The Role of Physical Activity and Obesity in the Occurrence of Major Cardiovascular Events and Mortality among a Low-Income Population with Diabetes

Abstract

EPIDEMIOLOGY The Role of Physical Activity and Obesity in the Occurrence of Major Cardiovascular Events and Mortality among a Low-Income Population with Diabetes Kimberly R. Glenn Dissertation under the direction of Professor Loren Lipworth Individuals with diabetes have a two-fold relative risk of death compared to those without diabetes, and cardiovascular disease (CVD) is the leading cause of death among people with diabetes. Physical activity has been recognized for its influence on both CVD risk and all-cause mortality (mortality) in the context of diabetes. However, most of the studies that have examined physical activity and CVD risk or mortality were conducted among predominantly white or male populations with a low prevalence or absence of CVD risk factors. Our study evaluated the independent associations between race, physical activity, sedentary time, and CVD risk or mortality among a racially-diverse population of diabetic men and women of generally low-socioeconomic status. Additionally, we examined whether these associations varied across levels of body mass index (BMI). Participants for all analyses were selected from among Southern Community Cohort Study (SCCS). Analyses of the association between physical activity, sedentary time and mortality were conducted among 15,645 black and white SCCS participants with diabetes. Participants with diabetes at enrollment who were 65 years old or greater on or before January 1, 2008 (“Medicare” group), and/or SCCS participants with diabetes at cohort enrollment recruited in Tennessee under the age of 65 (“TN HDDS” group) were included in analyses of the association between physical activity, sedentary time, and CVD. Incidence rates were age-adjusted and Cox proportional hazards models were constructed to generate hazard ratios (HR) and 95% confidence intervals (CI) for mortality and CVD risk in relation to race, physical activity and sedentary time. Interaction terms were added to the models to determine whether obesity, as measured by BMI, modified these relationships. During follow-up (median follow-up time: 6.2 years), 2,370 participants died of any cause. However, decreased physical activity and increased sedentary time were positively associated with mortality among all SCCS participants with diabetes (highest vs. lowest quartile of physical activity: HR, 0.64; 95% CI: [0.56-0.72]; highest vs. lowest quartile of sedentary time: HR, 1.25; 95% CI: [1.11-1.40]). Participants in the “Medicare” group (n = 1,880) and “TN HDDS” group (n = 498) had age-adjusted rates for CVD events and CVD-related deaths of 154.4 and 91.1 per 1,000 person-years, respectively. Race, physical activity and sedentary time were not associated with CVD risk in either population. Additionally, differences in body mass index did not modify the associations between physical activity, sedentary time, and CVD in either group (p-for interactions = 0.77 and 0.33, respectively). Though a clear, causal relationship was not observed between physical activity, sedentary time, and CVD in the two cohorts studied, we found that increasing physical activity and decreasing sedentary time increased survival among patients with diabetes regardless of race and sex in the SCCS.