Cognitive scores, even within the normal range, predict death and institutionalization

Abstract

Background: Dementia is a predictor of death and institutionalization. It is less clear if variations in cognition within the normal range predict adverse outcomes. Objective: To determine if variation at the high end of cognitive test scores predicts mortality or institutionalization, independent of the effect of potential confounders. Design: Secondary analysis of the Canadian Study of Health and Aging, a population-based longitudinal study with an initial data collection in 1991 and follow-up five years later. Setting: Community-dwelling seniors living in Canada. Participants: 9008 consenting seniors were sampled from representative population registries in Canada. Measures: Age, gender, marital status, the Mini-Mental State Examination, self-rated health, and activities of daily living. Outcomes: Death or institutionalization over the five years of follow-up. Results: Mini-Mental State Examination scores predicted mortality and institutionalization. The unadjusted odds ratio of mortality was 0.85 (95% confidence interval 0.84, 0.86) per point on the Mini-Mental State Examination, and the adjusted odds ratio was 0.95 (95% confidence interval 0.93, 0.97). The unadjusted odds ratio for institutionalization was 0.83 (95% confidence interval 0.82, 0.85), and the adjusted odds ratio was 0.91 (95% confidence interval 0.90, 0.94). This effect was present even in analyses restricted to those within the normal range of Time 1 Mini-Mental State Examination scores. Conclusions: Low normal cognitive test scores predict adverse outcomes. Clinicians should consider close clinical follow-up of those with low normal cognitive test scores. Further research is needed to target seniors for follow-up and possible intervention to decrease mortality and institutionalization risk.