Dr. Alexis Elbaz of the French National Institute for Health and Medical Research and University Pierre et Marie Curie said the study involved people with the French health insurance organization for agricultural workers who were frequently exposed to pesticides.
The study leader said that by interviewing participants, visiting farms and collecting data on pesticide exposure, occupational health physicians constructed a detailed lifetime exposure history to pesticides.
The study, published in the Annals of Neurology, found that Parkinson's disease patients had been exposed to pesticides through their work more frequently and for a greater number of years/hours than those without Parkinson's disease.
Among the three main classes of pesticides -- insecticides, herbicides, fungicides -- researchers found the largest difference for insecticides: men who had used insecticides had a two-fold increase in the risk of Parkinson's disease.
Celebrity Families of 2014 [PHOTOS]