While the causes of Parkinson's disease are not fully known, many studies have suggested that factors other than inherited genes play a large role. Data suggests that chronic exposure to pesticides, even in low doses, could be a risk factor. To examine this association, researchers led by Alberto Ascherio, M.D., Dr.PH of the Harvard School of Public Health conducted a prospective study of Parkinson's disease among a large cohort of Americans.
They included male and female participants of the Cancer Prevention Study II Nutrition Cohort who, beginning in 1982, completed extensive lifestyle questionnaires that included questions about occupation and exposure to pesticides and other potentially harmful materials. The researchers focused their study on 143,325 individuals who completed a follow-up survey in 2001, responded to a question about lifetime occurrence of Parkinson's disease, and had no symptoms at baseline.
The researchers requested the medical records of all study participants who reported a new diagnosis of Parkinson's disease after 1992 - that is 10 or more years after the reported exposure to pesticides -- to independently confirm the diagnosis. 413 cases were included in this study, and statistical analyses were performed to determine the association between pesticide exposure and Parkinson's disease.
The risk of Parkinson's disease was 70 percent higher for people exposed to pesticides. Notably, a similar increase in risk was observed among people who were exposed because of their occupation, such as farmers, as among people not occupationally exposed, suggesting that home or garden use of pesticides is also deleterious. Also noteworthy, exposure to other environmental contaminants was not related to risk of Parkinson's disease.
The study was limited by lack of detailed information about the duration, frequency and intensity of pesticide exposure. However, because of its prospective design, provides much stronger evidence on a link between exposure to pesticides and Parkinson's disease than that so far available. Further, the results are in accordance with studies in experimental animals that have shown that compounds commonly used as pesticides can cause dopaminergic degeneration and motor abnormalities.
"The findings support the hypothesis that exposure to pesticides is a risk factor for Parkinson's disease," the authors conclude. Since this study did not have access to information on specific pesticides, they suggest, "future studies should seek to identify the specific compounds associated with risk."
Article: "Pesticide Exposure and Risk of Parkinson's Disease." Ascherio, Alberto; Chen, Honglei; Weisskopf, Marc; O'Reilly, Eilis; McCullough, Marjorie; Calle, Eugenia; Schwartzschild, Michael; Thun, Michael. Annals of Neurology; July 2006; (DOI: 10.1002/ana.20904)