Diabetes in patients with idiopathic Parkinson's disease

OBJECTIVE: Previous observational studies reported inconsistent results on the association between diabetes and Parkinson's disease, and data on the risk of developing incident diabetes in relation to Parkinson's disease are scarce. We aimed at comparing the diabetes prevalence between patients with or without Parkinson's disease and at exploring the risk of developing incident diabetes associated with Parkinson's disease. RESEARCH DESIGN AND METHODS: We used the U.K.-based General Practice Research Database (GPRD) to 1) compare the diabetes prevalence between Parkinson's disease cases and a matched comparison group free of Parkinson's disease between 1994 and 2005 and to 2) conduct a follow-up study with a nested case-control analysis to quantify the risk of developing new-onset diabetes in association with Parkinson's disease. RESULTS: The diabetes prevalence was similar in patients with and without Parkinson's disease (adjusted odds ratio [OR] 0.95 [95% CI 0.80-1.14]). In the cohort analysis (incidence rate ratio [IRR] 0.55 [95% CI 0.38-0.81]) and in the nested case-control analysis (adjusted OR 0.53 [95% CI 0.33-0.87]), the risk of developing diabetes was lower in patients with Parkinson's disease than in subjects without. The adjusted OR for patients with Parkinson's disease who were current levodopa users of five or more prescriptions was 0.22 (0.10-0.48) and was 1.11 (0.50-2.45) for Parkinson's disease patients not using levodopa. CONCLUSIONS: In this observational study, diabetes prevalence was closely similar between patients with Parkinson's disease and subjects without. The risk of developing incident diabetes was lower for patients with Parkinson's disease than for patients without, a finding that was limited to Parkinson's disease patients who were using levodopa.