships between acculturation and health in Hispanic elders.
Descriptive Correlational
N= 132
Acculturation had a significant positive influence on mental health but not on physical health status.
Individuals with greater acculturation reported better mental health but not physical health.
Torres, Driscoll, & Voell, 2012
To investigate the role of acculturative stress in the relationship between discrimination and distress and to examine the ability of acculturation to serve as a moderator between perceived discrimination and distress.
Cross Sectional
N = 669
Acculturative stress mediates the perceived discrimination-psychosocial distress relationship; perceived discrimination is moderated by Anglo-orientation.
Perceived discrimination was related to increased acculturative stress and psychosocial distress.
Perez-Escamilla, 2011
To examine the evidence for a link between acculturation, nutrition, and health disparities in Latinos.
Systematic Literature Review
8 studies
Associations were found between acculturation, nutrition, and health disparities..
These relationships are not linear; longitudinal studies are needed for further evaluation.
Ceballos & Palloni, 2010
To evaluate the “acculturation paradox” and investigate the selective return migration hypothesis on birth outcomes.
Cross Sectional
N = 539
Length of stay in the U.S. had a significant, nonlinear relationship with birth outcomes; acculturation was not significantly relationship to birth outcomes.
The “Acculturation Paradox” has little effect on birth outcomes. Birth outcomes are more likely affected by the selective return migration mechanism.
23
Table 2.1 continued
Summary of Studies on Acculturation and Acculturative Stress in Mexican Americans
Author, Year Purpose Design Sample Results Conclusion
Johnson, Carroll, Fulda, Cardarelli, & Cardarelli, 2010
To investigate the relationship between acculturation and self-reported health.
Cross Sectional
N = 135
Mexican-oriented participants were about 3 times more likely to report fair to poor self-reported health compared to Anglo-oriented participants.
Acculturation levels in Mexican Americans had an effect on their self-reported health.
Negy, Hammons, Reig-Ferrer, & Carper, 2010
To examine the relationship between acculturative stress and marital distress in immigrant women and explore acculturation, ethnic identity, and social support.
Cross Sectional
N = 95 Acculturative stress was significantly associated with higher marital distress; acculturative stress significantly predicted marital distress, while social support mediated the relationship between acculturative stress and marital distress.
Social support is an important factor in acculturative stress and marital distress.
Torres, 2010 To investigate the ability of acculturation, acculturative stress, and coping to predict different levels of depression in Latinos.
Cross Sectional
N = 148
The high depression group significantly endorsed an Anglo orientation and English competency.
The pressures and demands of acculturation pose an increased risk for mental health problems.
24
Table 2.1 continued
Summary of Studies on Acculturation and Acculturative Stress in Mexican Americans
Author, Year
Purpose Design Sample Results Conclusion
Iturbide, Raffaelli, & Carlo, 2009
To investigate whether different ethnic identity components moderate the association between acculturative stress and psychosocial adjustment in Mexican American college students.
Cross Sectional
N = 148
Ethnic affirmation/belonging moderated the relationship between acculturative stress and depression; acculturative stress was negatively correlated with self-esteem and positively with depression.
Acculturative stress is an important factor to consider when evaluating well-being of Mexican origin college students.
Campos, Schetter, Walsh & Schenker, 2007
To examine whether Mexican and Anglo orientation in pregnant women demonstrate different patterns associated with stress, pregnancy anxiety, and infant birth weight.
Cross Sectional
N = 1064
Acculturation was significantly associated with greater perceived stress, but was not significantly associated with pregnancy anxiety and low birth weight.
Acculturation is multidimensional and is influenced by other psychosocial factors.
Carter-Pokras, 2008
To compare health status indicators between U.S. and Mexican-born Mexican Americans using proxy measures of acculturation.
Systematic Literature Review
90 studies
U.S.-born Mexican Americans have higher morbidity and mortality compared to Mexico-born immigrants.
The longer individuals reside in the U.S. the more likely they are to engage in behaviors that are not health promoting.
25
Stress in Mexican American Women
Acculturation
Acculturation is a multidimensional process that occurs when individuals who are
transitioning into a new culture attempt to adopt the cultural traits and social patterns of
the dominant culture (Carter Porkras et al., 2008; Hovey, 2000). As they experience the
acculturation process, women undergo a state of stress and use previously learned
coping strategies to help them regain a state of balance (Ward, 2006). However, these
previously learned coping strategies may not always be sufficient to help women adapt
to the new environment. As a result, they may be forced to find new coping mechanisms,
which, in turn, can create chaos and disharmony as they slowly transition into the new
culture. Acculturation among Mexican Americans has been associated with poor health
outcomes including higher risk for obesity, mental distress, and diabetes (Carter-Pokras
et al., 2008; Kaester, Pearson, Keene, & Geronimus, 2009). In contrast, some
researchers have concluded that although more acculturated individuals may not report
better physical health, some report better mental health compared to less acculturated
individuals (Buscemi, Williams, Tappen, & Blais, 2012).
Acculturation also has been linked to depression and systemic inflammation
(Raison, Capuron, & Miller, 2006). Evidence suggests that more acculturated women
have a higher risk for depression, inflammation, and obesity (Ruiz, Stowe, Goluszko,
Clark, & Tan, 2007). A study that investigated acculturation and depression in Latinos
concluded that those experiencing higher levels of depression significantly endorsed an
Anglo orientation and reported greater English competency (Torres, 2010). The author
concluded that the pressures and demands of acculturation increase the likelihood of
mental health problems in this population.
26
Other studies have suggested that the relationship between acculturation and
health outcomes was not as clear. A study that evaluated acculturation, nutrition, and
health disparities in Latinos concluded that acculturation is associated with poor diet and
obesity. The author, however, was not convinced that these results were due to
acculturation, but rather may have been the result of other socioeconomic and
demographic factors such as income and nativity (Perez-Escamilla, 2011). He also
concluded that the relationship was not linear and required further evaluation through
longitudinal studies and more sophisticated statistical techniques.
Indicators of health status of U.S. and Mexico-born Mexican Americans vary, with
U.S.-born Mexican Americans having higher morbidity and mortality rates compared with
Mexico-born immigrants (Carter-Porkras, 2008). The authors believe that the longer
individuals reside in the U.S., the more likely they are to engage in behaviors that are not
health promoting including excess alcohol use, smoking, and drug use. Ceballos and
Palloni (2010) proposed that the negative effects seen with acculturation, specifically
related to birth outcomes, were due to the selective return hypothesis. This hypothesis
suggests that because healthier women are more likely to migrate these women also
have better birth outcomes because they began their pregnancy in better health.
Similarly, unhealthy women are more likely to stay in one place longer and exhibit poor
health outcomes because they were already in poor health. Migration may be a
demanding and possibly difficult event that those in good health are more likely to
consider.
In a study that examined acculturation as a moderator between perceived
discrimination and distress, the authors found that perceived discrimination is moderated
by Anglo behavioral orientation but not by Latino behavioral orientation (Torres, Driscoll,
27
& Voell, 2012). Anglo behavioral orientation is consistent with higher level of
acculturation and longer U.S. residence. Furthermore, a study that evaluated
relationships between acculturation and health in Hispanic elders aged 55-98 found that
acculturation had a significant influence on mental health status but not on physical
health status (Buscemi, Williams, Tappen, & Blais, 2012). In their study, individuals with
greater levels of acculturation reported better mental health but not physical health
although the literature reports that more acculturated Hispanics have better health
practices (Buscemi, Williams, Tappen, & Blais, 2012). Similarly, when investigating the
relationship between acculturation and self-reported health in Mexican Americans,
Mexican-oriented subjects were about three times more likely to report fair to poor health
as Anglo-oriented subjects (Johnson, Carroll, Fulda, Cardarelli, & Cardarelli, 2010). The
study concluded the process of acculturation and possibly the process of adapting to the
new environment resulted in perceptions of poor health.
Acculturative Stress
Acculturative stress was defined as stress that originates from stressors
encountered during the process of acculturation; it often includes anxiety, depression,
feelings of marginality and alienation, heightened psychosomatic symptoms, and identity
confusion (Berry & Williams, 1991). Acculturative stress can place individuals at risk for
negative health outcomes. Acculturative stress has been found to be a significant
positive predictor for depressive symptoms among college students when exploring
psychological factors that affect well-being (Iturbide, Raffaelli, & Carlo, 2009). In a study
that investigated the role of acculturative stress in perceived discrimination and
psychosocial distress, the authors (Torres, Driscoll, & Voell, 2012) found that
acculturative stress mediated the perceived discrimination-psychosocial distress
28
relationship. They concluded that perceived discrimination was related to increased
acculturative stress and psychosocial distress.
The process of acculturation is challenging, makes individuals feel vulnerable,
and places them at risk for acculturative stress. Acculturative stress can negatively affect
family relationships. A study that investigated the relationship between acculturative
stress and marital distress in immigrant women and explored acculturation, ethnic
identity, and social support found that acculturative stress was significantly associated
with and was a significant predictor of higher marital distress (Negy, Hammons, Reig-
Ferrer, & Carper, 2010). These authors also found that social support mediated the
relationship between acculturative stress and marital distress. These findings highlight
the importance of evaluating acculturative stress as a potential risk factor for altered
family functioning.
Hovey and Magana (2000) associated high levels of acculturative stress with
anxiety and depression in Mexican farm workers. Finch, Hummer, Kolody, and Vega
(2001) found that acculturative stress resulting from discrimination contributed to
negative ratings of health. The study concluded that individuals who experience
acculturative stress report not feeling well.
Allostatic load has been linked to chronic stress and has been implicated in
cardiovascular disease, T2DM, and mental health problems (Keastner, Pearson, Keene
& Gernonimus, 2009). Psychosocial stress, such as seen with acculturation and
acculturative stress, is a form of chronic stress (Berry & Sam, 1997) that can potentially
lead to allostatic load causing a derangement of the stress response (McEwen, 1998).
Although studies continue to explore the effects of acculturation and acculturative stress,
there is sufficient evidence to support that this form of psychosocial stress can have
29
negative effects, indicating that further studies are needed to explore whether
acculturation and acculturative stress can place the body in a state of allostatic load.
