Objective Environmental factors may play a role in the development of rheumatoid arthritis (RA). We examined whether long-term exposures to air pollution were associated with the risk of RA in the Swedish Epidemiological Investigation of Rheumatoid Arthritis Study.

Methods We studied 1497 incident RA cases and 2536 controls. Local levels of particulate matter (PM₁₀) and gaseous pollutants (sulphur dioxide (SO₂) and nitrogen dioxide (NO₂)) from traffic and home heating were predicted for all residential addresses. We examined the association of an IQR increase (2 µg/m³ for PM₁₀, 8 µg/m³ for SO₂ and 9 µg/m³ for NO₂) in each pollutant at different time points before symptom onset and average exposure with the risk of all RA and the risk of the rheumatoid factor and anti-citrullinated protein antibody (ACPA) RA phenotypes.

Results There was no evidence of an increased risk of RA with PM₁₀. Total RA risks were modestly elevated for the gaseous pollutants, but were not statistically significant after adjustment for smoking and education (OR 1.18, 95% CI 0.97 to 1.43 and OR 1.09, 95% CI 0.99 to 1.19 for SO₂ and NO₂ in the 10th year before onset). Stronger elevated risks were observed for individuals with less than a university education and with the ACPA-negative RA phenotype.

Conclusions No consistent overall associations between air pollution in the Stockholm area and the risk of RA were observed. However, there was a suggestion of increased risks of RA incidence with increases in NO₂ from local traffic and SO₂ from home heating sources with stronger associations for the ACPA-negative phenotype.