14/09/2025
The role of environmental toxins in the development of autoimmune diseases is an area of growing scientific interest and concern. While genetic predisposition plays a key role in autoimmunity, increasing evidence suggests that environmental exposures may trigger, exacerbate or accelerate autoimmune processes in genetically susceptible individuals.
Now a large US government study has found a higher rheumatoid arthritis (RA) risk in women after exposure (through farm work or as farmers' wives) to certain common insecticides and fungicides, but not most herbicides.
"In sum, our findings provide robust evidence that some insecticides may contribute to risk of developing RA in women," the researchers wrote. "Further studies are warranted especially for widely used insecticides, such as malathion, carbaryl, and pyrethroids, given ongoing residential and public health uses such as mosquito control, and residential or personal uses such as permethrin-treated clothing."
This is not the first time that agricultural chemical exposure has been linked to RA risk. Such an association was found in one analysis from the Women's Health Initiative, involving household and garden products.
In the current study, participants in the Agricultural Health Study were recruited in North Carolina and Iowa during 1993-1997, including around 32,000 women who either worked directly on farms or were farmers' spouses. They completed detailed questionnaires, which included questions about contact with 50 pesticides, herbicides, and fungicides, at enrolment and at an initial follow-up conducted in 1999-2003. Additional follow-ups were performed periodically through 2021, with participants asked whether they had been diagnosed with RA or other conditions. The authors also reviewed participants' Medicare claims for RA diagnoses.
After excluding participants with insufficient data, the group compared 410 incident RA cases with 21,850 non-cases. "Ever use" of specific chemicals was counted in each of these groups. Associations between RA risk and individual chemicals were adjusted for age, state of residence, education level, smoking history, body mass index, and exposure to other "correlated" pesticides.
With these adjustments, the following pesticides had significant associations with incident RA, expressed as odds ratios (ORs):
• DDT: 1.89, 95% CI (confidence interval) 1.30-2.75
• Lindane: 1.97, 95% CI 1.12-3.47
• Coumaphos: 2.32, 95% CI 1.29-4.19
• Permethrin/pyrethroids on livestock: 1.76, 95% CI 1.16-2.69
Additionally, strong trends falling short of statistical significance were seen for malathion, carbofuran, and permethrin/pyrethroid insecticides on crops.
Among herbicides and fungicides, significant ORs were found for these products:
• Metribuzin (a herbicide): 2.74, 95% CI 1.67-4.48
• Captan: 1.78, 95% CI 1.13-2.83
• Metalaxyl: 2.49, 95% CI 1.49-4.16
Limitations to the current analysis included that pesticide exposure was self-reported and recorded only as "ever used" without quantification. Also, many individual pesticides had been used by only a handful of participants with incident RA.
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