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.