Pesticide exposure and risk for Parkinson's disease

Our plain-English summary of Pesticide exposure and risk for Parkinson's disease, by A. Ascherio, H. Chen, M.G. Weisskopf, et al (Annals of Neurology, 2006).

The study

• Authors: A. Ascherio, H. Chen, M.G. Weisskopf, E. O'Reilly, M.L. McCullough, E.E. Calle, M.A. Schwarzschild, M.J. Thun
• Journal: Annals of Neurology
• Published: 2006;60(2):197-203
• Cited by: 280 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: Chronic, low-dose exposure to pesticides is suspected to increase the risk for Parkinson's disease (PD), but data are inconclusive.

Methods: We prospectively examined whether individuals exposed to pesticides have higher risk for PD than those not exposed. The study population comprised participants in the Cancer Prevention Study II Nutrition Cohort, a longitudinal investigation of US men and women initiated in 1992 by the American Cancer Society. Follow-up surveys were conducted in 1997, 1999, and 2001. The 143,325 individuals who returned the 2001 survey and did not have a diagnosis or symptoms of PD at baseline (1992) were included in the analyses.

Results: Exposure to pesticides was reported by 7,864 participants (5.7%), including 1,956 farmers, ranchers, or fishermen. Individuals exposed to pesticides had a 70% higher incidence of PD than those not exposed (adjusted relative risk, 1.7; 95% confidence interval, 1.2-2.3; p = 0.002). The relative risk for pesticide exposure was similar in farmers and nonfarmers. No relation was found between risk for PD and exposure to asbestos, chemical/acids/solvents, coal or stone dust, or eight other occupational exposures.

Interpretation: These data support the hypothesis that exposure to pesticides may increase risk for PD. Future studies should seek to identify the specific chemicals responsible for this association.

In plain English

This prospective cohort study asked whether people reporting pesticide exposure later developed Parkinson's disease more often. It followed 143,325 US men and women in the American Cancer Society's Cancer Prevention Study II Nutrition Cohort who were free of Parkinson's disease in 1992. In 1982 they had been asked whether they had current or past regular exposure to pesticides/herbicides and eleven other agents, including asbestos. There were 413 new confirmed cases. Pesticide exposure was reported by 7,864 participants (5.7%). Adjusted for age, sex and smoking, this group had a 70% higher incidence of Parkinson's disease than the unexposed (relative risk 1.7; 95% confidence interval 1.2 to 2.3). With further adjustment it was 1.8 (1.3 to 2.5). The risk was similar in farmers and nonfarmers. No relation was found between Parkinson's disease and asbestos or the other exposures, which the article reports in a figure. The text supplied for this summary includes only that figure's caption, so no asbestos numbers are available here. The authors concluded the data support the hypothesis that pesticide exposure may increase risk. They noted missing detail on exposure intensity and specific pesticides, and no exposure updates after 1982.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: prospective cohort study
• Who was studied: 143,325 US men and women in the American Cancer Society's Cancer Prevention Study II Nutrition Cohort (begun 1992). All returned the 2001 survey and had no Parkinson's disease diagnosis or symptoms at the 1992 baseline. Follow-up ran to 2001, and 413 incident Parkinson's disease cases were included.
• Exposure: In 1982, participants were asked whether they had current or past regular exposure to each of twelve agents. The main exposure studied was pesticides/herbicides. The other agents included asbestos, chemicals/acids/solvents, coal or stone dust, diesel exhaust, formaldehyde and wood dust. Exposure information was not updated after 1982.
• Main results:
  • Pesticide exposure was reported by 7,864 participants (5.7%), including 1,956 farmers, ranchers, or fishermen.
  • People exposed to pesticides had a 70% higher incidence of Parkinson's disease than those not exposed, adjusted for age, sex and smoking (relative risk 1.7; 95% CI 1.2 to 2.3).
  • With adjustment for further potential confounders, the relative risk for people exposed to pesticides was 1.8 (95% CI 1.3 to 2.5).
  • The relative risk for pesticide exposure was similar in farmers and nonfarmers.
  • No relation was found between Parkinson's disease risk and exposure to asbestos, chemicals/acids/solvents, coal or stone dust, or eight other occupational exposures.
  • Among pesticide-exposed people who reported 10 or more years of exposure, the multivariate relative risk was 2.3 (95% CI 1.1 to 4.9). This was not significantly different from those with shorter exposure (RR 2.1; 95% CI 0.7 to 6.5) or missing duration (RR 1.7; 95% CI 1.2 to 2.5).
  • In a sensitivity analysis that counted participants who refused medical record review as confirmed cases, the relative risk for pesticide exposure was 1.8 (95% CI 1.4 to 2.4).
• The authors' conclusion: The authors concluded that these data support the hypothesis that exposure to pesticides may increase risk for Parkinson's disease.
• Limitations the authors state:
  • The study lacked detailed information about the duration, frequency and intensity of exposure, and about which specific pesticides were involved.
  • Exposure information was not updated after 1982, so more recent pesticide exposure could not be excluded as a contributor.
  • Differential diagnostic errors or underreporting of Parkinson's disease were potential sources of bias.
  • The statistical tests were not adjusted for multiple comparisons.
  • Pesticide exposure could be a marker of other aspects of rural living rather than the actual cause.

Topics

Medical terms in this study, explained in our Lexicon: Relative Risk, confidence interval, Occupational Exposure.

Related studies

• Increased risk of lung cancer in pesticide-exposed male agricultural workers — E. Barthel (1981)
• Exposure to non-arsenic pesticides is associated with lymphoma among farmers in Spain — E. van Balen, R. Font, et al. (2006)
• Comparison of risks from outdoor and indoor exposure to toxic chemicals — L.A. Wallace (1991)
• Exposure to environmental chemicals and heavy metals, and risk of pancreatic cancer — S.O. Antwi, E.C. Eckert, et al. (2015)
• Pleuropulmonary fibrosis after long-term treatment with the dopamine agonist pergolide for Parkinson Disease — R. Tintner, P. Manian, et al. (2005)
• Inorganic particles of agricultural origin — K. Kay (1974)

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