Purpose: Farming has been associated with increased risk of rheumatoid arthritis (RA) in some studies, but specific causes have not been identified. We studied risk factors for RA in the Agricultural Health Study, a cohort of over 57,000 licensed pesticide applicators and their spouses.
Methods: We used a nested case-control design, limited to female participants. Physician-confirmed cases (n = 135) were matched to five controls each (n = 675) by birth date. We used logistic regression, adjusting for birth date and state to examine associations, as estimated by odds ratios (OR) and 95% confidence intervals (CI).
Results: Risk of RA was not associated with mixing or applying pesticides overall or with any pesticide class, nor did it vary by number of days or years of use. Certain pesticides were associated with small nonsignificantly increased risks, including lindane (OR = 1.8, 95% CI: 0.6-5.0). RA risk was associated with welding (OR = 2.1, 95% CI: 0.8-5.4), albeit imprecisely, but not with solvents or sunlight.
Conclusions: We did not identify any strong risk factors for RA. Because of the severe disability associated with this relatively common disease, further investigation into causes is warranted both in the Agricultural Health Study and elsewhere.