Metabolic Response to Stress
Metabolic responses were defined as physical and chemical processes that
maintain bodily functions, including anabolic and catabolic processes needed to sustain
life. Chronic stress can impair normal physiologic functions and interfere with
metabolism, growth, reproduction, immune response, and mental health (Kyrou &
Tsigos, 2009). During stress, the body is programmed to activate the HPA-axis, which
results in the release of a series of hormones that help restore homeostasis. Repeated
activation of the HPA-axis can result in hormonal failure and lead to altered hormonal
pathways that render the stress response system ineffective. Chronic activation of the
HPA-axis results in altered metabolic responses that lead to increased visceral adiposity
and decreased lean body mass (Tsigos & Chrousos, 2002). Chronic stress also is
associated with elevated cortisol levels, which place an individual at risk for visceral
adipose accumulation (Anagnostis, Athyros, Tziomalos, Karagiannis, & Mikhailidis,
2009), a condition that is associated with metabolic syndrome, diabetes, and
cardiovascular disease. Because leptin and adiponectin are hormones that originate
from the cells of adipose tissue, an increase in visceral adiposity may place persons at
risk for altered metabolic status. In the current study, the adipocytes leptin and
adiponectin were used as markers of the metabolic response to evaluate whether
chronic stress affects these hormones.
Women who develop GDM are in an altered metabolic state marked by
subclinical inflammation years before they exhibit signs and symptoms of disease, which
places them at risk for altered glucose metabolism, metabolic syndrome, and
30
cardiovascular disease (Di Cianni, 2007; Winzer, et al., 2004). Women who previously
had GDM have evidence of endothelial dysfunction, which is associated with insulin
resistance and pro-inflammatory cytokines (Winzer et al., 2004). Additionally, because
the level of insulin resistance and production is greatly affected by body mass, obese
women have greater insulin resistance than normal weight women (Volpe et al., 2007).
Obesity is a major contributing factor for GDM and is related to pro-inflammatory and
angiopathy processes (Winzer, 2004). There is evidence that pro-inflammatory cytokines
are present in adipose tissue, which significantly increases inflammation and risk for
insulin resistance, GDM, and T2DM (Wellen & Hotamisligil, 2005; Dandona et al., 2004).
Some markers implicated in both GDM and T2DM are the adipokines leptin and
adiponectin.
A systematic literature review and synthesis was conducted to explore the
information available on the relationship of the adipokines leptin and adiponectin and
GDM. The electronic search engines used to find articles for this review were PubMed
and CINAHL. The search terms used for this review were leptin, adiponectin, and
gestational diabetes. PubMed and CINAHL generated a total of 54 articles on this topic.
Inclusion criteria encompassed peer-reviewed articles and research studies published in
the past 10 years. Articles that were not peer-reviewed, animal studies, descriptive
articles, dissertations, and review articles were not included. After excluding all studies
that did not meet the desired criteria, only 13 articles were identified as being relevant to
this study. Information for the studies reviewed is provided in Table 2.2.
31
Table 2.2
Summary of Studies Investigating Leptin and Adiponectin in Gestational Diabetes
Author, Year Purpose Design Sample Results Conclusion
Lopez-Tinoco et al., 2012
To evaluate the relationships between cytokine concentrations, components of metabolic syndrome, and cardiovascular risk in women with GDM.
Case Control
N = 126 n = 63 cases n = 63 controls
Women with GDM had significantly higher BMIs, higher levels of leptin, and significantly lower levels of adiponectin.
Women with GDM have a cytokine profile that includes high concentrations of leptin, low levels of adiponectin, and higher pre-gravid weight.
Skavarca, Tomazic, Krhin, Blagus & Janez, 2012
To evaluate associations between concentrations of adipokines and insulin resistance at different stages of glucose tolerance.
Cross Sectional
N = 74 n = 25 normal n = 19 intermediate glucose tolerance n = 30 GDM; Evaluated at 24–28 weeks gestation
There were significant differences in insulin resistance between the three groups. No significant differences were seen in adipokine concentrations.
Adiponectin and leptin were not associated with degree of glucose tolerance in pregnancy.
Horosz, Bomba-Opon, Szymanska, Wielgos, 2011
To compare adiponectin, leptin, and insulin resistance in women with and without gestational diabetes.
Case Control
N = 134 n = 86 cases n = 48 controls
Adiponectin levels were significantly lower in the GDM group; leptin levels were not significantly different between the groups; insulin resistance was significantly higher in the GDM group.
Women with GDM have lower levels of adiponectin and higher levels of insulin resistance.
32
Table 2.2 continued
Summary of Studies Investigating Leptin and Adiponectin in Gestational Diabetes
Author, Year
Purpose Design Sample Results Conclusion
Saucedo et al., 2011
To investigate the relationship between adipokines and insulin resistance during pregnancy and PP in women with GDM.
Prospective Longitudinal
N = 120 n = 60 GDM women n = 60 healthy women; Evaluated at 30 weeks gestation, and at 6 weeks and 6 months PP
GDM women had higher insulin resistance compared to healthy controls. No differences in levels of adipokines were seen during pregnancy, at 6 weeks, and at 6 months PP. Women with GDM had persistent leptin and insulin resistance; progressively impaired glucose tolerance was found in women with prior GDM.
Women with prior GDM have higher levels of insulin resistance, higher levels of leptin, and glucose intolerance.
Retnakaran et al., 2010a
To evaluate the risk of early progression to pre-diabetes and diabetes in women with varying levels of glucose intolerance in pregnancy.
Prospective Longitudinal
N = 325 Evaluated at 3 months and 12 months PP
At 12 months, 10% of the subjects progressed to impaired glucose tolerance, compared to 17% with prior GDM. At 3 months, although all had NGT, progressors had higher BMIs and leptin levels and lower adiponectin levels.
Normal glucose tolerance test at 3 months PP does not provide assurance of low risk for pre-diabetes progression.
33
Table 2.2 continued
Summary of Studies Investigating Leptin and Adiponectin in Gestational Diabetes
Author, Year
Purpose Design Sample Results Conclusion
Retnakaran et al., 2010b
To evaluate if adiponectin, leptin, and CRP levels during pregnancy are related to PP metabolic defects that link GDM with T2DM.
Prospective Longitudinal
N = 487 n = 137 GDM n = 91 IGT n = 259 NGT Evaluated at 28–31 weeks gestation and 3-months PP
Adiponectin levels were lowest and CRP levels highest in women with prior GDM; no differences were found in leptin levels. Low adiponectin levels were also related to PP beta cell function and predicted PP insulin sensitivity and beta cell function.
Low adiponectin levels during pregnancy predict insulin resistance, beta cell function, and fasting glucose and may play a role in the progression of GDM to T2DM.
Choi et al., 2008
To investigate if adipokine concentrations are associated with abnormal glucose tolerance in women with prior GDM.
Cross Sectional
N = 157 n = 17 NGT n = 72 GDM NGT n = 60 GDM IGT n = 8 GDM-DM Evaluated at 2 months PP
Adiponectin levels were the lowest in the GDM DM group and were inversely correlated with parameters of insulin resistance. No differences were found in leptin levels.
Severity of glucose intolerance in women with prior GDM is associated with low adiponectin levels.
Xue-Lian, Hui-xia & Yi, 2008
To investigate which occurs first in GDM— changes
in adipokines or abnormal glucose metabolism.
Nested Case Control
N = 32 n = 22 GDM n= 10 GIGT n = 20 Healthy controls; Evaluated at 14–20 weeks gestation
Women with GDM had significantly higher levels of leptin and lower levels of adiponectin.
Changes in adipokines occurred prior to evidence of altered glucose metabolism.
34
Table 2.2 continued
Summary of Studies Investigating Leptin and Adiponectin in Gestational Diabetes
Author, Year
Purpose Design Sample Results Conclusion
Pirc et al., 2007
To compare concentrations of glucose, insulin, leptin, and adiponectin in umbilical cord blood of babies of women without GDM, mild GDM without treatment, and mild GDM with treatment.
Randomized Controlled Trial
N = 228 n = 36 Mild GDM Treatment n = 49 Mild GDM Routine Care n = 133 Controls
Cord plasma glucose was statistically higher in women receiving routine care compared to controls; cord serum insulin and insulin to glucose ratio were similar in the 3 groups; leptin was statistically lower in the GDM treated group compared to routine care, and significantly different in controls. Adiponectin was lower in both GDM groups compared to controls.
Fetal adipo-insular (fat-insulin) axis is affected by treatment in women with mild GDM.
Ategbo et al., 2006
To investigate hormone and cytokine profile of macrosomic babies born to mothers with GDM.
Case Control
N = 119 n = 59 GDM cases n = 60 controls Mothers with GDM and newborns were evaluated immediately after delivery and aged matched with healthy women and newborns
Women with GDM had lower adiponectin levels and higher levels of leptin and inflammatory cytokines.
GDM is linked to down regulation of adiponectin and up regulation of leptin and inflammation. Fetal macrosomia is associated with down-regulation of adipokines.
35
Table 2.2 continued
Summary of Studies Investigating Leptin and Adiponectin in Gestational Diabetes
Author, Year Purpose Design Sample Results Conclusion
McLachlan, O’neal, Jenkins & Alford, 2006
To investigate the role of adiponectin, TNF-α, leptin, and CRP in insulin resistance in pregnancy and relationship to insulin secretion and action.
Case Control N = 38 n = 19 cases n = 19 controls
Only leptin was correlated with SI; no changes were seen with adiponectin.
The influence of leptin and adiponectin on SI might be attributed to other factors in pregnancy.
Winzer et al., 2004
To investigate plasma concentration of parameters of subclinical inflammation and adipocytokines in women with pGDM at both 3-and 12-months post- delivery.
Cross Sectional; Prospective Longitudinal
N = 108 n = 89 women with pGDM at 3 and 12 months post-delivery n = 19 normal controls
Women with pGDM had lower levels of adiponectin, decreased insulin sensitivity, but increased leptin levels and subclinical inflammation parameters.
Women with pGDM have lower concentrations of adiponectin independent from degree of obesity and insulin sensitivity.
Ranheim et al., 2004
To evaluate if adiponectin represents a link between endocrine function of adipose tissues and GDM by comparing levels in women with and without GDM.
Case Control N = 51 n = 22 cases n = 29 controls
Women with GDM had lower levels of adiponectin compared to non-GDM women. Leptin levels did not differ between the groups.
Low adiponectin is associated with GDM.
Note: BMI = body mass index; CRP = c-reactive protein; GDM = gestational diabetes mellitus; GDM-DM =
type 2 diabetes after gestational diabetes; GIGT = gestational impaired glucose tolerance; IGT = impaired
glucose tolerance; NGT = normal glucose tolerance; pGDM = prior gestational diabetes mellitus; PP =
postpartum; SI = insulin sensitivity; TNF-α = tumor necrosis factor – alpha; T2DM = type 2 diabetes mellitus;
Wks = weeks
36
Leptin
Leptin is a hormone secreted by adipose tissue that plays a role in regulating
energy homeostasis, appetite regulation, fat disposition, and metabolic and fertility
processes (Bouloumie, Curat, Miranville, & Sengenes, 2007; Henson & Castracane,
2005). Leptin has an influence on several bodily functions, including the hypothalamus,
pancreas, liver, and skeletal and adipose tissues. In the hypothalamus, leptin acts as a
satiety (fullness) signal and alerts the body to regulate food intake and energy
expenditure. In skeletal, adipose and liver tissues, leptin acts on fatty acid oxidation,
lipolysis, and lipogenesis. In the pancreas, leptin modulates insulin secretion. Leptin
further plays a role in inflammation by altering vascular wall reaction and platelet
aggregation; it also has pro-inflammatory and immune-stimulatory effects (Bouloumie,
Curat, Miranville, & Sengenes, 2007). Elevated leptin is associated with obesity and is
positively correlated with BMI (Fried, Ricci, Russell, & Laferrere, 2000). In pregnancy,
leptin levels progressively increase with gestation, and the rise in leptin levels is
correlated with the rise of the pregnancy hormone human chorionic gonadotropin
(Henson & Castracane, 2006).
