OBJECTIVE To study whether diabetes onset in late life is a risk factor for dementia.

RESEARCH DESIGN AND METHODS We conducted a population-based matched cohort study using provincial health data from Ontario, Canada. Seniors with (n = 225,045) and without newly diagnosed diabetes (n = 668,070) between April 1995 and March 2007 were followed until March 2012 for a new diagnosis of dementia. Cox proportional hazards modeling was used to compare the risk of dementia between groups after adjusting for baseline cardiovascular disease, chronic kidney disease (CKD), hypertension, and other risk factors.

RESULTS Over this period, we observed 169,114 new cases of dementia. Individuals with diabetes had a modestly higher incidence of dementia (2.68 vs. 2.62 per 100 person-years) than those without diabetes. In the fully adjusted Cox model, the risk of dementia was 16% higher among our subgroup with diabetes (hazard ratio [HR] 1.16 [95% CI 1.15–1.18]). Adjusted HRs for dementia were 1.20 (95% CI 1.17–1.22) and 1.14 (95% CI 1.12–1.16) among men and women, respectively. Among seniors with diabetes, the risk of dementia was greatest in those with prior cerebrovascular disease (HR 2.03; 95% CI 1.88–2.19), peripheral vascular disease (HR 1.47; 95% CI 1.19–1.82), and CKD (HR 1.44; 95% CI 1.38–1.51), and those with one or more hospital visits for hypoglycemia (HR 1.73; 95% CI 1.62–1.84).

CONCLUSIONS In this population-based study, newly diagnosed diabetes was associated with a 16% increase in the risk of dementia among seniors. Preexisting vascular disease and severe hypoglycemia were the greatest risk factors for dementia in seniors with diabetes.