A Longitudinal Community-Based Study of Chronic Illness, Cognitive and Physical Function, and Depression

Objective: Recent studies have tried to determine which aspects of chronic illness heighten the risk for depression, with functional impairment receiving the most attention. There is growing evidence that functional impairment accounts for most of the association between chronic illness and depression. This study examines the relative contribution of cognitive function, physical function, and chronic illness to depression 2 years later in a nationwide sample of elders aged 70 and older. Methods: This is a longitudinal community-based study of 5,289 elders completing two waves of assessment in the Asset and Health Dynamics among the Oldest Old study. Depression assessment included an abbreviated version of the CES-D and of the Composite International Diagnostic Interview (the CESD-8 and the CIDI-S). Cognitive function, physical function, and presence of chronic illness assessed at Wave 1 were examined as predictors of depression at Wave 2 while controlling for Wave 1 CESD-8 score. Results: In a full multivariate model, most baseline cognitive function, physical function, and chronic illness variables predicted depression as measured by the CESD-8 at Wave 2. The associations were markedly weaker between baseline variables and the Wave 2 CIDI-S. The Wave 1 CESD-8 score predicted all-cause mortality by Wave 2 (Z = 3.13; p > Z = 0.002) even after controlling for key health and functioning variables. Conclusion: Chronic illness, physical function, and cognitive function all independently predict depressive morbidity in late-life. The CIDI-S appeared less informative about these key relationships when compared to the CESD-8. The significance of depressive symptoms was demonstrated by their independent association with all-cause mortality at 2-year follow-up. (Am J Geriatr Psychiatry 2009; 17: 632-641)