HealthDay News — Exposure to pesticides or solvents is associated with an increased risk for Parkinson’s disease, results of a meta-analysis suggest.

An analysis of 89 prospective and case-control studies reveals that exposure to bug or weed killers and solvents resulted in a 33% to 80% increased risk for developing Parkinson’s disease, according to Gianni Pezzoli, MD of the Parkinson Institute, Istituti Clinici di Perfezionamento in Milan, and Emanuele Cereda, MD, PhD, IRCCS University Hospital San Matteo Foundation in Pavia, Italy.

However, the researchers warned the data is inconclusive, due to lack of definitive agreement between cohort and case-control studies, they reported in Neurology.

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The studies included in the analysis examined Parkinson’s incidence and exposure to pesticides, herbicides, insecticides, fungicides, rodenticides solvents, organochlorines, organophosphates, paraquat, maneb/mancozeb and DDT. All studies provided risk and precision estimates that linked Parkinson’s disease to pesticide or solvent exposure or to proxies of exposure.The researchers also determined risk based on exposure to farming, well-water drinking and rural living.

The researchers found that study quality was not a source of heterogeneity in prospective studies. Parkinson’s disease was associated with farming (RR 1.33; 95% CI: 1.14-1.56, P<0.001), and there was a highly significant correlation with pesticides in studies with self-reported Parkinson’s disease diagnosis, but not with DDT. 

In risk estimates for some exposures, study quality seemed to be a source of heterogeneity in case-control studies, with a reduction in heterogeneity frequently seen with higher study quality. In high-quality case-control studies, exposure to any-type pesticides, herbicides and solvents correlated with increased Parkinson’s disease risk.

Specifically, there was about a two-fold increase in risk with exposure to paraquat or maneb/mancozeb. Based on high-quality studies with more than 200 cases, heterogeneity was above 40% only for insecticides, organochlorines, organophosphates and farming. There was also a significant risk associated with rural living (1.51, 95% CI 1.13-2.03, P=0.006).

“The literature supports the hypothesis that exposure to pesticides or solvents is a risk factor for Parkinson’s disease,” the researchers wrote. They called for more studies to further analyze specific relationships between chemical exposure and neurologic injury.


  1. Pezzoli G, Cereda E “Exposure to pesticides or solvents and risk of Parkinson disease” Neurology 2013; 80: 2035-2041.