Effects of Diabetes Mellitus on the Risk of Parkinson Disease: An Updated Meta-Analysis with Cohort Studies

Purpose: This meta-analysis was conducted to analyze the effect of Diabetes Mellitus (DM) on the risk of Parkinson Disease (PD). Methods: Original prospective observational studies were searched through PubMed, Cumulative Index of Nursing and Allied Health Literature (CINAHL), ProQuest, Web of Science, Science Direct, Koreanstudies Information Service System (KISS), and DBpia published up to March 2020. The Relative Risks (RRs) were calculated using the random-effects model. Results: An integrated analysis of ten large population-based cohort studies, involving 10,730,117 participants, showed that patients with DM had a 30% higher risk of PD than those without DM (pooled RR=1.30, 95% Confidence Interval [CI]=1.14~1.48). Subgroup analyses based on the characteristics of the studies were conducted, and the association between DM and PD was significant in studies conducted in Asia (RR=1.30, 95% CI=1.01~1.69) and Europe (RR=1.45, 95% CI=1.09~1.94), and for patients with DM durations less than ten years (RR=1.31, 95% CI=1.27~1.37) and stroke (RR=1.16, 95% CI=1.03~1.31). Each study included in the analysis had methodologically good quality and showed no evidence of publication bias. Conclusion: DM resulted in a significantly increased risk of PD; therefore, prevention and early detection of PD in patients with DM should be encouraged.