Effects of air pollution on disease activity in patients with rheumatoid arthritis

This study aimed to evaluate the associations of air pollution with disease activity and flare rate in patients with rheumatoid arthritis (RA).

This prospective cohort study included patients with RA who were treated at a tertiary medical centre in South Korea between January 2021 and December 2024. Air pollution exposure was estimated using monthly mean concentrations of 6 air pollutants (sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide, particulate matter [PM]₁₀, and PM_2.5). Disease activity and flares were recorded longitudinally at each outpatient visit. Associations between air pollution and RA disease activity or flare were analysed using linear and logistic generalised estimating equations, adjusting for demographic characteristics, serologic status, medication use, socioeconomic factors, and meteorological variables. As a sensitivity analysis, a case-crossover design using daily air pollutant concentrations preceding each visit was applied, with conditional logistic regression to assess within the same patient.

A total of 12,583 outpatient visits from 1070 patients were analysed. Among 6 pollutants, PM_2.5 was significantly associated with an increased risk of flare (adjusted odds ratio [OR]: 1.113 [95% CI: 1.017-1.218]) and with higher Disease Activity Score based on 28 joints (DAS28) with C-reactive protein (CRP), Clinical Disease Activity Index, 28-tender joint count, and 28-swollen joint count. In addition, the association between PM_2.5 and DAS28-CRP was more pronounced among women and nonsmokers. In the case-crossover analysis, prolonged cumulative exposure to PM_2.5 over >2 weeks was associated with an increased risk of RA flare.

Exposure to air pollutants, particularly PM_2.5, was associated with increased RA disease activity and flare risk. Further studies are warranted to determine whether improving air quality can reduce disease activity in patients with RA.