Alcohol consumption and risk for Parkinson's disease: a systematic review and meta-analysis.

The possibility that alcohol consumption should be considered as a "protective factor" for Parkinson's disease (PD) has been suggested by several case-control studies. However, other case-control studies and data from prospective longitudinal cohort studies have been inconclusive. We carried out a systematic review which included all the eligible studies published on PD risk related with alcohol consumption, and conducted a meta-analysis according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. The systematic review was performed using two databases, and the meta-analysis of the eligible studies with the software Meta-Disc1.1.1. Heterogeneity between studies was tested with the Q-statistic. The meta-analysis included 26 eligible retrospective case-control studies (8798 PD patients, 15,699 controls) and 5 prospective longitudinal cohort studies (2404 PD patients, 600,592 controls) on alcohol consumption and PD. In retrospective case-control studies the frequency of PD patients never drinkers was higher and the frequency of heavy + moderate drinkers was lower [diagnostic OR (95% CI) 1.33(1.20-1.48) and 0.74(0.64-0.85)], respectively, when compared to healthy controls. In contrast, in prospective studies, the differences were not significant with the exception of a trend towards a higher frequency of non-drinkers in PD women and a significantly lower frequency of moderate + heavy drinkers in PD men in those studies which stratified data by gender. The present meta-analysis suggests an inverse association between alcohol consumption and PD, which is supported by the results of case-control studies but not clearly by prospective ones.