During pregnancy, elevated leptin levels have been linked to GDM,
preeclampsia, intrauterine growth restriction, and the fetal origins of adult diabetes
(Henson & Castracane, 2005; Kautzky-Willer, 2001). In a study in women with GDM that
evaluated the relationships between cytokine concentrations, components of metabolic
syndrome, and cardiovascular risk, women with GDM had significantly higher BMIs and
higher levels of leptin, an indication of altered metabolic status and a potential link to
metabolic and cardiovascular disease (Lopez-Tinoco et al., 2012).
37
In contrast, in a study that evaluated associations between concentrations of
adipokines and insulin resistance at different stages of glucose tolerance in pregnant
women, the authors did not find significant differences in adipokine concentrations. They
concluded that adipokines were not associated with the degree of glucose tolerance in
pregnancy (Skavarca, Tomazic, Krhin, Blagus & Janez, 2012). Similarly, in a study that
investigated the role of adiponectin, TNF-α, leptin, and CRP in insulin resistance in
pregnancy and their relationship to insulin secretion and action, the researchers
concluded that leptin and adiponectin may not be the primary factors influencing insulin
sensitivity, but rather that insulin resistance may be caused by other factors related to
the pregnancy (McLachlan, O’Neal, Jenkins & Alford, 2006). Further, in a study that
compared leptin and insulin resistance in women with and without gestational diabetes,
although leptin was not found to be significantly different in the two groups, insulin
resistance was significantly higher in the GDM group (Horosz, Bomba-Opon,
Szymanska, Wielgos, 2011). Another study that investigated the relationship between
adipokines and insulin resistance during pregnancy and the postpartum period reported
that women with GDM had higher insulin resistance compared to normal women and did
not find differences in adipokines between the two groups during pregnancy (Saucedo et
al., 2011). However, these researchers did find that at six weeks and six months
postpartum, the women who had GDM had persistently elevated leptin concentrations,
insulin resistance, and glucose intolerance. These findings support the need for long-
term investigation of the role of leptin on insulin resistance and glucose intolerance in
women who experienced prior GDM.
38
Adiponectin
Adiponectin is a protein secreted by adipose tissue that has a role in glucose
regulation and insulin resistance. It has anti-inflammatory, anti-atherogenic, cardio-
protective, and insulin sensitizing properties that may be protective against obesity-
related diseases including T2DM (Szmitko, Teoh, Stewart, & Verma, 2007; Wellen &
Hotamisligil, 2005). Adiponectin helps to maintain a healthy vascular system and has
protective effects against endothelial dysfunction, plaque initiation and progression, and
plaque rupture and thrombosis. In contrast, low adiponectin levels promote vasculature
dysfunction by activating endothelial damage, plaque formation and progression, as well
as rupture and thrombosis of plaques. Adiponectin’s insulin sensitizing properties are
related to its ability to reduce tissue triglyceride content and up-regulation of insulin
signaling, which results in improved insulin sensitivity in the liver and skeletal muscles
(Kadowaki & Yamauchi, 2005).
Studies have suggested that low levels of adiponectin are predictive of GDM,
while higher levels may be protective against GDM (Weerakeit et al, 2006). Studies have
demonstrated that obesity, which is often characterized by an inflammatory process, is
marked by low adiponectin levels (Lopez-Tinoco et al.; Weerakeit et al., 2006). Lower
levels of adiponectin have been reported in women with prior GDM. A study that
measured adiponectin concentrations in the first trimester of pregnancy to identify a
relationship for subsequent GDM found that women who developed GDM exhibited
lower levels of adiponectin at 11 weeks and 28 weeks gestation (Georgiou et al., 2008).
Heitritter et al. (2004) reported similar findings in women one year after a pregnancy
complicated by GDM. They found that women with prior GDM had lower levels of
adiponectin compared to women without prior GDM. Both of these studies suggest that
39
lower levels of adiponectin are associated with altered glucose metabolism, which is
likely due to the loss of its beneficial glucose regulating functions.
A study that compared adiponectin and insulin resistance in women with and
without gestational diabetes found that adiponectin was significantly lower and insulin
resistance was significantly higher in the GDM group (Horosz, Bomba-Opon,
Szymanska, & Wielgos, 2011). These findings are consistent and support that low
adiponectin levels are associated with loss of insulin regulating properties. A longitudinal
study that evaluated the risk of early progression to pre-diabetes and diabetes in women
with varying levels of glucose intolerance during pregnancy reported that at three
months postpartum, women with prior GDM had higher BMIs, higher levels of leptin, and
lower levels of adiponectin; all the study participants had normal glucose tolerance. In
addition, at 12 months postpartum, 10% of the study population progressed to impaired
glucose tolerance, compared to 17% of participants with prior GDM. The researchers
concluded that the normal glucose tolerance test at 3 months postpartum does not
provide assurance of low risk for pre-diabetes progression (Retnakaran et al., 2010a).
When evaluating whether adiponectin, leptin, and c-reactive protein (CRP) levels
during pregnancy are related to postpartum metabolic defects that link GDM with T2DM,
studies have found that adiponectin levels were lowest and CRP levels were highest in
women with prior GDM. Low adiponectin levels also were related to postpartum beta cell
function and predicted postpartum insulin sensitivity and beta cell function (Retnakaran
et al., 2010b). These findings suggest that low adiponectin levels during pregnancy may
be predictive of factors that play an important role in the progression of GDM to T2DM.
40
Gestational Diabetes
Gestational diabetes was defined as diabetes that occurs during pregnancy.
GDM generally is detected late in the second trimester of pregnancy between 24 and 28
weeks of gestation. Clinically, women are screened with a 1-hour 50-gm glucose
tolerance test at between 24 and 28 weeks gestation. Women with values greater than
139 mg/dL require a diagnostic 3-hour glucose 100-gm tolerance test. Two elevated
values out of four tests are diagnostic for GDM (Kapustin et al., 2008; Esakoff, Cheng, &
Caughey, 2005). Because gestational diabetes complicates a pregnancy, requires strict
management to avoid maternal and fetal complications. Women with GDM have an
increased risk for preeclampsia, shoulder dystocia, and cesarean section delivery
(Hayes, 2009). Fetal complications include fetal macrosomia (birth weight 4000 grams or
greater), neonatal hypoglycemia (blood sugar less than 45 ng/dL), congenital
abnormalities, increased risk for prenatal mortality, and risk for obesity and T2DM as
adults (Kapustin et al., 2008). To manage this condition, women require intensive
counseling on diet, glucose monitoring, weight management, and recommended
physical activities. Women who are not able to maintain and control their recommended
glucose levels will require medical management including oral medication or insulin.
Women who develop GDM have an altered metabolic state marked by subclinical
inflammation for years before they develop signs and symptoms of diabetes, which puts
them at risk for altered glucose metabolism, metabolic syndrome, and cardiovascular
disease (Di Cianni, 2007; Winzer et al., 2004). Women with previous GDM also have
evidence of endothelial dysfunction, which is associated with insulin resistance and pro-
inflammatory cytokines (Winzer et al., 2004). In addition, because the level of insulin
41
resistance and production is greatly affected by body mass, obese women have greater
insulin resistance than normal weight women (Volpe et al., 2007).
There also is evidence that pro-inflammatory cytokines are present in adipose
tissue, significantly increasing inflammation and risk for insulin resistance, GDM, and
T2DM (Wellen & Hotamisligil, 2005; Dandona et al., 2004). Some markers implicated in
GDM and T2DM are the adipokines leptin and adiponectin. A study that investigated the
temporal order changes in adipokines and abnormal glucose metabolism found that
women with GDM had significantly higher levels of leptin and lower levels of adiponectin
and that these changes occurred prior to evidence of altered glucose metabolism or
GDM (Xue-Lian, Hui-xia & Yi, 2008).
Metabolic responses are essential to meet the physiological demands of the
body (Kyrou & Tsigos, 2009). Leptin and adiponectin are two adipokines that are known
to contribute to metabolic responses and which have been associated with metabolic
alterations including obesity and glucose metabolism (Kyrou & Tsigos, 2009). Chronic
stress has been known to contribute to increases in cortisol, the stress hormone that has
been known to increase visceral adipose tissue, potentially altering the normal metabolic
responsibilities of these hormones (Anagnostis, Athyros, Tziomalos, Karagiannis, &
Mikhailidis, 2009). The literature supports that alterations in leptin and adiponectin are
found in women with GDM and glucose intolerance.
Summary
Studies on acculturation and acculturative stress suggest that both acculturation
and acculturative stress are life altering experiences that can place individuals at risk for
chronic stress. Studies on leptin and adiponectin suggest that alterations in these
metabolic hormones can yield disruption of the normal physiology of the body. Although
42
there is extensive literature on how each of these concepts affects individuals and
human physiology, little is known about how the chronic stressors of acculturation and
acculturative stress, in combination with changes in the metabolic markers of leptin and
adiponectin, may affect or contribute to gestational diabetes mellitus and altered
metabolic function indicating allostatic load. Thus, this study intends to explore the
relationships between psychosocial stress and metabolic response in Mexican American
women with and without gestational diabetes.
This chapter presented a review of research literature addressing psychosocial
stress, metabolic response, and gestational diabetes in Mexican American women of
childbearing age. An overview of the HPA-axis stress response was discussed, and the
major markers for psychosocial stress in Mexican American women (e.g., acculturation
and acculturative stress) were highlighted. The major markers for metabolic response—
leptin and adiponectin—were described. Gestational diabetes in Mexican American
women of child-bearing years was reviewed.
43
CHAPTER III
METHODS
This chapter addresses the research approach and methodology used in this
study. Institutional Review Board approval, research design, sampling and recruitment
procedures, and informed consent are discussed. Procedures for data collection,
analyses and interpretation of results are described. Finally, potential threats to validity
are acknowledged and addressed.
