Air pollution and risk of rheumatoid arthritis – A Danish register-based cohort study

This study examined the association between ambient air pollution and risk of rheumatoid arthritis (RA). Individuals born 1960-1999 from the nationwide Danish Occupational Cohort with eXposure data were linked to modeled exposure at the home address(es) and RA hospital diagnoses (N = 2,092,596). Recent and 10-years cumulative exposure to particles ≤ 2.5 (PM_2.5) and ≤ 10 µm (PM₁₀), nitrogen oxide (NO₂) and elemental carbon (EC) were subdivided into quartiles, and risk of incident RA (1997-2018) were calculated using Poisson regression analyses. Recent and cumulative exposure to PM_2.5, NO₂ and EC increased risk of RA, for all quartiles compared to the lowest quartile, but without a clear exposure-response relationship. Analyses stratified on sex generally showed similar trends, yet small differences were seen for PM2.5 and EC (differences between IRR for men and women in model 2: PM2.5 0.03-0.19, and EC 0.05-0.14). Higher risks were indicated for exposure to PM_2.5 and PM₁₀ for age below as compared to above 40 years. In conclusion, exposure to PM_2.5, NO₂ and EC increased risk of RA, with little influence from sex and some influence of age.