Coronary heart disease (CHD) is the leading causes of combined morbidity and mortality worldwide. Metabolic syndrome is a cluster of cardiometabolic risk factors that predict cardiovascular disease, including CHD. Psychosocial factors, such as depression and social isolation, are increasingly recognized as risk factors for CHD and metabolic syndrome. However, this recognition is based on research in limited geographical areas, and sub-Saharan Africa is underrepresented in this literature. In addition, the mechanisms explaining the associations between psychosocial risk factors and poor cardiometabolic health are incompletely understood. Both behavioral mechanisms (e.g., physical activity, diet) and biological mechanisms (e.g., inflammation, metabolic changes) have been proposed, but their relative contributions are unknown. This dissertation addresses these gaps.
In Studies 1 and 2, we used data from the Nyakabare Parish Social Network Cohort, a cohort of individuals in a rural community in southwestern Uganda in which residents earn income primarily through subsistence farming, animal husbandry, and small-scale enterprise. In Study 1, we estimated the associations between probable depression (as measured by the Hopkins Symptom Checklist for Depression) and each of the five components of metabolic syndrome (i.e., elevated waist circumference, low high-density lipoprotein [HDL] cholesterol, elevated triglycerides, elevated blood pressure, and elevated glycated hemoglobin [HbA1c]), measured approximately two years later, using modified Poisson regression. We found probable depression was not associated with increased risk of any of these outcomes, although contrary to our hypothesis, there was weak evidence of a slight protective association between probable depression and elevated blood pressure (adjusted risk ratio [aRR] = 0.90, 95% confidence interval [CI] = 0.70, 1.15).
In Study 2, we estimated the associations between social isolation (vs. social integration, as measured by a composite measure combining marital status, close ties, and community group participation) and the same five components of metabolic syndrome as in Study 1, measured approximately two years later, using modified Poisson regression. We found social isolation was associated with increased risk of elevated blood pressure, specifically in men (aRR = 1.27, 95% CI: 0.93, 1.74). Contrary to our hypothesis, social isolation was associated with reduced risk of elevated waist circumference in both men (aRR = 0.30, 95% CI: 0.12, 0.75) and women (aRR = 0.69, 95% CI: 0.45, 1.06). In a secondary analysis, we found the specific domains of social isolation comprising social isolation affected metabolic syndrome components in unique ways.
In Study 3, we used data from the Framingham Heart Study – Offspring Cohort, a cohort of individuals in the United States developed to study risk factors for cardiovascular disease. We assessed the extent to which the components of metabolic syndrome (i.e., elevated waist circumference, low HDL cholesterol, elevated triglycerides, elevated blood pressure, and elevated fasting plasma glucose) mediated the association between probable depression and incident CHD. We used the counterfactual-based inverse odds ratio weighting method to estimate the total effect of probable depression on incident CHD, and decomposed the total effect into natural direct effects (NDE) and natural indirect effects (NIE) through putative mediators. We found probable depression was associated with incident CHD (adjusted hazard ratio [aHR] = 1.45, 95% CI: 0.93, 2.25), and this association was partially mediated by elevated waist circumference (NDE = 1.34, 95% CI: 0.76, 2.32; NIE = 1.08, 95% CI: 0.63, 1.91). Neither metabolic syndrome nor any other component of metabolic syndrome were found to be mediators.
Together, these three studies aid in better understanding the etiology of the associations between depression, social isolation, and poor cardiometabolic health. We offer evidence that the associations between depression and the components of metabolic syndrome previously observed in primarily high-income countries and urban areas do not necessarily extend to rural Uganda; that social isolation may affect health differently than depression, with variation by specific domain of social isolation; and that elevated waist circumference is a partial mediator of the association between depression and CHD. Further research is needed in this field, which is currently dominated by associational studies in limited geographical areas.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/44452 |
| Date | 18 May 2022 |
| Creators | Smith, Meghan Lee |
| Contributors | Gradus, Jaimie L. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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