Environmental risk factors and Parkinson's disease: a metaanalysis

The study aim was to examine the association between Parkinson's disease (PD) and exposure to environmental factors such as living in a rural area, well water use, farming, exposure to farm animals, or living on a farm, and pesticides. A series of metaanalyses of peer-reviewed studies were performed, using 16 studies for living in rural area, 18 studies for well water drinking, 11 studies for farming, and 14 studies for pesticides. Prior to the metaanalyses, all studies were reviewed and evaluated for heterogeneity and publication bias. Significant heterogeneity among studies was detected and combined odds ratio (OR) was calculated using the random and the fixed-effect models. The majority of the studies reported consistent elevation in the risk of PD with exposure to environmental factors such as rural living and farming. The combined OR for rural residence was 1.56 [95% confidence interval (95% CI) 1.18-2.07] for all the studies, and 2.17(95% CI 1.54-3.06) for studies performed in United States. The combined OR for well water use was 1.26 (95% CI 0.97-1.64) for all the studies, and 1.44(95% CI 0.92-2.24) for studies done in United States. The combined OR for farming, exposure to farm animals, or living on a farm was 1.42 (95% CI 1.05-1.91) for all studies, and 1.72(95% CI 1.20-2.46) for studies done in United States. The combined OR for pesticides exposure was 1.85(95% CI 1.31-2.60) for all studies, and 2.16(95% CI 1.95-2.39) for studies done in United States. Dose-response relationships could not be established due to the imprecise nature of the reported data. Our findings suggest that living in a rural area, drinking well water, farming, and exposure to pesticides may be a risk factor for developing PD.