Exposure to traffic pollution and increased risk of rheumatoid arthritis

Background: Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease that affects approximately 1% of the adult population, and to date, genetic factors explain < 50% of the risk. Particulate air pollution, especially of traffic origin, has been linked to systemic inflammation in many studies.

Objectives: We examined the association of distance to road, a marker of traffic pollution exposure, and incidence of RA in a prospective cohort study.

Methods: We studied 90,297 U.S. women in the Nurses' Health Study. We used a geographic information system to determine distance to road at the residence in 2000 as a measure of traffic exposure. Using Cox proportional hazard models, we examined the association of distance to road and incident RA (1976-2004) with adjustment for a large number of potential confounders.

Results: In models adjusted for age, calendar year, race, cigarette smoking, parity, lactation, menopausal status and hormone use, oral contraceptive use, body mass index, physical activity, and census-tract-level median income and house value, we observed an elevated risk of RA [hazard ratio (HR) = 1.31; 95% confidence interval (CI), 0.98-1.74] in women living within 50 m of a road, compared with those women living 200 m or farther away. We also observed this association in analyses among nonsmokers (HR = 1.62; 95% CI, 1.04-2.52), nonsmokers with rheumatoid factor (RF)-negative RA (HR = 1.77; 95% CI, 0.93-3.38), and nonsmokers with RF-positive RA (HR = 1.51; 95% CI, 0.82-2.77). We saw no elevations in risk in women living 50-200 m from the road.

Conclusions: The observed association between exposure to traffic pollution and RA suggests that pollution from traffic in adulthood may be a newly identified environmental risk factor for RA.