Long-Term Residential Ambient Air Pollution and Rheumatoid Arthritis: A Systematic Review

There has been increasing interest regarding the effects of air pollution on the risk of rheumatoid arthritis. Unfortunately, epidemiologic research on air pollution effects remains scant and offers conflicting results. This study aimed to systematically review the epidemiologic literature on RA morbidity due to long-term residential air pollution. The authors independently carried out searches in MEDLINE and EMBASE through June 2015 (1974 - 2015). The searches were limited to English, Spanish and Russian. To complement the search strategy, authors and experts in the field were contacted, and hand-searches were carried out for articles included in reference lists. Peer-reviewed epidemiologic studies were eligible only if they explored the risk for RA in adults associated with air pollution exposure. Studies were omitted if they relied on self-report alone, experimental studies, short-term effects of air pollution, juvenile arthritis, or other autoimmune rheumatic diseases. Two authors independently extracted information about study characteristics. The study’s quality was assessed with the Newcastle-Ottawa scale. Four relevant papers were included in a qualitative synthesis. Two studies showed significantly higher risks for RA in people living within 50 m of a heavy traffic road. No firm conclusions could be made for particulate matter. In one study, NO2 was associated with seronegative RA among smokers. The risk for SO2 was significant in one study. In the only relevant study, O3 was linked to RA. Proximity to road traffic might be a risk factor for RA as there are suspected effects associated with NO2 and SO2. Overall, the available evidence is too preliminary and scarce to draw firm conclusions. However, the results indicate the feasibility of further studies elucidating on the relationship between air pollution and RA.