Parkinson's disease and pesticide exposure--a new assessment.

Parkinson's disease (PD) is an idiopathic disease and its pathological feature is a loss of pigmented neurons in the substantia nigra. Some commonly used pesticides possess neurotoxicity, and exposure to such compounds may trigger mechanisms similar to those in the development of idiopathic PD. We conducted a systematic review of epidemiological studies, aiming at a critical evaluation of the association between the development of PD and pesticide exposure. Reported effect sizes (ES) in the relevant studies were pooled into the meta-analysis to derive summary ES. The summary ES suggested a significantly positive association between PD and overall pesticide use (non-occupational and/or occupational pesticide use) [1.42; 95% confidence interval (CI) 1.32 to 1.52, the fixed-effects model], as well as between PD and occupational pesticide exposure (1.49 with a 95% CI of 1.34-1.66). Both occupational herbicide and occupational insecticide exposure showed a significant association with PD. The results of the meta-analysis reported in this study suggest the existence of a statistically positive association between PD and pesticide exposure. The majority of the studies that were pooled in the meta-analysis were case-control design with very few cohort studies and most with poor exposure characterization thus, any further case-control studies using similar methodologies are unlikely to have a significant impact or understanding on the currently-reported association between pesticide exposure and the development of idiopathic PD. Therefore, we believe that if further epidemiological studies are going to be conducted in the area, they should be prospective cohort studies that will include accurate exposure assessment.