Objectives Farming has been associated with rheumatoid arthritis (RA). Some studies have evaluated the effects of pesticides, but other agricultural exposures may also affect immune response.
Methods We investigated non-pesticide agricultural exposures in relation to RA in licensed pesticide applicators (n=27 175, mostly male farmers) and their spouses (n=22 231) in the Agricultural Health Study (AHS) cohort (1993–1997) who completed at least one follow-up survey through 2015. Incident RA cases (n=229 applicators and 249 spouses) were identified based on self-report confirmed by use of disease-modifying antirheumatic drugs or medical records. Hazard Ratios (HRs) and 95% Confidence Intervals (CIs) were estimated by Cox proportional hazard models adjusting for applicator status, state, smoking, education and specific pesticide use, allowing estimates to vary by median age when hazards assumptions were not met.
Results Overall, RA was associated with regularly applying chemical fertilisers (HR=1.50; 95% CI 1.11 to 2.02), using non-gasoline solvents (HR=1.40; 95% CI 1.09 to 1.80), and painting (HR=1.26; 95% CI 1.00 to 1.59). In older applicators (>62 years), RA was associated with driving combines (HR=2.46; 95% CI 1.05 to 5.78) and milking cows (HR=2.56; 95% CI 1.01 to 6.53). In younger participants (≤62 years), RA was inversely associated with raising animals as well as crops (HR=0.68; 95% CI 0.51 to 0.89 vs crops only). Associations with specific crops varied by age: some (eg, hay) were inversely associated with RA in younger participants, while others (eg, alfalfa) were associated with RA in older participants.
Conclusion These findings suggest several agricultural tasks and exposures may contribute to development of RA.
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Contributors All contributors meet the criteria for authorship.
Funding This work was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences (Z01-ES049030) and National Cancer Institute (Z01-CP010119). AM was funded by Coordination for the Improvement of Higher Education Personnel (CAPES), Brazil (grant no. 2478/2015-03).
Competing interests None declared.
Patient consent Not required.
Ethics approval This study was approved by the relevant institutional review boards.
Provenance and peer review Not commissioned; externally peer reviewed.