Institutional Review Board Approval
Institutional Review Boards (IRBs) develop protocols to protect the ethical issues
that can arise when conducting research (Sieber & Stanley, 1988). Conducting
responsible research consists of having respect, integrity, and protecting research
ethics. Ethical considerations in research include having voluntary participation of
subjects, informed consent, confidentiality, anonymity, and explaining any potential
harms of the study (Polonski & Waller, 2005). In this study, these ethical considerations
were considered as part of the parent study as well as the secondary analysis and
efforts were made to comply with IRB policies. The principal investigator of the parent
study, Dr. Jeanne Ruiz, received IRB approval from the University of Texas at Austin.
For this study, IRB approval was resubmitted and obtained for the secondary analysis.
Research Design
The research design describes the methodology and procedures that will be
used to address the research questions of interest. The current study was a secondary
analysis of the prospective, observational study funded by the National Institutes of
Health #5R01NR007891, “Preterm Birth: Psychoneuroimmunology in Hispanics,” which
was conducted by Dr. Jeanne Ruiz. The purpose of the study was to examine the impact
44
of acculturation in Hispanic women on preterm birth and to assess the role of
psychosocial, physiologic, and genetic mediating factors for explaining the relationships
between acculturation and birth outcomes.
A secondary analysis is research to address new questions that is conducted on
data already collected by another researcher and reanalyzed to address those additional
questions (Polit & Tatano Beck, 2008). A case-control, descriptive, correlation design
was used to address the current research questions. A purposive sample of Mexican
American women aged 14–45 who were between 22 and 24 weeks pregnant was
recruited for the parent study.
Sampling Procedures
The parent study used a non-probability convenience sampling procedure to
recruit a total of 518 study participants. Participants in the parent study were pregnant
Mexican American women who had resided in the United States for at least 10 years
and who were receiving their obstetrical care at obstetrical clinics in east and central
Texas. Women who had lived in the U.S. for fewer than 10 years were excluded
because previous studies have found that consistent with the “Hispanic Paradox,”
women who had recently immigrated had similar or better health outcomes than the non-
Hispanic white population (Palloni & Morenoff, 2001; Franzini; Ribble, & Keddie, 2000).
Inclusion criteria for the parent study included the following:
Ability to provide informed consent
Ability to read and speak English or Spanish
Pregnant at 22–24 gestational weeks with a singleton, intrauterine pregnancy as
confirmed by accurate last normal menstrual period or ultrasound to confirm
dating
45
Self-identified as Hispanic
Age between 14–45 years
If age 17 or younger, ability to obtain parental consent
Exclusion criteria for women included:
Inability to read either English or Spanish
Known uterine or cervical abnormalities
Multiple gestations: twins or triplets
Kidney disease, pyelonephritis in the current pregnancy, or chronic hypertension
Heart disease, coronary artery disease, history of peri-partum cardiomyopathy
Autoimmune disorders: lupus, antiphospholipid syndrome
Type 1 or Type 2 diabetes
Asthma requiring use of steroid inhaler
Pre-eclampsia at time of data collection
Oral steroid use one month prior to the time of enrollment
Congenital anomalies as determined on fetal ultrasound, especially those leading
to hydramnios, trisomies, major structural anomalies as neural tube defects,
ventral wall defects, or congenital heart disease
Blood group isoimmunization
Active cervico-vaginal bleeding or placenta previa
Self-report of an ethnicity other than Hispanic
Previous participation in the study.
Case-control Sample
The secondary analysis consisted of a case-control design where GDM cases
from the parent study were matched and compared with non-GDM cases. The database
46
from the parent study was examined and using a chart audit, participants who had GDM
were selected. Next, a new database was created, and the 38 participants with GDM
were manually matched according to age and BMI to participants who did not develop
GDM during the pregnancy. The total sample for the sub-study included 76 participants
aged 21–43 years. No minors were included in the sub-sample since there were no
participants with GDM younger than 18 years of age.
Recruitment of Subjects for the Parent Study
Clinic staff, nurses, nurse practitioners, and physicians at participating obstetrical
clinics in east and central Texas were asked to direct potential participants who were
less than 22 weeks pregnant to the bilingual recruiter. The trained recruiter approached
potential participants during their obstetric visit to ask about their interest in participating
in the study. If the participant agreed, the recruiter provided the potential eligible
participants with the telephone number to enroll in the study and scheduled a time for
the data collection appointment. The research office telephone was managed by the
research nurse, who would further screen the interested participants, determine
eligibility, and confirm the appointment for data collection.
Securing Informed Consent
Informed consent is an ethical principal requiring researchers to disclose
potential risks and benefits involved in the propose study (Polit & Tatano Beck, 2008).
Informed consent should include disclosure, capacity, and voluntary participation.
Consent was received from the participants for the parent study according to IRB
protocol. IRB-approved consent forms were provided to all potential study participants.
Potential participants were required to read the first two lines of the consent to the
recruiter to verify literacy. Participants then were given the opportunity to read the
47
consent form themselves or have the research nurse read the consent form to them. For
participants younger than 18 years of age, assent was obtained from the participant and
consent was obtained from their parent. The research nurse was available to answer
any questions regarding the study. The secondary analysis conducted for this study did
not include participants younger than 18 years of age.
Ethical Considerations
Protecting Human Rights of Subjects. A major responsibility of all researchers
is to protect the human rights of study subjects. Researchers must abide by the
guidelines set forth by the Belmont Report, which delineates important ethical principles
needed for the conduct of responsible research. These principles include respect for
persons, beneficence, and justice (Belmont Report, 1979). Research participation should
at all times be voluntary with participants viewed as autonomous; if autonomy is to be
lost, special consideration for protection should be considered. To protect confidentiality
of the potential subjects, participants for the parent study were approached for
discussion regarding the study only in private areas and only those individuals who were
interested were enrolled. All participants were informed that participation in the study
was voluntary and that they could withdraw from the study at any time. Contact
information and demographic information for participants was obtained in a private
office. Data were collected in a private examination room to ensure maximum privacy
during the time the participant completed the questionnaires and blood was collected. To
ensure anonymity, each participant was assigned an identification number and all
instruments and specimens were labeled accordingly. A master list with participants’
names and codes was created. Access to the master list of participants’ names and
codes was restricted to the Principal Investigator, project coordinator, and research
48
nurse. The master list was kept in a locked cabinet separate from the data collected. All
information collected was independent from their prenatal care visit.
Balancing Benefits and Risks of a Study. According to IRB policies, optimizing
benefits and minimizing risks is important in all research studies. The information gained
from the parent study advanced the state of the science related to the etiology of
preterm labor. There were no direct benefits for participants taking part in the parent
study. Potential risks for the parent study included fatigue from participating in at least
105 minutes of data collection, emotional stress from answering personal questions, and
pain and bruising during and after blood collection. Risks were addressed as follows:
1. Participants were encouraged and given the opportunity to take breaks during
the data collection.
2. Participants who scored high on the depression scale were referred for
counseling.
3. Blood collection was performed by an experienced research nurse using a
small gauge needle.
No additional risks were anticipated for the current study. The parent study
received full IRB approval and after IRB approval submission for the current study, the
Office of Research Support (ORS) at the University of Texas at Austin determined that
this secondary analysis was excempt from further IRB requirements. Please refer to
Appendix B for the letter from ORS.
Measures
Research measures used to operationalize the concepts of interest have a vital
role in research projects (Polit & Tatano Beck, 2008). They are used to collect the data
needed to answer the research questions. Research instruments should be reliable and
49
valid. The self-report instruments used in this study included: the Multidimensional
Acculturative Stress Inventory (MASI) and the Multidimensional Acculturation Scale II
(MAS II).
Multidimensional Acculturative Stress Inventory (MASI). The MASI is a 36-
item instrument that measures the level of stress related to Spanish and English
competency pressures and pressures for and against acculturation (Rodriguez, Myers,
Bingham Mira, Flores, & Garcia-Hernandez, 2002). Level of stress is rated on 6-point
Likert-type scale with item responses ranging from (0) does not apply, (1) not at all
stressful to (5) extremely stressful. The measure generates four subscales, Spanish
Competency Pressure, English Competency Pressure, Pressure to Acculturate, and
Pressure Against Acculturation. Items from each of the subscales are averaged to obtain
a stress rating for each of the subscales. The reported reliabilities (Cronbach’s α) for
each of the subscales ranged from .77–.93 (Rodriguez et al., 2002). The validity for this
instrument was demonstrated using a factor analysis where the four factors explained
64.4% of the variance and were significantly correlated in the appropriate directions with
the selected criterion measures of acculturation, such as generational status and length
of U.S. residence (Rodriguez et al., 2002). This instrument was tested on 174 Mexican
origin adults aged 18–69 (M = 31.59, SD = 11.02), including 117 women who resided in
the Los Angeles, California, greater metropolitan area. Internal consistency reliability
(Cronbach’s α) for each subscale in this sample ranged from .79–.95. The Pearson r
correlations for the subscales ranged from .29–.50. See Appendix A for the detailed
survey.
Multidimensional Acculturation Scale II (MAS II). The MAS II is a 22-item
instrument used to assess acculturation by identifying Anglo American or Mexican
50
American involvement and identification in each culture and English and Spanish
language proficiency. Item responses in the MAS II are rated on a 6-point Likert-type
scale ranging from (0) does not apply and (1) not well/not at all/can’t speak or
understand to (5) very well/very much/very fluent. These subscales identify the
participant’s cultural identity as either Anglo or Mexican American with language
preference English or Spanish language. Items from the English proficiency and the
Anglo American identification subscales are summed and averaged to create an
American identity mean score. Items from the Spanish language proficiency and the
Mexican American identification subscales are summed and averaged to create a
Mexican identity mean score. The instrument has a reported reliability (Cronbach’s α) of
.96 for the language proficiency subscales and .90 for the ethnic identity subscale
(Rodriguez, Bingham Mira, Paez, & Myers, 2007). Validity of this instrument was
demonstrated with correlations of commonly accepted acculturation indicators of
generational status and length of U.S. residence. First generation included participants
born in Mexico, second generation included participant’s mother having been born in
Mexico and the participant having been born in the U.S., third generation included
participant’s grandmother having been born in Mexico and participant and mother having
been born in U.S., fourth generation included participant’s great-grandmother having
been born in Mexico and the participant and participant’s mother and grandmother being
born in U.S. As expected, generational status was significantly correlated with the
English language proficiency (r = .56, p < .01), Spanish language proficiency (r = - .74, p
< .01), and Anglo identity (r = .32, p < .01) subscales. Also as expected, length of U.S.
residency was significantly correlated with the English language proficiency (r = .73, p <
.01), Spanish language proficiency (r = - .63, p < .01), and Anglo identity (r = .42, p <
51
.01) subscales. Neither indicator was significantly correlated with the Mexican cultural
identity subscale (r = -.07, p >.05; r = -.03, p > .05). This instrument was tested on 248
adults aged 18–69 of Mexican origin (M = 36.44, SD = 11.93), including 124 women
from the Los Angeles greater metropolitan area. Internal consistency reliability
(Cronbach’s α) for each subscale in this sample ranged from .80–.96. The Pearson r
correlations for the subscales ranged from -.08–.52.
