Risk of Parkinson Disease in Diabetes Mellitus: An Updated Meta-Analysis of Population-Based Cohort Studies

Previous meta-analysis has identified the associations between diabetes mellitus (DM) and the risk of Parkinson disease (PD). However, the results are still debatable. The purpose of this study is to perform an updated meta-analysis to investigate the up-to-date pooling evidence based on published population-based cohort studies and assess the association between DM and the risk of PD. Electronic database including Pubmed and Embase were searched to identify cohort studies published before October, 2015. Studies were selected if they reported the risk estimates for PD associated with DM. We pooled the adjusted effect estimates using random-effects metaanalysis. Funnel plot, Begg, or Egger test as well as Duval and Tweedie trim-and-fill approach were applied to assess publication bias. A total of 7 population-based cohort studies, representing 1,761,632 individuals were included in the meta-analysis. The pooled adjusted relative risk (RR) of PD associated with DM was 1.38 (95% CI 1.181.62, P<0.001). An effect was consistent in female (RR 1.50 95% CI 1.07-2.11, P = 0.019) and in male (RR 1.40, 95% CI 1.17-1.67). The association was similar when stratified by study quality, research region, study design, sample size, published year, diabetes duration, and baseline age. The trim-and-fill approach confirmed the robutness of the result (RR 1.31, 95% CI 1.09-1.57, P = 0.015). Our findings based on population-based cohort studies indicate that diabetes is associated with increased PD risk by about 38%. More large-scale prospective studies are warranted to further clarify this association and its mechanism.