Factors associated with obesity and metabolic syndrome in an ageing cohort of black women living in Soweto, Johannesburg (study of women in and entering endocrine transition [sweet])

Abstract

Background: Black South African women living in urban settings have the highest prevalence of obesity in the sub–Saharan African region, and consequently a high prevalence of cardiometabolic diseases. The risk factors for obesity and the metabolic syndrome are not well studied in this population group, and the inter–relationship between diseases risk factors for metabolic syndrome is poorly understood, in addition to whether one factor predominates. Aim: The aim is three–fold: (i) To assess the physical activity patterns of middle–aged, urban black South African women, and if these patterns are associated with metabolic outcomes; (ii) To examine the association between lifestyle and psycho–social factors and changes in body composition over 10 years in this population; and (iii) To identify risk factors for the various components of metabolic syndrome. Methods: Drawing on the longitudinal Birth to Twenty Plus cohort (a longitudinal study of the health and development of children and their families) data collected in 2003 and 2013 was used to address the respective aims of the thesis. In particular, data on (i) anthropometry; (ii) body composition; (iii) blood pressure; (iv) cardiometabolic markers; (v) environmental factors (physical activity, smoking and smokeless tobacco consumption, and alcohol consumption); (vi) psycho–social factors; (vii) socio–economic status; and (viii) education status was used. Analytical methods comprised of descriptive, correlations, comparisons, multivariable regression, and logistic regression. Paper 1 described the patterns, levels and correlates of physical activity in 977 African women. Paper 2 was a longitudinal study of the role of environmental and psycho–social factors in predicting changes in body composition over 10 years (N=430). Body composition from ultrasound and DXA analyses, blood pressure, cardiometabolic and demographic factors were measured in 702 black African women from Soweto, Johannesburg for paper 3, which was a descriptive, cross–sectional study using data from the 2011/13 wave of data collection. Results: The prevalence of obesity (48.0% (baseline) to 67.8% (follow–up)) and metabolic syndrome (40.0% (baseline) to 49.6% (follow–up) increased significantly over ten years. The majority of the population were classified as “active” according to global physical activity questionnaire criteria, and the domain that contributed most to overall weekly physical activity was walking for travel. Sitting time (mins/wk) was not different between the activity groups, but was positively associated with triglyceride levels and diastolic blood pressure. Total physical activity was inversely associated with fasting insulin, and physical activity in the work domain was associated with fat–free, soft–tissue mass. Two distinct groups of overweight/obese females were identified using body–size dissatisfaction and body–size discrepancy scores: one that was content with their body–size and one that wished to be leaner. Vigorous physical activity at baseline was inversely associated with absolute changes in all measures of adiposity. In subjects who underestimated their body–size at baseline (74.0 % of the study population) changes in total and peripheral levels of body fat were less than in subjects who correctly identified their body–size. In the group that underestimated body–size, more women wanted to be leaner than in the group who knew their body–size (60.1 % vs 47.5 %, p < 0.05). Logistic regression analysis demonstrated that adiponectin (odds ratio [95% CIs]: 0.84 [0.77, 0.92], p<0.0005) and abdominal subcutaneous fat (0.56 [0.39, 0.79], p=0.001) reduced metabolic syndrome risk whilst insulin resistance (1.31 [1.16, 1.48], p<0.0005) and trunk fat–free, soft–tissue mass (1.34 [1.10, 1.61], p=0.002) increased risk. Within this group of risk factors, the relationship of adiponectin with metabolic syndrome risk, when analysed across adiponectin hexiles, was the least affected by adjustment for the other risk factors. Conclusions: The findings of this thesis show that the majority of urban black South African women have a high prevalence of obesity and cardiometabolic disease risk factors despite being classified as ‘physically active’. However, the intensity of the respective domains of physical activity is unknown. As walking as a means of travel/transport is a major contributor to physical activity, future research should attempt to determine whether the intensity of this activity plays a role in the prevention of cardiometabolic diseases. It was also demonstrated that an underestimation of body–size is common and is associated with a lower gain in total body adiposity and a desire to lose weight in most of the participants. Finally, this thesis observed that adiponectin has a significant protective role against metabolic syndrome that is independent of other risk factors. The protective and augmentive effects of abdominal subcutaneous fat and lean trunk mass, respectively, on metabolic syndrome risk demonstrate the existence of novel interactions between body composition and cardiometabolic disease.