Convergence of body mass with aging: The longitudinal interrelationship of health, weight, and survival

There has been ongoing debate about the health risks associated with increased body weight among the elderly population. One issue has not been investigated thoroughly is that body weight changes over time, as both the reasons and results of, the development of chronic diseases and functional disabilities. Structural models have the ability to unravel the complicated simultaneous relationship between body weight, disability, and mortality along the aging process. Using longitudinal data from the Medicare Current Beneficiary Survey from 1992 to 2001, we constructed a structural model to estimate the longitudinal dynamic relationship between weight, chronic diseases, functional status, and mortality among the aging population. A simulation of an age cohort from 65 to 100 was conducted to show the changes in weight and health outcomes among the cohorts with different baseline weight based on the parameters estimated by the model. The elderly with normal weight at age 65 experience higher life expectancy and lower disability rates than the same age cohorts in other weight categories. The interesting prediction of our model is that the average body size of an elderly cohort will converge to the normal weight range through a process of survival, senescence, and behavioral adjustment.