Leptin. Leptin was defined as a pleiotropic hormone that plays a role in
regulating energy homeostasis, appetite regulation, fat disposition, and metabolic and
fertility processes (Otero et al., 2006; Bouloumie et al., 2007). Leptin was
operationalized by enzyme linked immunosorbent assay. Assay plates were purchased
from the American Laboratory Products Company, Salem, New Hampshire (ALPCO),
and the ELISA procedure was followed according to manufacturer’s specifications.
ELISA is a biochemical technique used to measure protein levels (Vedhara & Irwin,
2005). The ELISA test kit was purchased from ALPCO reports leptin mean detectible
dose (MDD) with a range of .020 –.128 ng/ml with sensitivity of 0.057 based on leptin
standard curves (ALPCO, 2005). Mean detection dose and sensitivity is comparable to
other kits on the market (Neogen, 2012). Mean detection dose and sensitivity for ALPCO
kit was determined by the National Committee on Clinic Laboratory Standards
(NCCCLS) protocol and inter-assay (between assays) and intra-assay (within assays)
precisions were verified and comparable to other kits on the market (ALPCO, 2012).
ALPCO (2012) reported leptin levels for lean women of 7.4 ng/mL. Leptin levels are
directly proportional to BMI and are higher in pregnancy ranging from 117.4–163.8
ng/mL with the highest levels seen during the second trimester (Hardie, Trayhurn,
52
Abramobvich, & Fowler, 1997). Higher levels of leptin are attributed to the weight and
hormonal changes for pregnancy (Hardie, Trayhurn, Abramobvich, & Fowler, 1997).
Adiponectin. Adiponectin was defined as a polypeptide hormone produced in
adipose tissue that has anti-inflammatory, anti-atherogenic, and insulin sensitizing
properties. Adiponectin was operationalized by enzyme linked immunosorbent assay.
The ELISA test kit was purchased from ALPCO reports adiponectin MDD range of .075–
4.8 ng/mL and sensitivity of 0.019 ng/mL based on adiponectin standard curve and
strong correlations (r = .99) when compared to other commercial kits (ALPCO, 2013).
Data Collection
Survey Data. During the data collection visit, the research nurse collected vital
signs (i.e., blood pressure, pulse, temperature), weight, calculated gestational age, and
administered the pen and pencil questionnaires. The participants filled out a
demographic information sheet and completed the questionnaires. Questionnaires and
demographic data sheets were all kept in a secured cabinet in the research offices. The
estimated time for the pen and paper questionnaires was 90 minutes. The nurse then
collected the blood sample from the participant. The order of the protocol was
implemented to help the participant become familiar with the study environment and help
decrease stress prior to blood collection.
Physiologic Data. Peripheral venous blood was drawn from the antecubital area
using a butterfly vacutainer needle into a syringe by the research nurse. This was done
between 1 p.m. and 3 p.m. to help control for the diurnal patterns of certain markers.
Participants were instructed not to eat two hours prior to data collection to control for the
effects of eating or fasting on the markers under study. The research nurse verified their
last dietary intake was within the instructed time. The estimated time for physiologic data
53
collection was 15 minutes. The 30 mL of blood collected were centrifuged; the plasma
was transferred into smaller aliquots, frozen, and stored in a secured, temperature
controlled freezer at -80°C in the biobehavioral laboratory at the University of Texas at
Austin until the blood was ready for the assays.
Data Analysis
Data analysis was conducted using the Statistical Package for the Social
Sciences (SPSS) Version 19 (IBM, 2011). Responses for the MAS II and MASI surveys
were electronically entered into spreadsheet format and exported into SPSS. The
existing laboratory values from the parent study were entered by the research nurse into
the database after the laboratory technician completed the laboratory procedures. All
data were manually verified for accuracy. Laboratory data for this study were entered
and verified in the same manner. The database for the parent study was filtered and all
participants who had GDM were extracted. The 38 participants with diagnosed GDM
from the parent study were manually matched according to age and BMI with
participants from the parent study who did not develop GDM, and a new SPSS database
was created and used for data analysis.
Physiologic Data
Leptin and adiponectin were quantified by enzyme linked immunosorbent assay
(ELISA). ELISA is a biochemical technique used to measure protein levels (Vedhara &
Irwin, 2005). The assays consisted of an adipokine-specific monoclonal antibody that
detects the presence and level of the adipokine of interest.
All data were verified for accuracy. Frequency tables were generated for all
variables. Descriptive, parametric, and and correlation statistics were used to analyze
the data (Polit & Tatano Beck, 2008). Data analysis was conducted systematically and
54
verified data that it met the pertinent assumptions related to the statistical tests of
interest. Descriptive statistics are used to describe and summarize data (Polit & Tatano
Beck). They enable researchers to summarize the characteristics of the sample.
Descriptive statistics generated for the subsample included the mean, standard
deviation, and frequencies. Correlational statistics explored relationships between
variables. Independent t-tests were conducted to analyze differences between two
means.
The research questions reflective of their specific aims and planned analyses
were as follows:
Specific Aim #1: To explore relationships between the psychosocial stressors
(i.e., acculturation and acculturative stress) and metabolic markers (i.e., leptin and
adiponectin) in Mexican American women with and without gestational diabetes.
Research Question 1. Is there a significant relationship between levels of the
psychosocial markers of acculturation and acculturative stress and the metabolic
markers of leptin and adiponectin? Planned analysis: Pearson r Correlation
Specific Aim #2: To examine differences in the metabolic markers of leptin and
adiponectin in Mexican American women with and without gestational diabetes.
Research Question 2.1. Is there a significant difference in the levels of the
psychosocial markers of acculturation and acculturative stress between women
with and without gestational diabetes? Planned Analysis: Independent samples
t-test.
Research Question 2.2. Is there a significant difference in the metabolic
markers of leptin and adiponectin between women with and without gestational
diabetes? Planned Analysis: Independent samples t-test.
55
Threats to Design Validity
Statistical Validity
Statistical validity relates to the study results and represents the true differences
belong to the study design and not those that occur as a result of random error (Brink &
Wood, 2001). The MAS II and MASI have established reliability over time. This study is
limited to data that was already collected in the parent study; additional instrumentation
was not used. In this secondary analysis, statistical power is limited due to the small
sample size. Because the sampling techniques used in this study were non-probability,
possible error introduced during sampling cannot be measured, thus limiting the validity
of the results. To address this threat, systematic and consistent data collection methods
were used by the parent study for questionnaire administration and blood specimen
collection and storage.
Physiologic data results for the biomarkers were dependent on proper storage
and handling of the stored blood as well as time elapsed since collection. Strict
temperature controls were maintained for the freezers at all times, and the assays were
completed in batches of 50 as soon as information was collected from 50 participants.
Statistical and normal distribution assumptions were addressed.
Internal Validity
Internal validity is the degree that the study’s results are attributed to the
research design and not to systematic error (Polit & Tatano Beck, 2008). Internal validity
was controlled by reducing testing effect by using the shortest valid instruments to
measure the concepts of interest, thus reducing the burden on the participant.
Participants were given detailed instructions on the questionnaires to ensure
questionnaires were appropriately completed. The research nurse was available to
56
answer all questions during data collection and reviewed each questionnaire to ensure
completion.
Construct Validity
Construct validity is the degree to which inferences can be made that the
instruments used in the study appropriately measure the theoretical concepts of the
study (Brink & Wood, 2001). The instruments were validated by using two commonly
used indicators of acculturation: generational level and length of U.S. residency. Both
instruments demonstrated significant correlations indicating construct validity.
External Validity
External validity is the degree to which the study’s results can be generalized to a
sample outside the one studied (Polit & Tatano Beck, 2008). The findings in this study
may not be generalizable to all Mexican Americans residing in the United States but will
be applicable to those residing in Central Texas who have characteristics similar to the
sample.
Summary
This chapter addressed the research approach and methodology used in this
study. Institutional review board approval, research design, sampling and recruitment
procedures, and informed consent were discussed. Procedures for data collection and
analysis and interpretation of results were described. Finally, potential threats to validity
were acknowledged and addressed.
57
CHAPTER IV
RESULTS
This chapter presents the results of this secondary study by answering the
research questions posed in Chapter I using the statistical methods outlined in Chapter
III. The sample is described by reporting frequency distributions of demographic data.
Then, frequency distributions of scores for survey instruments and values for laboratory
tests are presented. The research questions were answered through performing
parametric tests, specifically calculating Pearson r correlations and conducting
independent sample t-tests.
Description of Sample
Frequencies were calculated to provide a description of the sample. These
included the following demographic characteristics: country of birth, language
preference, generational level, marital status, regional background, educational level,
income, age, and years of residence in the United States. Description of the biological
variables include height, weight, pre-pregnancy weight and BMI, systolic blood pressure,
leptin and adiponectin levels, and leptin-adiponectin ratio.
Demographic Characteristics
The sample consisted of a total of 76 Mexican American women, 38 with GDM
and 38 healthy controls without GDM. Individual and biologic characteristics are reported
by group. The groups were overall very similar.
Gestational Diabetes Group. The age range for the GDM group was 21–42
years (M = 29.79, SD = 5.62); these women had a reported range of U.S. residence of
8–39 years (M = 23.42, SD = 8.15). Approximately, 55% of the group had been born in
the U.S., and 46% were born in Mexico. A total of 71% reported having a preference for
58
the English language, while 29% reported having a Spanish language preference.
Frequencies and percent for generational level, marital status, regional background,
education, and income are reported in Table 4.1.
Healthy Control Group (Non-Gestational Diabetes). The age range for the
healthy control (non-GDM) group was aged 21–43 years (M = 29.82, SD = 5.68); these
women had a reported range of U.S. residency of 7–39 years (M = 23.11, SD = 8.35). A
total of 61% of the group had been born in the U.S., and 39% were born in Mexico.
Frequencies and percent for generational level, marital status, regional background,
education, and income are reported in Table 4.1.
