Age, body mass index, and functional illness

Objectives. This study examines the relationship between body mass index (BMI) and selected measures of functional illness and whether the relationship between BMI and these outcomes is stronger in advanced ages. Methods. Four measures of functional illness were examined in a national, longitudinal survey of noninstitutionalized adults. Tobit and Poisson models were used to estimate cross-sectional and longitudinal specifications. Results. BMI was related to functional illness but not in a linear form: Both obese and underweight persons manifested higher levels of functional illness on most outcomes during the baseline survey. Results from the change analyses, however, revealed that obesity was associated with more days hospitalized or ill in bed and an increase in functional limitations. Discussion. Obesity is associated with functional illness, but there is no evidence from these data that this relationship is stronger for older adults. Rather, the effect of obesity on some measures of functional illness is greater in the younger and middle ages.