Associations between pesticide use and rheumatoid arthritis among older farmers in the Agricultural Health Study

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Pesticides and farming have been associated with increased rheumatoid arthritis (RA) risk, but the role of specific pesticides remains unknown. We examined RA risk among licensed pesticide applicators (97% white male farmers), from North Carolina and Iowa, in the Agricultural Health Study, in relation to lifetime use of 45 pesticides reported at enrollment (1993–1997, updated 1999–2003). In 22,642 applicators ages ≥ 67 years with ≥ 24 months Fee for Service Medicare data (1999–2016), we identified 161 (0.7%) incident cases with ≥ 2 RA claims (including ≥ 1 by a rheumatologist), ≥ 30 days apart, after ≥ 12 months without RA claims. Relative risks (RR) and 95% Confidence Intervals (CI) were calculated using log-binomial models adjusted for age, state, education, smoking, and correlated pesticides. Risk was elevated (RR > 1.5 or lower CI > 0.95) for use of nine pesticides: four insecticides [malathion (RR = 1.77;95%CI = 1.14–2.73), phorate (1.40;0.96–2.04), carbaryl (1.65;1.10–2.46), carbofuran (1.41;0.99–2.01)], four herbicides [alachlor (RR = 1.40;95%CI 0.99–1.98), metolachlor (1.57;1.11–2.23), S-Ethyl dipropylthiocarbamate (1.57;1.00-2.44), metribuzin (1.45; 1.01, 2.08)], and one fungicide [benomyl (1.56;0.99–2.44)]. Exposure-response was seen for greater intensity-weighted lifetime days use of malathion and carbofuran (p-trends = 0.03 and 0.05). Some specific pesticides, including several currently approved and commonly used in agricultural, public health, or residential settings may increase RA risk among older adults.