Pesticide Exposure Link to Parkinson’s Disease Strengthened

(Beyond Pesticides, June 8, 2009)

A new epidemiological study finds that Parkinson’s disease patients who have been exposed to pesticides through their work show elevated rates of the disease. The researchers find that French farmworkers have nearly double the risk for the disease if exposed to pesticides, with a dose-effect for the number of years of exposure. When they looked at the three major classes of pesticides (insecticides, fungicides and herbicides), they find that the farmworkers who used insecticides had over a two-fold increase in the risk of Parkinson’s disease. A slightly higher risk is found for exposure to organochlorine insecticides. According to the study, these associations are stronger in men with older onset Parkinson’s disease than in those with younger onset Parkinson’s.

The study, “Professional Exposure to Pesticides and Parkinson’s Disease,” published in Annals of Neurology, involved individuals affiliated with the French health insurance organization for agricultural workers who were frequently exposed to pesticides in the course of their work. Occupational health physicians constructed a detailed lifetime exposure history to pesticides by interviewing participants, visiting farms, and collecting a large amount of data on pesticide exposure. These included farm size, type of crops, animal breeding, which pesticides were used, time period of use, frequency and duration of exposure per year, and spraying method.

“Our findings support the hypothesis that environmental risk factors such as professional pesticide exposure may lead to neurodegeneration,” notes lead study author Alexis Elbaz M.D., Ph.D., of Inserm, the national French institute for health research in Paris, and the University Pierre et Marie Curie.

The second most common neurodegenerative disease affecting more than one million people in the U.S., Parkinson’s disease occurs when nerve cells in the substantia nigra region of the brain are damaged or destroyed and can no longer produce dopamine, a nerve-signaling molecule that helps control muscle movement.

In the past year several studies have been published that make the connection that Parkinson’s disease is caused by a combination of environmental risk factors such as pesticide exposure and genetic susceptibility. For example, residential exposure to an agriculture application of the fungicide maneb and the herbicide paraquat significantly increases the risk of developing Parkinson’s disease, according to a University of California, Berkeley study. A study by University of California, Los Angeles (UCLA) researchers found pesticide exposure and genetic variability in the dopamine transporter (DAT), a protein that plays a central role in dopaminergic neurotransmission of the brain, interact to significantly increase the risk factor for Parkinson’s disease. Another study by UCLA researchers found chronic exposure to commonly used dithiocarbamate fungicides, such as ziram, contribute to the development of Parkinson’s disease. A University of Texas study found a strong correlation between Parkinson’s disease patients and the use of the pesticide rotenone. In addition, Duke University and University of Miami researchers studying related individuals who share environmental and genetic backgrounds found a significant association between Parkinson’s disease and use of herbicides and insecticides, such as organochlorines and organophosphates.