Pesticide exposure and risk of Parkinson's disease: Dose-response meta-analysis of observational studies

The cause of late onset Parkinson's disease (PD) remains unknown. Evidence suggested that lifelong exposure to pesticides might contribute to the development of neurodegenerative diseases, but the results were controversial. Relevant studies were identified by searching PubMed and Web of Science through September 2017. We included cohort and case-control studies reporting relative risks (RRs) or odds ratios (ORs) with 95% confidence intervals (CIs) of three or more categories of pesticide exposure and PD. Ten articles with 13 reports (3 for cumulative exposure, 10 for duration exposure) were included. A nonlinearity association was seen between duration exposure and PD risk (P = 0.01 for nonlinearity). The summary ORs of developing PD for 5 and 10 years of duration exposure were 1.05 (95% CI: 1.02-1.09) and 1.11 (95% CI: 1.05-1.18), respectively. Sensitivity analyses with different effect models yielded similar results, and omission of any single study did not change the results. The 5 and 10 years of duration pesticide exposure were associated with a 5% and 11% augment in the risk of PD. Further high-quality cohort studies were required to validate a causal relationship.