Associations between abdominal adiposity, exercise, morbidity and mortality

Abstract

The increasing prevalence of abdominal obesity worldwide poses a serious public health problem and hence, presents a target for research designed to improve the assessment or treatment of abdominal obesity. Specifically, the first study in this thesis investigated the influence of age and gender on visceral (VAT) and abdominal subcutaneous adipose tissue (ASAT) for a given waist circumference (WC) in 481 men and women varying widely in age and BMI. Significant gender differences in VAT and ASAT for a given WC were observed, however, only the relationship between WC and VAT was substantially influenced by age. The second study examined whether the associations between VAT, ASAT and the metabolic syndrome (MetS) were altered depending on measurement methodology used to assess VAT and ASAT. The odds ratio (OR) for MetS was higher for total VAT volume (OR=7.26) and the partial volumes at T12-L1 (OR=7.46) and L1-L2 (OR=8.77) compared to the classic L4-L5 (OR=3.94) measurement. The OR for MetS was not substantially different among the ASAT measures (OR~2.6). Measurement site for VAT, but not ASAT, has a substantial influence on the magnitude of the association with MetS. The third study examined the independent associations between VAT, ASAT, liver fat and all-cause mortality in 291 men (97 decedents and 194 controls, mortality follow-up of 2.2±1.3 years). In a model including VAT, ASAT, liver fat, age, and length of follow-up, only VAT (1.93 [1.15-3.23]) remained a significant predictor of mortality. We concluded that VAT is a strong, independent predictor of all-cause mortality in men. The purpose of the final study was to determine the effect of aerobic exercise dose (energy expenditure) on WC in sedentary, overweight/obese postmenopausal women (n=424). The women were randomly assigned to a control group or one of three aerobic exercise groups that exercised at energy expenditures of 4-, 8-, or 12-kcal/kg body weight/week. By comparison to control, there were significant reductions in WC in the exercise groups (~3 cm, P <0.05), which were independent of weight loss. However, the amount of exercise performed was not associated with reductions in WC in a dose dependent manner.