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 (PM2.5) 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 PM2.5, 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 PM2.5 and PM10 for age below as compared to above 40 years. In conclusion, exposure to PM2.5, NO2 and EC increased risk of RA, with little influence from sex and some influence of age.