The study -- comprised of roughly 143,000 men and women -- ran from 1982 to 2001, tracking participants' responses to extensive lifestyle questionnaires. At the beginning of the survey, none of the participants showed symptoms of Parkinson's. By the end of the survey, 413 participants had developed the disease -- an occurrence strongly linked with being occupationally or otherwise exposed to pesticides.
The study's lead author, Alberto Ascherio of the Harvard School for Public Health, said, "Low-dose pesticide exposure was associated with a significant increase in risk for Parkinson's disease. I think this is one reason to be careful about using pesticides in general."
Environmental factors have long been suspected as a cause of Parkinson's, and Ascherio's study is the first large-scale population study to prove the link, though the study's design did not allow for determining how the duration, frequency or intensity of pesticide exposure influenced development of the disease. However, the study was able to prove that only pesticide exposure -- not exposure to coal dust, asbestos, exhaust, radioactive material or formaldehyde -- correlated with developing Parkinson's. Ascherio says the next step is figuring out specifically what chemicals in those pesticides cause the disease.