59
Table 4.1
Demographic Characteristics of Women with and without Gestational Diabetes
Demographic
Characteristic
GDM Group Healthy Control (Non GDM)
Group
n % Range M SD n % Range M SD
Country of birth
U.S. 21 55 23 61
Mexico 17 45 15 39
Language preference
English 27 71 25 66
Spanish 11 29 12 32
Generational level
1st 14 37 20 53
2nd
16 42 3 8
3rd
2 5 5 12
4th 5 13 9 24
Marital status
Married 22 58 23 60
Single 16 42 15 40
Regional background
Houston, TX 13 34 17 44
Pasadena, TX 18 47 14 36
Galveston, TX 2 5 0 0
Austin, TX 5 13 7 18
Education (years)
< 12 14 37 6 15
12 9 24 16 42
13-15 9 24 8 21
≥ 16 2 5 3 8
Income
< $11,999 5 13 5 13
$12,000–$24,999 10 26 6 16
$25,000–$49,999 14 37 14 37
≥ $50,000 3 8 6 16
Age (years) 38 100 21–42 29.79 5.62 38 100 21–43 29.82 5.68
Years U.S. Residence 38 100 8–39 23.42 8.15 38 100 7–39 23.11 8.35
60
Biologic Characteristics
Biologic characteristics examined for this study included height, weight, pre-
pregnancy weight and BMI, leptin, adiponectin, and leptin-adiponectin ratio. For the
GDM group, these women’s measured height ranged from 58–69 inches (M = 62.82, SD
= 2.58) and their weight ranged from 123–276 pounds (M = 196.76, SD = 39.11).
Reported pre-pregnancy weight ranged from 97– 288 pounds (M = 183.16, SD = 46.23)
and their calculated pre-pregnancy BMI ranged from 18.02–55.65 (M = 32.65, SD =
8.27). ELISSA quantified leptin levels ranged from 21.94–355.58 ng/mL (M = 92.82, SD
= 78.99) and adiponectin levels ranged from 2.08–10.38 ng/mL (M = 6.20, SD = 1.96).
The mean for the calculated leptin-adiponectin ratio for the GDM group was 16.88 (SD =
14.76).
For the healthy control (non-GDM) group, their measured height ranged from 55–
67 inches (M = 62.32, SD = 2.55), and their weight ranged from 108–295 pounds (M =
194.75, SD = 43.25). Reported pre-pregnancy weight ranged from 93–285 pounds (M =
180.32, SD = 43.25) and the calculated pre-pregnancy BMI ranged from 19.39–55.65 (M
= 32.58, SD = 7.68). ELISSA quantified leptin levels ranged from 7.66–309 ng/mL (M =
108.75, SD = 72.77) and adiponectin levels ranged from 0.21–14.97 ng/mL (M = 6.81,
SD = 2.82). The mean for the calculated leptin-adiponectin ratio for the Non-GDM group
was 31.49 (SD = 85.94). Biologic characteristics for each group are presented in Table
4.2.
61
Table 4.2
Biologic Characteristics of Women with and without Gestational Diabetes
Biologic Characteristic
GDM Group Healthy Control (Non GDM) Group
n % Range M SD n % Range M SD
Height (inches) 38 100 58–69 62.82 2.58 38 100 55–67 62.32 2.55
Weight (pounds) 38 100 123–276 196.76 39.11 38 100 108–295 194.75 43.25
Pre-pregnancy weight 38 100 97–288 183.16 46.23 38 100 93–285 180.32 43.25
Pre-pregnancy BMI 38 100 18.02–55.65 32.65 8.27 38 100 19.39–55.65 32.58 7.68
BMI < 20 3 8 1 3
BMI 20-24.9 3 8 5 13
BMI 25-29.9 9 24 10 26
BMI > 30 23 60 22 58
Leptin 38 100 21.94–355.58 92.82 78.99 37 97 7.66–309.00 108.75 72.77
Adiponectin 38 100 2.08–10.38 6.20 1.96 38 100 0.21–14.97 6.81 2.82
Leptin-adiponectin ratio 38 100 2.59–70.27 16.88 14.76 38 100 0.53–539.76 31.49 85.94
Note. Overall leptin levels ranged from 21.94 to 355.58 and were all included in data analysis. Levels were verified with laboratory and there were no indicators the results were flawed. When excluding high levels of leptin, no significant differences were observed; therefore, due to small sample size all levels were included. Adiponectin levels ranged from 0.21 to 14.97. Levels were verified with laboratory. Laboratory notes indicated one sample may have contained an interfering substance resulting in close to undetectable levels. This value was replaced by the corresponding subgroup’s mean value for adiponectin. When excluding the replaced value, no significant results were observed.
62
Measures
The survey instruments used in this study to measure acculturative stress and
acculturation were the self-report instruments: Multidimensional Acculturation Scale II
(MAS II) and the Multidimensional Acculturative Stress Inventory (MASI). ELISSA
technique from ALPCO was used to quantify leptin and adiponectin.
Multidimensional Acculturation Scale II (MAS II). The MAS II is a 22-item self-
report survey consisting of four subscales used to measure acculturation. Frequencies
and scores for each subscale are provided in Table 4.3.
Multidimensional Acculturative Stress Inventory (MASI). The MASI is a 36-
item self-report survey consisting of four subscales used to measure acculturative
stress. Frequencies and scores for each of the subscales are provided in Table 4.3.
63
Table 4.3
Subscale Survey Scores
Survey Scale
Gestational Diabetes Non Gestational Diabetes
n Range M SD n Range M SD
Multidimensional Acculturation Scale II (N = 22)
Subscale
English proficiency 6 0–30 24.81 7.59 6 0–30 24.25 7.93
Spanish proficiency 5 3–25 19.49 7.11 5 1–25 19.08 6.68
American culture identity 5 12-25 19.89 3.65 5 5–25 18.76 5.07
Mexican culture identity 6 13–30 25.62 4.27 6 12–30 23.71 5.14
Multidimensional Acculturative Stress Scale (N = 36)
English competency pressure 8 0–40 5.05 9.06 8 0–19 3.74 4.97
Spanish competency pressure 8 0–17 4.42 5.40 8 0–17 3.92 4.80
Pressure to acculturate 11 0–29 5.95 6.45 11 0–23 5.34 5.52
Pressure against acculturation 9 0–15 4.43 4.40 9 0–17 3.68 4.13
Note. N = number of total survey questions, n = number of survey questions per subscale
64
Leptin. Leptin was defined as a pleiotropic hormone that plays a role in
regulating energy homeostasis, appetite regulation, fat disposition, metabolic and fertility
processes (Otero et al., 2006; Bouloumie, Curat, Miranville, & Sengenes, 2007). ELISA
is a biochemical technique used to measure protein levels (Vedhara & Irwin, 2005).
ALPCO reports a leptin mean detectible dose of (MDD) 0.50 ng/mL with a sensitivity of
0.42. Mean reported leptin levels in lean women were 7.4 ng/mL (ALPCO, 2010). Leptin
levels for the GDM group ranged from 21.94–355.58. The mean measured leptin for the
GDM group was 92.82 (SD = 78.99). Leptin levels for the healthy controls (non GDM)
group ranged from 7.66–309.00 with the mean measured leptin of 108.75 (SD = 72.77).
Levels were verified with laboratory and there were no indicators the results were
flawed. When excluding high levels of leptin during data analysis, no significant
differences were observed when excluding and including the high levels; therefore, due
to small sample size all levels were included for the final analysis.
Adiponectin. Adiponectin was defined as a polypeptide hormone produced in
adipose tissue that has anti-inflammatory, anti-atherogenic and insulin sensitizing
properties. Adiponectin was operationalized by enzyme linked immunosorbent assay.
Adiponectin levels for the GDM group ranged from 2.08–10.38 with a mean adiponectin
level 6.20 (SD = 1.96). Adiponectin levels for the healthy control (non-GDM) group
ranged from 0.21–14.97 with a mean adiponectin of 6.81 (SD = 2.82). Serum
adiponectin range for this study is consistent with other studies that have reported
adiponectin ranges from 2–20 (Lihn, Pederson, & Richelsen, 2005). Adiponectin levels
were verified with laboratory. Laboratory notes indicated one sample from the non-GDM
group possibly contained an interfering substance resulting in close to undetectable
65
levels. This value was replaced with the non-GDM group’s mean value for adiponectin.
When excluding the replaced value, no differences were observed.
Research Questions
This section answers the research questions posed in Chapter I. The research
questions were formulated to address the major purposes of this study which were to
explore relationships between the psychosocial stressors of acculturation and
acculturative stress in Mexican American women with and without gestational diabetes,
and to examine whether differences exist in the metabolic markers of leptin and
adiponectin in Mexican American women with and without gestational diabetes. Survey
instruments were used to measure the psychosocial markers of acculturation and
acculturative stress. The ELISA technique was used to measure the metabolic markers
of leptin and adiponectin.
Research Question 1
Is there a relationship between levels of the psychosocial markers of
acculturation (i.e., English proficiency, Spanish proficiency, American cultural identity,
Mexican cultural identity) and acculturative stress (i.e., English competency pressure,
Spanish competency pressure, pressure to acculturate, pressure against acculturation),
and the metabolic markers of leptin and adiponectin?
MAS II
Pearson r correlations were used to answer this question. Findings are reported
for each of the subscales of acculturation in addition to the common indicators of
acculturation (i.e., preferred language, residency index).
English proficiency. There was a statistically significant, positive correlation
found between English proficiency and weight (r = .27, p < .01) and leptin level (r = .26,
66
p < .05). There was a statistically significant, negative correlation between English
proficiency and residency index (r = -.83, p < .01); preferred language (r = -.69, p < .01),
No statistically significant correlations were found between English proficiency
and the following variables:
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
newborn weight
adiponectin
leptin/adiponectin ratio
Spanish proficiency. There was a statistically significant, positive correlation
found between Spanish proficiency and residency index (r = .45, p < .01) and preferred
language (r = .31, p < .01).
No statistically significant correlations were found between Spanish language
proficiency and the following variables
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
newborn weight
American culture identity. There was a statistically significant, positive
correlation between American culture identity and leptin (r = .27, p < .05) There was a
statistically significant, negative correlation between American culture identity and
resident index (r = -.47, p < .01), preferred language (r = -.48, p < 01).
67
No statistically significant correlations were found between American cultural
identity and the following variables:
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
newborn weight.
Mexican culture identity. There was a statistically significant, positive
correlation found between Mexican cultural identity and newborn weight (r = .26, p <
.05). There was a statistically significant, negative correlation found between English
proficiency and preferred language (r = -.23, p < .01).
No statistically significant correlations were found between Mexican cultural
identity and the following:
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
residency index
leptin
adiponectin
leptin/adiponectin ratio
BMI group
MASI
68
Pearson r correlations were used to answer this question. Findings are reported
for each of the subscales for acculturative stress.
English competency pressure. There was a statistically significant, positive
correlation between English competency pressure and residency index (r = .61, p < .01)
and preferred language (r = .47, p < .01).
