Diabetes and cognitive decline in elderly African Americans: a 15-year follow-up study.

Background: Diabetes mellitus is associated with an increased risk for cognitive impairment and vascular factors seem to play a role in this relationship. In a sample involving elderly African Americans, we tested the hypothesis that diabetes accelerates cognitive decline and explored possible mediating mechanisms within a follow-up period of 15 years.

Methods: A total of 1,702 subjects, of whom 441 had diabetes, were given the community screening interview for dementia to measure cognitive functioning at six different time points spread over a 15-year follow-up period. Mixed effects models with repeated measures were used to examine the association of diabetes and vascular risk factors with cognitive scores over time.

Results: African American subjects with diabetes reported having a significant accelerated cognitive decline as compared with those without diabetes (P = .046), when controlling for basic demographics and baseline comorbid conditions (heart disease, hypertension, stroke, and depression). Adjusting for incident heart disease, and especially stroke, weakened this association (P = .098), thereby indicating a mediating effect of stroke on the association between diabetes and cognitive decline. However, when incident stroke was incorporated into the model, the effect for participants with diabetes increased greatly (P = .007).

Conclusions: Diabetes, mediated by cerebrovascular pathology, accelerates cognitive decline within a follow-up period of 15 years in a sample comprising African Americans.