The role of cerebrovascular disease and the association between diabetes mellitus and dementia among aged medicare beneficiaries.

OBJECTIVE: The aim of this study is to assess whether diabetes mellitus is associated with overall dementia and its subtypes (Alzheimer's disease and vascular dementia) among the elderly and to identify the role of cerebrovascular disease in the association between diabetes and dementia.

METHODS: In a retrospective cross-sectional study, 5160 community-dwelling and institutionalized Medicare beneficiaries aged 65 years or over without health maintenance organization enrollment from the Medicare Current Beneficiary Survey in 2010 were included. The International Classification of Diseases-9 codes were used to identify the outcome and independent variables from the Medicare claims. The key predictor was diabetes mellitus and the outcomes were overall dementia and its subtypes. Logistic regression was employed to assess the association between dementia and diabetes after adjusting for age, gender, race, education, income, smoking status, and Charlson Comorbidity Index.

RESULTS: After adjusting for potential confounders, diabetes mellitus was significantly associated with overall dementia (odds ratio [OR] = 1.42; 95% confidence interval [CI], 1.14-1.77), vascular dementia (OR = 1.29; 95% CI, 1.02-1.64), and Alzheimer's disease (OR = 1.51, 95% CI, 1.10-2.09). The OR decreased to 1.26 (95% CI, 1.01-1.58) for overall dementia, controlling for cerebrovascular disease. The associations between diabetes mellitus and vascular dementia (OR = 1.13, 95% CI, 0.89-1.44) and Alzheimer's disease (OR = 1.39, 95% CI, 1.00-1.92) were no longer statistically significant once cerebrovascular disease was controlled.

CONCLUSIONS: The association between diabetes mellitus and dementia is only partially mediated through cerebrovascular disease, suggesting that diabetes mellitus is associated independently with overall dementia among the elderly, but not with vascular dementia and Alzheimer's disease.