Ambient air pollution exposures and risk of rheumatoid arthritis

Objective Environmental factors may play a role in the development of rheumatoid arthritis (RA). We previously observed increased RA risk among women living closer to major roads (a source of air pollution). Herein, we examined whether long-term exposures to specific air pollutants were associated with RA risk among women in the Nurses' Health Study (NHS). Methods The NHS is a large US cohort of female nurses followed up prospectively every 2 years since 1976. We studied 111,425 NHS participants with information on air pollution exposures as well as data concerning other lifestyle and behavioral exposures and disease outcomes. Outdoor levels of different size fractions of particulate matter (PM₁₀ and PM_2.5) and gaseous pollutants (SO₂ and NO₂) were predicted for all available residential addresses using monitoring data from the US Environmental Protection Agency. We examined the association of time-varying exposures 6 and 10 years before each questionnaire cycle and cumulative average exposure with the risk of RA, seronegative (rheumatoid factor and anti-citrullinated peptide antibody negative) RA, and seropositive RA. Results Over the 3,019,424 person-years of followup, 858 incident RA cases were validated by medical record review by 2 board-certified rheumatologists. Overall, we found no evidence of increased risk of RA, seronegative RA, or seropositive RA with exposure to the different pollutants and little evidence of effect modification by socioeconomic status or smoking status, geographic region, or calendar period. Conclusion In this group of socioeconomically advantaged middle-aged and elderly women, adult exposures to air pollution were not associated with an increased RA risk.