Five-year mortality in relation to dementia and cognitive function in 95-year-olds

Background: Dementia is a known predictor of mortality, but most studies include small numbers of participants above age 90. The influence of dementia or cognition on mortality in this age group is therefore uncertain. Objective: To examine 5-year mortality in relation to dementia and cognitive performance at age 95. Methods: A population sample of 338 individuals examined at age 95 was followed to age 100. Dementia was diagnosed according to DSM-III-R criteria. Cognitive function was measured using the Mini-Mental State Examination (MMSE). Information on severe physical disorders was obtained from the Swedish Hospital Discharge Register, and date of death from the Swedish Population Register. Results: Five-year mortality was higher in 95-year-olds with dementia than in 95-year-olds without dementia (96% vs 73%; p < 0.0001), even when adjusting for severe physical disorders. A Cox regression analysis with calculation of population attributable risk (PAR), calculated from adjusted relative risks, showed that mortality was predicted by dementia (PAR 42%), cardiac disease (PAR 17%), cancer (PAR 6%), and male sex (PAR 7%), but not by stroke. Among the subjects without dementia, cognitive performance measured using the MMSE (n=133 with complete tests; 81% of the subjects without dementia) predicted mortality. For each point increase in the MMSE, mortality decreased by 13%. Conclusions: In 95-year-olds, dementia, as well as cognitive performance in the subjects without dementia, influences mortality. When controlling for other severe medical conditions we found dementia to be the leading cause of deaths among the oldest old. The reason why dementia and cognitive function predict life expectancy requires further elucidation.