Racial differences on association of depressive symptoms with combined basic and instrumental activities of daily living

Background: Depressive symptoms are predictive of multiple degenerative diseases in older age adults. However, the association of depressive symptoms with onset and progression of disability have not been studied. Methods: In a cohort of community-dwelling, older black and white adults, 5,446 initially nondisabled subjects were followed annually for disability between 2000 and 2008. Depressive symptoms were assessed at baseline using a summary measure of 10-item version of the Center for Epidemiologic Survey-Depressive symptoms scale. The disability outcome was based on a summary measure of 13 basic and instrumental activities of daily living, and analyzed using a two-part regression model for onset and progression of disability. Results: During follow-up, 44% of blacks and 35% of whites reported onset of disability. After adjusting for confounders, depressive symptoms were associated with increased odds of disability onset in blacks (odds ratio = 1.12, 95% confdence interval, 1.07-1.18) and whites (odds ratio = 1.21, 95% confdence interval, 1.08-1.36). The odds of disability onset associated with depressive symptoms also increased significantly over time in whites (odds ratio = 1.06, 95% confdence interval, 1.04-1.09), but not in blacks. In addition, depressive symptoms were associated with an increasing rate of progression of disability in whites (rate ratio = 1.08, 95% confdence interval, 1.06-1.09), but not in blacks. Conclusions: Depressive symptoms increased the risk of onset of disability in blacks and whites. This risk tended to increase over time only among whites. A similar race-specific pattern was observed for time-dependent changes due to depressive symptoms in the rate of progression in disability after onset.