Age-related changes in weight and body composition: implications for health in the elderly

Abstract

The objective of this thesis was to examine age-related changes in weight and body composition as they relate to health in older adults. This thesis was completed in manuscript format and consists of two studies, both of which are based on the Cardiovascular Health Study (CHS) cohort. The CHS is a prospective cohort study of community-dwelling older (≥65 years) men and women who were followed for 8 years. The first manuscript examined whether physical activity (PA) attenuates age-related weight loss in the elderly. Mixed modeling procedures were employed to create body weight trajectory curves for the 8 year follow-up period according to physical activity level in a sample of 4512 CHS participants. Body weight declined over the follow-up period in all physical activity groups, with an accelerated weight loss occurring in the final years of follow-up. Over the 8 year follow-up, body weight was reduced by 2.72 kg in the least active PA quartile. Compared to the least active quartile, weight loss was attenuated by 0.55 kg (20%), 0.80 kg (29%), and 0.69 kg (25%) within the second through fourth physical activity quartiles. Therefore, participation in modest amounts of PA attenuated age-related weight loss by approximately 25%. The second manuscript examined whether sarcopenic-obesity is a stronger predictor of cardiovascular disease (CVD) than either sarcopenia or obesity alone, and whether muscle mass or strength is a stronger marker of CVD risk. CHS participants who were free of CVD at baseline (n=3400) were classified as normal, sarcopenic, obese, or sarcopenic-obese based on measures of waist circumference and either muscle mass or strength. Participants were followed for CVD development over 8 years and proportional hazard regression models were used to compare risk estimates for CVD after adjustment for covariates. When based on measures of waist circumference and muscle mass, CVD risk was not increased in sarcopenic, obese, or sarcopenic-obese groups in comparison to the group with a normal body composition. When categorized based on waist circumference and muscle strength, CVD risk was significantly increased (by 38%) in the sarcopenic-obese group but not in either the sarcopenic or obese groups. Thus, sarcopenic-obesity, based on muscle strength, was associated with increased CVD risk implying that strength is more important than muscle mass for cardiovascular health in old age. In summary, the findings of this thesis support the continuation of public health efforts to promote regular PA and balanced nutrition to assist with maintenance of optimal body composition and weight through adulthood and into old age.