Exposure to DDT, other pesticides exhibits ‘strong’ risk for rheumatoid arthritis
WASHINGTON — Exposure to specific pesticides, including DDT, demonstrates “strong and significant” risks for rheumatoid arthritis among the female spouses of pesticide applicators, according to a study presented at ACR Convergence 2024.
“Understanding whether certain pesticides play a role in RA may help us better understand the role of the environment in the development of the disease,” Christine Parks, PhD, an investigator in the epidemiology branch at the NIH National Institute of Environmental Health Sciences, in Durham, North Carolina, told Healio.
“Although smoking is the best-known environmental risk factor for RA, occupational risk factors have been identified, such as respirable exposure to crystalline silica,” she added. “Knowing these risk factors may help to identify patients at risk in clinical settings or provide clues for future prevention strategies.”
To examine the connections between pesticides and systemic autoimmune rheumatic diseases, Parks and colleagues analyzed data from the Agricultural Health Study cohort. Since RA is more common among women, the researchers focused on data from the female spouses of licensed pesticide applicators, Parks said. After a previous analysis found associations between RA and various pesticides, including DDT, the current analysis included more cases, updated exposure data and 10 additional years of follow-up.
Participants were enrolled between 1993 and 1997, in North Carolina and Iowa, and responded to up to four study questionnaires through 2021. Self-reported RA in the questionnaires was confirmed via medical records, Medicare claims data and the use of disease-modifying anti-rheumatic drugs. In a complete case analysis, logistic regression was used to assess the risks for RA, adjusted for demographic factors, BMI and pack-years of smoking among 410 incident cases of RA (median age at diagnosis, 62 years) and 22,260 non-cases.
According to the researchers, the adjusted models demonstrated increased risks for RA for several insecticides: DDT (OR = 1.91; 95% CI, 1.31-2.77), lindane (OR = 1.99; 95% CI, 1.13-3.51), coumaphos (OR = 2.32; 95% CI, 1.29-4.19) and permethrin use on livestock (OR = 1.76; 95% CI, 1.16-2.69). Other strong associations were seen for the fungicides captan (OR = 1.78; 95% CI, 1.13-2.83) and metalaxyl (OR = 2.49; 95% CI, 1.49-4.16).
The association of RA with DDT, replicating findings in the previous analysis, was “reassuring,” Parks said. However, there were no associations reported with the fungicides maneb/mancozeb, as previously observed.
“This is likely due to strong correlations of maneb/mancozeb with metalaxyl use, which was one of the strongest associations in the current analysis,” Parks said. “Having the larger sample size enabled us to investigate more pesticides — 32, compared with 15 in the earlier study — and to adjust for correlated use of the different types of pesticides women may have used over time.”
Additional analyses are needed to untangle “which risk factors uniquely contribute to disease risk, but also to explore risk in relation to the bigger picture of pesticides and other exposures among farm women,” she added.
The potential risks from pesticides may extend beyond work in agriculture, according to Parks.
“Although farming is an uncommon occupation and agricultural settings may convey higher exposures than in the general population, pesticide exposures are widespread, for example, due to uses in homes and gardens, offices, various public landscapes — eg, parks or golf courses — as well as uses in public health or clinical settings,” she said.
“According to the U.S. Geological Service, over a billion pounds of pesticides are used in the United States each year, much of which supports our food system to some extent, leading to contamination at lower levels in the water and foods consumed in the general population,” Parks added. “Effects on autoimmune diseases at these lower levels are not known but warrant further research.”
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Parks C. Abstract #2590. Presented at: ACR Convergence 2024; Nov. 14-19, 2024; Washington, D.C.
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