Diabetes mellitus and risk of Alzheimer disease and decline in cognitive function

Background: Few prospective studies have assessed diabetes mellitus as a risk factor for incident Alzheimer disease (AD) and decline in cognitive function. Objective: To evaluate the association of diabetes mellitus with risk of AD and change in different cognitive systems. Design: Longitudinal cohort study. Participants: For up to 9 years, 824 older (those >55 years) Catholic nuns, priests, and brothers underwent detailed annual clinical evaluations. Main Outcome Measures: Clinically diagnosed AD and change in global and specific measures of cognitive function. Results: Diabetes mellitus was present in 127 (15.4%) of the participants. During a mean of 5.5 years of observation, 151 persons developed AD. In a proportional hazards model adjusted for age, sex, and educational level, those with diabetes mellitus had a 65% increase in the risk of developing AD compared with those without diabetes mellitus (hazard ratio, 1.65; 95% confidence interval, 1.10-2.47). In random effects models, diabetes mellitus was associated with lower levels of global cognition, episodic memory, semantic memory, working memory, and visuospatial ability at baseline. Diabetes mellitus was associated with a 44% greater rate of decline in perceptual speed (P=.02), but not in other cognitive systems. Conclusions: Diabetes mellitus may be associated with an increased risk of developing AD and may affect cognitive systems differentially.