The effect of obesity on disability vs mortality in older Americans

Background: The association between obesity and mortality is reduced or eliminated in older subjects. In addition to mortality, disability is an important health outcome. The objectives of this study were to examine the association between body mass index (BMI), calculated as weight in kilograms divided by height in meters squared, and subsequent disability and mortality among older Americans, as well as to estimate the effect of BMI on life expectancy and disability-free life expectancy among older Americans. Methods: We studied 8359 non-Hispanic white Americans, 1931 African Americans, and 2435 Mexican Americans 65 years or older who were not disabled at baseline from 5 sites of the Established Populations for Epidemiologic Studies of the Elderly. Measures included BMI, medical conditions, activities of daily living, and demographic information. Cox proportional hazards regression analysis was used to estimate the hazard ratios (HRs) for subsequent disability and mortality during 7 years of follow-up. Total life expectancy and disability-free life expectancy were estimated using the interpolation of Markov chain approach. Results: The lowest HR (1.02; 95% confidence interval [CI], 0.94-1.10) for disability was at a BMI of 25 to less than 30. Subjects with BMIs of lower than 18.5 or 30 or higher at baseline were significantly more likely to experience disability during the follow-up period. In contrast, the lowest HRs for mortality were seen among subjects with BMIs of 25 to less than 30 (HR, 0.78; 95% CI, 0.72-0.85) and 30 to less than 35 (HR, 0.80; 95% CI, 0.72-0.90), with subjects with BMIs of lower than 25 or 35 or higher experiencing higher hazards for mortality. Disability-free life expectancy is greatest among subjects with a BMI of 25 to less than 30. Conclusion: Assessments of the effect of obesity on the health of older Americans should account for mortality and incidence of disability.