No statistically significant correlations were found between English language
competency pressure and
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
newborn weight
leptin
adiponectin
leptin/adiponectin ratio
BMI group
Spanish language competency pressure. No statistically significant
correlations were found between Spanish language competency pressure and
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
newborn weight
resident index
69
preferred language
leptin
adiponectin
leptin/adiponectin ratio
BMI group
Pressure to acculturate. No statistically significant correlations were found
between pressure to acculturate and
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
newborn weight
residency index
preferred language
leptin
adiponectin
leptin/adiponectin ratio
BMI group
Pressure against acculturation. No statistically significant correlations were
found between pressure against acculturation and
gestational diabetes
pre-pregnancy weight
pre-pregnancy BMI
weight
70
newborn weight
resident index
preferred language
leptin
adiponectin
leptin/adiponectin ratio
BMI group
Values for the Pearson r correlation coefficients are presented in Tables 4.4a
and 4.4b.
71
Table 4.4a
Correlations among Study Variables
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1. Gestational diabetes — .03 -.01 .03 .13 -.02 -.08 .04 -.21 .08 .01 -.10 .11 -.15 -.02
2. Pre-pregnancy weight — .84** .93** .14 -.26* -.35** .20 -.02 .19 .16 -.16 .02 -.09 -.01
3. Pre-pregnancy BMI — .84** .05 -.27* -.31** .14 -.04 .12 .06 -.13 .05 -.04 .02
4. Weight — .21 -.35** -.36** .27** -.11 .21 .17 -.20 .07 -.11 .01
5 Newborn weight — .06 .02 .04 .09 .14 .26* -.02 -.19 -.05 -.17
6 Resident index — .81** -.83** .45** -.47** -.12 .61** -17 .15 .01
7 Preferred language — -.69** .31** -.48** -.23** .47** -.12 .06 -.04
Multidimensional Acculturation Scale II
8 English proficiency — -.29* .50** .22 -.58** .05 -.08 -.04
9 Spanish proficiency — .08 .33** .24* -.63** .05 -.22
10 American culture identity — .52** -.22 -.03 -.04 -.05
11 Mexican culture identity — -.11 -.38 -.03 -.21
Multidimensional Acculturative Stress Inventory
12 English competency pressure — -.04 -.59** .33**
13 Spanish competency pressure — .23 .59**
14 Pressure to acculturation — .74**
15 Pressure against acculturation —
** p < 0.01. * p < 0.05.
72
Table 4.4b
Correlations among Study Variables
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 Leptin — -.10 .89** .-10 .52** .45** .38** .26* -.02 .27* .16 -.18 .01 .02 .53
2 Adiponectin — -.38** -.17 -.23 -.27* -.26* -.06 .04 -.11 .05 -.01 .09 -.09 -.11
3 Leptin-adiponectin ratio — -.12 .53** .50** .39** .22 -.10 .16 .13 -.18 -.06 .05 .09
4 Gestational diabetes — .03 .03 -.02 .04 .03 .13 .20 .09 .05 .05 .09
5 Weight — .93** .71** .27** -.11 .21 .17 -.20 .07 -.11 .01
6 Pre-pregnancy weight — .79** .20 -.02 .19 .16 -.16 .02 -.09 -.01
7 BMI group — .04 -.21 .08 .01 -.10 .11 -.15 -.02
Multidimensional Acculturation Scale II
8 English proficiency — -.29* .50** .22 -.58** .05 -.08 -.04
9 Spanish proficiency — -.08 .33** .24* -.63** .05 -.22
10 American culture identity — .52** -.22 -.03 -.04 -.05
11 Mexican culture identity — -.11 -.38 -.03 -.21
Multidimensional Acculturative Stress Inventory
12 English competency pressure — -.04 .59** .33**
13 Spanish competency pressure — .23 .59**
14 Pressure to acculturation — .74**
15 Pressure against acculturation —
** p < 0.01. * p < 0.05
73
Research Question 2.1.
Is there a significant difference in the levels of the psychosocial markers of
acculturation and acculturative stress between women with and without gestational
diabetes?
Independent t-tests were used to answer this question. These revealed that there
was no significant difference between women with and without gestational diabetes in
the levels of the psychosocial markers of acculturation (English language proficiency,
Spanish language proficiency, American cultural identity, Mexican cultural identity) and
acculturative stress (English language competency pressure, Spanish language
competency pressure, pressure to acculturate, and pressure against acculturation). T-
test results are presented in Table 4.5.
Research Questions 2.2.
Is there a significant difference in the metabolic markers of leptin and adiponectin
between women with and without gestational diabetes?
Independent t-tests were used to answer this question. These revealed that there
was no significant difference between women with and without gestational diabetes in
the levels of the metabolic markers of leptin, adiponectin, and in the leptin/adiponectin
ratio. T-test results are presented in Table 4.5.
74
Table 4.5
Independent t-test Analysis of Difference between Women with and without Gestational Diabetes
Gestational Diabetes (n = 38)
Non-Gestational Diabetes (n = 38)
M
SD M SD t df p
Pre-pregnancy weight 183.16 46.23 180.32 43.95 -.28 74 .78
Pre-pregnancy BMI 32.65 8.27 32.58 7.68 -.04 74 .97
Leptin 93.82 78.99 108.75 72.77 .86 74 .39
Adiponectin 6.20 1.96 6.98 2.60 1.47 74 .15
Leptin-adiponectin ratio 18.88 14.76 17.74 14.63 .26 74 .80
Multidimensional Acculturation Scale II
English proficiency 24.81 7.59 24.25 7.93 -.31 73 .76
Spanish proficiency 19.49 7.11 19.08 6.68 -.26 73 .80
American cultural identity 19.89 3.65 18.76 5.07 -1.10 73 .27
Mexican cultural identity 25.62 4.27 23.71 5.14 -1.75 73 .09
Multidimensional Acculturative Stress Inventory
English competency pressure 5.05 9.06 3.74 4.97 -.78 73 .44
Spanish competency pressure 4.42 5.40 3.92 4.80 -.42 73 .67
Pressure to acculturate 5.95 6.45 5.34 5.52 -.44 73 .66
Pressure against acculturation 4.43 4.40 3.68 4.13 --.76 73 .45
75
Summary
The results from this study answered the research questions posed and indicated
that significant relationships do exist between some of the variables of interest; however,
there were no overall significant differences found between women with and without
gestational diabetes. These mixed results may be an indicator of a need to further
explore these concepts.
This chapter presented the results of this study by answering the research
questions posed in Chapter I using statistical methods outlined in Chapter III. The
sample was described by reporting frequency distributions of demographic data. Then,
frequency distributions of scores for survey instruments and values for laboratory tests
were provided. Parametric tests including Pearson r correlations and t-tests were used
to answer the research questions.
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CHAPTER V
DISCUSSION AND SUMMARY
This chapter begins by reviewing the purpose and research questions presented
in Chapter 1 before interpreting the findings presented in Chapter 4. Study limitations are
presented and addressed. Applications to theory development, implications to nursing
practice, and recommendations for future research are considered.
This biobehavioral study was a secondary analysis of the NIH-funded study,
Preterm Birth: Psychoneuroimmunology in Hispanics. This study explored relationships
between the psychosocial stressors of acculturation and acculturative stress in Mexican
American women with and without gestational diabetes and examined whether
differences exist in the metabolic markers of leptin and adiponectin in Mexican American
women with and without gestational diabetes.
Interpretation of Findings
Findings in this study were mixed. Small to moderate significant correlations
were found between some of the psychosocial variables and physiological variables, but
overall there were no significant relationships between the psychosocial variables
(acculturation and acculturative stress), metabolic variables (leptin and adiponectin), and
gestational diabetes or differences in women with and without gestational diabetes.
Psychosocial Stress
Acculturation is a multi-factorial and dynamic process that has been linked to
high risk of obesity (Oza-Frank & Cunningham, 2010). The findings support the current
literature (Oza-Frank & Cunningham, 2010; Perez-Escamilla & Putnik, 2007) and
indicate a positive relationship between acculturation and body weight among this group
of Mexican American women. Findings indicated that the longer women reside in the
77
U.S. and the more acculturated they report becoming, the heavier their weight. Existing
research attributes overweight and obesity among first generation Americans to the
demands of the transition into the American mainstream culture including the stress
associated with departure from their country of origin, social isolation, language
difficulties, financial difficulties and discrimination (Akresh, 2007). Dietary and physical
activity patterns which contribute to the changes in weight are also thought to change as
individuals adapt to their new culture (Akresh, 2007). The new dietary patterns of high
fat, high sugar diet, along with more sedentary physical activity patterns eventually get
transferred to the next generation, making successive generations more vulnerable to
overweight and obesity.
In contrast, acculturative stress was not significantly associated with weight or
gestational diabetes. However, research indicates that acculturative stress is a powerful
concept that has been associated with negative effects on individuals including poor
psychological functioning, depression, and anxiety (Torres, Driscoll, & Voell, 2012;
Iturbide, Raffaelli, & Carlo, 2009). As a chronic stressor, acculturative stress can be a
direct result of the acculturation process. During the process of acculturation, individuals
can adapt to the host culture using different strategies including integration, assimilation,
separation or marginalization. Separation and marginalization are considered the most
challenging and can place individuals for higher risk for acculturative stress (Berry &
Sam, 1997). Acculturative stress is highly dependent on an individual’s appraisal of the
acculturation experience itself. Individuals must choose what characteristics they want to
keep from their own culture and what they want to adopt from the host culture (Caplan,
2007; Berry & Sam, 1997). Acculturative stress models depict the concept on a
continuum where individuals can select to keep characteristics of their country of origin,
78
to identify more closely with the host society, or do both making the concept difficult to
investigate (Berry & Sam, 1997).
Equally challenging to investigate and related to stress, this study proposed
allostatic load as a potential contributor to altered metabolic response. Unfortunately,
without a solid relationship with acculturative stress, one of the major markers of stress
in this study, further investigation is needed to examine this study’s proposed
relationship of the body reaching allostatic load as a result of the changes of the
acculturation process, mostly influenced by acculturative stress. Allostatic load is difficult
to examine in pregnant women because some of its markers, such as cholesterol and
waist hip ratio, cannot adequately be measured during pregnancy. Future longitudinal
studies could further pursue this hypothesis by including more clearly defined and
measurable allostatic load markers such as cortisol, norepinephrine, epinephrine,
dehydroepiandrosterone (DHEA), cholesterol, waist hip ratio, glycosylated hemoglobin,
and blood pressure in women during the pre-conception period, throughout the
pregnancy, and then postpartum (Geronimus, Hicken, Keene, & Bound, 2006; Seeman,
McEwen, Rowe, & Singer, 2001). Examination of markers such as cholesterol and waist
hip ratio would be limited to the pre-pregnancy and postpartum periods. Having allostatic
load information for the pre-conception period, different pregnancy trimesters, and
postpartum periods would provide valuable information on biological risks associated
with the process of acculturation and acculturative stress in relation to allostatic load
markers.
