Cognitive decline and mortality in a community-based cohort: The Monongahela valley independent elders survey

OBJECTIVES: To compare, in a longitudinal cohort study, declines in specific cognitive domains on their ability to predict time to death, in the presence and absence of dementia, and to explore an explanatory role for vascular disease. DESIGN: Prospective population-based epidemiological study. SETTING: The mid-Monongahela valley of southwestern Pennsylvania from 1987 to 2002. PARTICIPANTS: Nine hundred eighty-nine community-dwelling adults aged 65 and older enrolled in the Monongahela Valley Independent Elders Survey. MEASUREMENTS: Biennial assessments of a range of cognitive domains for up to 12 years. Mortality was modeled as a function of decline in each domain, adjusting for vascular diseases and stratified according to age (≤75 (younger-old) and >75 (older-old)) using Cox proportional hazards modeling. RESULTS: Average annual declines in almost all cognitive domains were significant predictors of mortality in the cohort as a whole. However, after adjustment for dementia, only general cognition, processing speed, the language composite, and the executive function composite remained significant. Adjustment for vascular diseases did not alter the results. In the younger-old group, decline in memory (hazard ratio (HR)=21.4) and executive function (HR=25.5) remained strong predictors after adjustment for dementia and vascular disease. In the older-old group, decline in processing speed was a strong predictor of mortality before (HR=7.4) and after (HR=5.3) controlling for dementia and vascular diseases. CONCLUSION: Decline in most cognitive domains predicted mortality across the cohort, but declines in memory and learning were not independent of dementia. Different domains predicted mortality in the younger and older subgroups.