Prospective cohort study of type 2 diabetes and the risk of Parkinson's disease.

Objective: To evaluate the association between type 2 diabetes and newly reported Parkinson's disease.

Research Design And Methods: Our study included 21,841 participants in the Physicians' Health Study, a cohort of U.S. male physicians. Diabetes and Parkinson's disease were self-reported via questionnaire. We used time-varying Cox regression to calculate adjusted relative risk (RR) for Parkinson's disease.

Results: Over 23 years, 556 individuals with Parkinson's disease were identified. Subjects with diabetes had an increased Parkinson's disease risk (multivariable-adjusted RR 1.34 [95% CI 1.01-1.77]). The association remained significant after exclusion of those with known vascular disease. The diagnosis of diabetes was clustered around the diagnosis of Parkinson's disease and was more apparent among men with short diabetes duration and those without complications from diabetes.

Conclusions: Results of this large prospective study in men do not suggest that diabetes is a preceding risk factor for Parkinson's disease. Whether the positive association may be explained by ascertainment bias or a common underlying biological mechanism remains to be established.