Metabolic Response
The study of adipokines in metabolic response is an emerging science that is
actively establishing a credible body of evidence supporting the role of adipokines in
79
disease, and implicating leptin and adiponectin in altered metabolic responses (Kyrou &
Tsigos, 2009). This study supports prior findings that suggest that leptin levels are
associated with weight. Generally, overweight and obese individuals have overall higher
levels of leptin and other pro-inflammatory compounds, which place them at risk for
altered metabolic responses—specifically metabolic syndrome, cardiovascular disease,
and diabetes (Kyrou & Tsigos, 2009). Our data describes a significant, positive direct
relationship between weight and leptin levels, which supports prior findings.
Although the science of the physiology of the metabolic response is still evolving,
little is known about how psychosocial factors influence these responses. Few research
studies have investigated the impact of how the transition of adapting to U.S.
mainstream culture affects levels of leptin and other physiologic responses. This study
further examined the relationship of leptin with the psychosocial influences of
acculturation and acculturative stress. The study contributes a novel and important
finding by finding a significant association between English proficiency and American
culture identity and levels of leptin. This small but significant finding supports the need to
expand the science on the biological influences of acculturation and the need for
culturally sensitive care that begins with assessing modifiable risk factors and providing
appropriate interventions to ease the transition of individuals adapting to the American
culture.
By identifying modifiable risk factors associated with the acculturation process,
such as social isolation, depression, and anxiety, advanced practice nurses can
implement cognitive behavioral interventions designed to alleviate these symptoms.
Additionally, implementing weight loss and exercise programs for weight management
80
can help alleviate the risk of weight gain, which has been found among first generation
Americans adjusting to the American culture.
Gestational Diabetes Mellitus
A surprising finding of this study was a lack of significant relationships and
differences in women with and without gestational diabetes related to weight and levels
of leptin and adiponectin. Overweight and obesity are established risk factors for
gestational diabetes and other metabolic alterations (Yogev & Visser, 2009). While
previous studies have supported strong associations between gestational diabetes and
weight, this finding was not demonstrated in this sample. It is possible that this
association was not clearly delineated because the sample was matched by weight.
Because of this approach, there was not enough variability in the women’s weight that
would allow us to determine any differences. Perhaps a random selection technique for
the non GDM group would have provided more diversity in weight ranges making
differences more evident. Similarly, the literature supports that there are differences in
leptin and adiponectin levels in women with and without gestational diabetes. However,
this study did not find any significant differences between the two groups (Ategbo 2006;
Winzer et al., 2004). Gestational diabetes has been implicated in pregnancy
complications that affect both the mother and baby. Because it is usually diagnosed
during the third trimester of pregnancy, it creates prolonged fetal exposure during
vulnerable periods of fetal development (Yogev & Visser, 2009). Prevention and early
recognition of glucose intolerance is vital in women of childbearing age at risk for
gestational diabetes to prevent prolonged fetal exposure. To help diagnose gestational
diabetes early, further research is needed to investigate what other markers may be
implicated in its development.
81
Limitations
This study met its aims and answered the research questions posed. However,
several limitations exist that restrict generalizability of the findings.
Self-Report
This study relied on self- report for demographic and survey data. Self-report
survey studies can be limiting due to the nature of the participants’ willingness to answer
questions truthfully and accurately since personal biases may exist. Additionally,
participants’ may not fully understand or fail to disclose lack of understanding of the
questions of interest making their responses inaccurate. Demographic data reported
country of birth and generational level did not match as expected. This could be
attributed to inconsistent participant self-report, personal introspective, and/or lack of
understanding of the question.
Sample size
The sample size in this study was small, which affected its power and overall
generalizability. A larger sample size with a broader range of women’s weight and more
equitable generational levels (i.e., greater participation of second generation participants
for the non-GDM group) could have provided more information, as well as an opportunity
to use more advanced statistical analyses to evaluate the complex relationships
investigated. Evidence supports that people in the transitional stages of acculturation,
such as those of the second generation, are more likely to be actively struggling with the
acculturation process and may develop worse health problems compared with earlier
and later generations (Perez-Escamilla & Putnik, 2007). In addition, because the
relationships among the concepts explored in this study are multifactorial, dynamic, and
complex, inclusion of mediators or moderators that may affect the psychosocial and
82
physiologic processes may be useful for explaining potential relationships among the
variables.
Matching techniques
Matching the women with and without gestational diabetes on weight was
limiting. Because weight is a major contributor to metabolic response, having a primarily
obese sample that was matched by weight, biological information was unavailable on
normal weight women. Matching on weight compromised the variability of the sample
and limited the findings by decreasing the data available on normal weight women.
Having a more diverse weight range in the women without gestational diabetes would
have provided useful information. Obesity, as a major contributor to metabolic response,
may also possibly have obscured other existing relationships. Recruiting more normal
weight women for both groups may have been a better technique to meet the goals of
this study. Furthermore, random selection of the non-GDM would have
Despite these limitations, the study’s findings revealed valuable information and
informed the science on gestational diabetes. Statistically significant, preliminary
Pearson r correlations were obtained, which warrant further exploration of the concepts
of interest.
Application to the Theory Development
Theory development in professional nursing is important for the growth of nursing
science. This study was influenced by Leininger’s theory of transcultural nursing (1978;
1985), which proposed that culturally sensitive care begins with recognizing that
individuals are the sum of their historical, cultural, and social influences. It also was
based on Neuman’s systems model (1982), which proposed that individuals seek to
maintain a balance in the interrelationships of stressors and environment in order to
83
achieve health. This study’s conceptual model also was guided by McEwen’s allostatic
load theory (1988), which specifies that the physiological cost of individuals’ adaptation
to stressors can lead to a decline of physiological function, resulting in allostatic load
which can increase risk of disease.
Consistent with Leininger’s and Neuman’s theories, this study’s findings of
significant associations between the psychosocial (i.e., resident index, preferred
language, English language proficiency, American cultural identity) and biological
(weight, leptin level) variables supports that cultural influences are associated with
physiological processes. This finding warrants further investigation of these dynamic and
complex relationships to advance the science. Specifically, investigating whether the
psychosocial variables (i.e., acculturation, acculturative stress) have an impact on
physiologic responses leading to maladaptation of the stress response as seen in
McEwen’s allostatic load theory would support the use of the psychosocial stressors of
acculturation and acculturative stress as markers of allostatic load.
Implications for Nursing Practice
As the country is transformed into a society where Mexican Americans are the
largest minority group, the U.S. health care system will need to be prepared to make
changes in the delivery of health care. Nurses, physicians, health care administrators,
and legislators will need to respond appropriately by planning how effective, culturally
appropriate health care will be delivered to a vulnerable population.
As posed by the Hispanic paradox (Palloni & Morenoff, 2001; Franzini; Ribble, &
Keddie, 2000), first generation Americans have comparable to better health outcomes as
non-Hispanic White Americans, making preventive care and health promotion vital to
first generation Americans’ transition into American culture. Maintaining the health of this
84
generally healthy population by implementing health promotion strategies such as weight
management, exercise, stress management, smoking avoidance and/or cessation, and
regular health screening in first generation Americans can result in keeping them free of
disease and provide opportunities for early recognition of disease. If they continue to
adopt health promoting behaviors as they age, transition, and adjust to the U.S.
mainstream culture, the group is likely to remain healthy. In addition, promoting healthy
behaviors in first generation Americans may result in healthier subsequent generations
as the elders impart their healthy behaviors to new generations.
First generation childbearing women are an excellent group to target for health
education and preventive care. Reaching these women, specifically women who are at
risk for GDM and later T2DM, during the pre-conception and prenatal care periods with
health education to prevent disease, weight management, mental health, and disease
risk assessments and screening will have an impact on their conception, pregnancy, and
their future health and that of their child. Targeting this group of women can help us
foster the positive influences of acculturation by supporting their opportunities to have
better access to health care, including greater use of preventive care and improved
educational opportunities. Ultimately, these types of services can contribute to better
health, higher earning potential and upward mobility (Perez-Escamilla, 2011; Akresh,
2007).
Advanced practice nurses are trained in health promotion and disease
prevention, making them important contributors in the planning of delivery of this type of
care. It is imperative that advanced practice nurses participate in research to investigate
the impact of psychosocial stress on metabolic response, plan and evaluate effective
interventions for appropriate care, disseminate health promotion information, participate
85
in establishing and evaluating efficient health promotion programs, as well as work at the
bedside promoting overall health and implementing preventive health care.
Recommendations for Future Research
This biobehavioral study provided insights into how cultural influences might alter
biological processes. The following research questions are worthy of being explored in
future research:
1. What is the relationship between level of acculturation and body mass index,
blood pressure, fasting blood sugar, glycosylated hemoglobin, triglycerides,
and waist circumference in normal, overweight, and obese women
contemplating pregnancy within one year?
2. What is the relationship between acculturative stress and markers of
allostatic load (i.e., cortisol, norepinephrine, epinephrine, and
dehydroepiandrosterone [DHEA])?
3. Is gestational diabetes a long-term predictor for metabolic syndrome? What is
the predictive value of gestational diabetes on metabolic syndrome?
4. Is acculturation useful as a measure of allostatic load?
5. What are the relationships among acculturation, stress, depression, and
anxiety?
6. What is the relationship between acculturation and dietary intake in
childbearing women?
7. Is acculturation a predictor of inflammatory response as measured by C-
reactive protein and tumor necrosis alpha?
8. Is acculturation a predictor of changes in metabolic response?
86
9. Are leptin and adiponectin levels different in normal weight women with and
without gestational diabetes during the different trimesters of pregnancy?
10. What are the relationships among leptin, adiponectin, C-reactive protein,
tumor necrosis alpha in normal, overweight, and obese women?
Summary
Although findings indicated that acculturation had no direct impact on
development of GDM in Mexican American women, acculturation was positively
associated with weight and leptin levels. The relationship between acculturative stress
and allostatic load requires additional investigation to provide insight on whether
acculturative stress can be used to quantify biological risks associated with the
development of GDM in Mexican American women.
As the U.S. transitions to a society where individuals who were historically
considered minorities become the majority, our health care system will face multiple
challenges as it adapts to provide high quality, culturally appropriate care for all.
Governments and policy makers will need to review and adapt policies to meet the
needs of these people. Advanced practice nurses and nurse researchers need to
continue to investigate and provide quality health care to foster holistic wellness and
promote accountability in individuals. Most importantly, individuals will need to become
accountable for their health and the health of their families, be active participants in their
communities, and take responsibility for their health by choosing behaviors that can lead
to better health outcomes.
This chapter reviewed the purpose and research questions that were presented
in Chapter 1, interpreted the findings presented in Chapter 4, presented and addressed
87
study limitations, discussed applications to theory development and implications for
nursing practice, and proposed recommendations for future research.
88
Appendix A.
Survey Instruments
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90
91
92
93
94
95
96
97
Appendix B
Letter from Office of Research Support
98
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