Researchers have found in a new study that persistent exposure to certain insecticides, particularly organochlorine pesticides, is associated with an increased risk of developing rheumatoid arthritis among women, according to a study published in Arthritis & Rheumatology. Rheumatoid arthritis is a systemic autoimmune disease that features inflammation of the joints, resulting in pain, stiffness, and possible damage to the joints. While genetic susceptibility plays an important role, environmental causes like smoking and exposure to chemicals have increasingly been shown to contribute to disease development.
The study involved 32,126 female spouses of licensed pesticide applicators who were enrolled in the Agricultural Health Study between 1993 and 1997 in Iowa and North Carolina. Incident RA cases were ascertained from follow-up questionnaires between 1999 and 2021, and confirmed by medical records, medication history, or Medicare claims data (1999–2016).
The RA-free participants did not have RA diagnosed or any related Medicare claims. Following exclusion of those with missing covariate data, analyses were performed on 410 confirmed RA cases and 21,850 non-cases. Investigators tested associations between RA and pesticide exposure with adjusted odds ratios (OR) and 95% confidence intervals (CI) for potentially confounding factors like age, state, education, pack-years of smoking, body mass index (BMI), and related pesticide exposures (rho > 0.35).
Results
A high risk association was observed between RA and exposure to various classes of fungicides and insecticides.
Women currently using organochlorine insecticides like DDT (OR 1.89; 95% CI, 1.30–2.75) and lindane (OR 1.97; 95% CI, 1.12–3.47) had increased odds of developing RA among non-users.
Among organophosphate insecticides, coumaphos (OR 2.32; 95% CI, 1.29–4.19) had a particularly significant association, with malathion (OR 1.21; 95% CI, 0.91–1.62) having a modest but non-significant risk increase.
The carbamate insecticide carbofuran (OR 1.87; 95% CI, 0.97–3.63) also had an association with increased risk.
Exposure to pyrethroid insecticides or permethrin, frequently applied to crops or livestock, was positively linked with increased RA risk when applied to crops (OR 1.56; 95% CI, 0.92–2.64) and livestock (OR 1.69; 95% CI, 1.07–2.68).
No strong associations were noted for herbicides, with the exception of metribuzin (OR 1.88; 95% CI, 0.94–3.79).
Two fungicides, captan (OR 1.78; 95% CI, 1.13–2.83) and metalaxyl (OR 2.49; 95% CI, 1.41–4.40), were also significantly related to incident RA.
The findings imply that environmental and occupational exposure to pesticides contributes to autoimmune disease pathogenesis and suggest a need for tighter regulation of pesticides, reduction in exposure, and additional studies of the biological mechanisms connecting pesticide application and autoimmune disease.
Reference:
Parks, C. G., Leyzarovich, D., Hamra, G. B., Costenbader, K. H., Chen, D., Hofmann, J. N., Beane Freeman, L. E., & Sandler, D. P. (2025). Associations of specific pesticides and incident rheumatoid arthritis among female spouses in the Agricultural Health Study. Arthritis & Rheumatology, art.43318. https://doi.org/10.1002/art.43318
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