Diabetes mellitus and risk of dementia in the Kungsholmen project

BACKGROUND: Research on diabetes mellitus as a risk factor for dementia and its main subtypes has produced conflicting results. The authors investigated the relationship between diabetes mellitus and risk of dementia, Alzheimer disease (AD), and vascular dementia (VaD). METHODS: A dementia-free cohort of 1,301 community dwellers aged 75 years and older in Stockholm, Sweden, was longitudinally examined twice over 6 years to detect dementia cases (Diagnostic and Statistical Manual of Mental Disorders-III-R diagnostic criteria). Cox proportional hazards models were used to analyze the data with adjustment for several potential confounders. RESULTS: During the 5,584 person-years of follow-up, 350 subjects developed dementia, including 260 AD and 49 VaD cases. Diabetes mellitus was associated with hazard ratios (HR) of 1.5 (95% CI 1.0 to 2.1, p = 0.04) for dementia, 2.6 (95% CI 1.2 to 6.1) for VaD, and 1.3 (95% CI 0.9 to 2.1) for AD. Patients who were treated with oral antidiabetic medications had HRs of 1.7 (95% CI 1.0 to 2.8, p = 0.04) for dementia and 3.6 (95% CI 1.3 to 9.5) for VaD. There were significant interactions of diabetes with severe systolic hypertension (> or =180 mm Hg) on dementia and its main subtypes, and of diabetes with heart disease on VaD. CONCLUSIONS: Diabetes mellitus increases the risk of dementia, and VaD in particular, in very old people. The risk for dementia and VaD is especially high when diabetes mellitus occurs together with severe systolic hypertension or heart disease.