Cognitive Impairment, Depressive Symptoms, and Functional Decline in Older People

Abstract

OBJECTIVES-Although cognitive impairment and depressive symptoms are associated with functional decline, it is not understood how these risk factors act together to affect the risk of functional decline. The purpose of this study is to determine the relative contributions of cognitive impairment and depressive symptoms on decline in activity of daily living (ADL) function over 2 years in an older cohort. DESIGN-Prospective cohort study.SETTING-A U.S. national prospective cohort study of older people, Asset and Health Dynamics in the Oldest Old.PARTICIPANTS-Five thousand six hundred ninety-seven participants (mean age 77, 64% women, 86% white) followed from 1993 to 1995 MEASUREMENTS-Cognitive impairment and depressive symptoms were defined as the poorest scores: 1.5 standard deviations below the mean on a cognitive scale or 1.5 standard deviations above the mean on validated depression scales. Risk of functional decline in participants with depressive symptoms, cognitive impairment, and both, compared with neither risk factor, were calculated and stratified by baseline dependence. Analyses were adjusted for demographics and comorbidity.RESULTS-Eight percent (n = 450) of subjects declined in ADL function. In participants who were independent in all ADLs at baseline, the relative risk (RR) of 2-year functional decline was 2.3 (95% confidence interval (CI) = 1.7-3.1) for participants with cognitive impairment, 1.9 (95% CI = 1.3-2.6) for participants with depressive symptoms, and 2.4 (95% CI = 1.4-3.7) for participants with cognitive impairment and depressive symptoms. In participants who were dependent in one or more ADLs at baseline, RR of 2-year functional decline was 1.9 (95% CI = 1.2-2.8) for participants with cognitive impairment, 0.6 (95% CI = 0.3-1.3) for participants with depressive symptoms, and 1.5 (95% CI = 0.8-2.6) for participants with cognitive impairment and depressive symptoms.CONCLUSIONS-In participants with no ADL dependence at baseline, cognitive impairment and depressive symptoms are risk factors for decline, but that, in participants with dependence in ADL at baseline, cognitive impairment, but not depressive symptoms, is a risk factor for additional decline. The relationship between cognitive status and depressive symptoms and their effect on functional decline is of significant clinical and public health importance because they are common, frequently coexist, and may be treatable. For example, depressive symptoms are thought to exacerbate cognitive problems in older people and may be an independent risk factor for cognitive impairment; conversely, cognitive impairment may lead to depression. [2][3][4] Prior studies on the effect of cognitive impairment or depressive symptoms on functional decline have suggested that depressive symptoms and cognitive impairment are independently associated with functional decline, 4-13 but prior studies are limited because they have not taken into consideration that cognitive impairment and depressive symptoms are interrelated, have not studied ethnical...

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