Abstract
OBJECTIVES: To determine the concurrent influence of depressive symptoms, medical conditions, and disabilities in activities of daily living (ADLs) on rates of decline in cognitive function of older Americans. DESIGN: Prospective cohort. SETTING: National population based. PARTICIPANTS: A national sample of 6,476 adults born before 1924. MEASUREMENTS: Differences in cognitive function trajectories were determined according to prevalence and incidence of depressive symptoms, chronic diseases, and ADL disabilities. Cognitive performance was tested five times between 1993 and 2002 using a multifaceted inventory examined as a global measure (range 0-35, standard deviation (SD) 6.0) and word recall (range 0-20, SD 3.8) analyzed separately. RESULTS: Baseline prevalence of depressive symptoms, stroke, and ADL limitations were independently and strongly associated with lower baseline cognition scores but did not predict future cognitive decline. Each incident depressive symptom was independently associated with a 0.06-point lower (95% confidence interval (CI)=0.02-0.10) recall score, incident stroke with a 0.59-point lower total score (95% CI=0.20-0.98), each new basic ADL limitation with a 0.07-point lower recall score (95% CI=0.01-0.14) and a 0.16-point lower total score (95% CI=0.07-0.25), and each incident instrumental ADL limitation with a 0.20-point lower recall score (95% CI=0.10-0.30) and a 0.52-point lower total score (95% CI=0.37-0.67). CONCLUSION: Prevalent and incident depressive symptoms, stroke, and ADL disabilities contribute independently to poorer cognitive functioning in older Americans but do not appear to influence rates of future cognitive decline. Prevention, early identification, and aggressive treatment of these conditions may ameliorate the burdens of cognitive impairment.