A report in the September issue of Archives of Neurology (one of the JAMA/Archives journals) shows that individuals whose occupation involves contact with pesticides appear to have an increased risk of having Parkinson’s disease.
According to background information in the article, the development of Parkinson’s disease related to chemical exposure was identified in the late 20th century. Occupations such as farming, teaching and welding have all since then been proposed to increase the risk of Parkinson’s disease. However, associations have been contradictory. Only a small number of earlier studies have investigated the direct relationship between occupational chemical exposure and disease risk.
The study was the work of Caroline M. Tanner, M.D., Ph.D., of the Parkinson’s Institute, Sunnyvale, Calif., and colleagues. It included 519 individuals with Parkinson’s disease and 511 controls. All participants were the same age and sex and lived in the same location. Their occupational history and exposure to toxins, including solvents and pesticides was surveyed.
Findings showed that working in agriculture, education, health care or welding was not associated with Parkinson’s disease. There was no association with any other specific occupation studied after adjustment for other factors.
Among the patients with Parkinson’s disease, 8.5 percent (44 individuals) reported pesticide exposure compared with 5.3 percent (27 individuals) in the control group. Occupational pesticide exposure was associated with an increased risk of the disease. “Growing evidence suggests a causal association between pesticide use and parkinsonism. However, the term ‘pesticide’ is broad and includes chemicals with varied mechanisms,” the authors explain, “Because few investigations have identified specific pesticides, we studied eight pesticides with high neurotoxic plausibility based on laboratory findings. Use of these pesticides was associated with higher risk of parkinsonism, more than double that in those not exposed.”
Three individual compounds were associated with a more than three-fold increased risk of Parkinson’s disease:
• an organochloride (2,4-dichlorophenoxyacetic acid)
• an herbicide (paraquat)
• an insecticide (permethrin)
In the laboratory, all three have been shown to have effects on dopaminergic neurons which are affected by Parkinson’s disease.
“This convergence of epidemiologic and laboratory data from experimental models of Parkinson’s disease lends credence to a causative role of certain pesticides in the neurodegenerative process,” the authors write in conclusion. “Other pesticide exposures such as hobby gardening, residential exposure, wearing treated garments or dietary intake were not assessed. Because these exposures may affect many more subjects, future attention is warranted.”
Arch Neurol 2009; 66:1106-1113.
Archives of Neurology
Written by Stephanie Brunner (B.A.)