Joint effects of adiposity and physical activity on incident mobility limitation in older adults

OBJECTIVES: To examine joint associations of physical activity and adiposity measures (body mass index (BMI), waist circumference, percentage body fat) with incident mobility limitation. DESIGN: Prospective observational cohort study. SETTING: Memphis, Tennessee and Pittsburgh, Pennsylvania. PARTICIPANTS: Two thousand nine hundred and eighty-two black and white men and women aged 70 to 79 participating in the Health, Aging and Body Composition (Health ABC) study. MEASUREMENTS: Mobility limitation was defined as reported difficulty walking one-quarter of a mile or climbing 10 steps during two consecutive semiannual assessments over 6.5 years. Three measures of adiposity were included in this study: BMI, total percentage body fat, and waist circumference. Physical activity was assessed using a modified leisure-time physical activity questionnaire. RESULTS: Forty-six percent of the cohort developed mobility limitation. White and black men with a high BMI (>= 30 kg/m(2)), high total percentage body fat (>31.3%), or high waist circumference (>= 102 cm) had an approximately 60%, 40%, and 40%, respectively, higher risk of incident mobility limitation than those with low adiposity. In women, high adiposity was also associated with a significantly higher mobility limitation risk than in those with low adiposity. Low physical activity (lowest quartile) was associated with a 70% higher risk of mobility limitation in all groups. Persons with high adiposity and low physical activity were at particularly high risk of mobility limitation. People with high adiposity who were physically active had an equally high risk of mobility limitation as inactive people with low adiposity. CONCLUSION: High adiposity and low self-reported physical activity predicted the onset of mobility limitation in well-functioning older persons. Preventing weight gain in old age and promoting physical activity in obese and non-obese older persons may therefore be effective strategies to prevent mobility loss and future disability.