Air Pollution May Increase the Risk of RA & RA-Associated ILD

With the number of wildfires in the U.S. increasing, the corresponding higher levels of particulate matter (PM)—the main pollutant in fire smoke—in the environment may be negatively affecting human health. Prior research has found that PM levels less than 2.5 μm (PM_2.5) may be associated with anti-citrullinated protein antibody production, a hallmark of rheumatoid arthritis (RA), as well as the onset of diabetes, Parkinson’s and other conditions. Thus, fire smoke may be a risk factor for RA.

Past research has indicated that other air pollutants, such as carbon monoxide, nitrogen oxides, ozone, PM₁₀ and sulfur dioxide, may also increase the risk of RA, interstitial lung abnormalities and idiopathic pulmonary fibrosis.

In a patient-control study, Kronzer et al. sought to better determine the associations between fire smoke and other pollutants with incident RA and RA-associated interstitial lung disease (ILD), as well as identify the timing of the associations.

Methods

Using U.S. Veterans Affairs patient data from Oct. 1, 2009, to Dec. 31, 2018, the researchers identified patients with incident RA and RA-associated ILD using validated algorithms, matching each patient to 10 or fewer controls based on age, sex and VA enrollment year.

Next, researchers obtained nationwide pollutant monitoring data from the U.S. Environmental Protection Agency, including data on fire smoke PM_2.5, carbon monoxide, nitrogen oxides, ozone, overall PM_2.5, PM₁₀ and sulfur dioxide, at least one year before the index date—defined as the time of RA diagnosis.

The study used conditional logistic regression models to estimate the adjusted odds ratios (aORs) with 95% confidence intervals (CI) for incident RA and RA-associated ILD, adjusted for confounders.

The Results

The study identified 9,701 patients with incident RA (mean age 65 years, 86% male), including 531 patients with RA-associated ILD (mean age 69 years, 91% male) and 68,852 matched controls. The first key finding was that exposure to high levels of PM_2.5 from fire smoke was associated with RA-associated ILD (aOR 1.98; 95% CI 1.08–3.62, per 1 μg/m3), but not with overall RA (aOR 1.07; 95% CI 0.92–1.23). However, the stratified analyses showed an association between exposure to high levels of PM_2.5 and RA in the one to five years before RA diagnosis.

The study’s second key finding was that high levels of other pollutants, such as nitrogen oxide, were associated with incident RA overall (aOR 1.16; 95% CI 1.06–1.27). Additionally, ozone (aOR 1.19, 95% CI 1.06–1.34) and PM₁₀ (aOR 1.25, 95% CI 1.10–1.43) levels were associated with seronegative RA. The other pollutants studied, including carbon monoxide, overall PM_2.5 and sulfur dioxide, were not associated—or even inversely associated—with RA and RA-associated ILD.

For complete details, including source material, refer to the full study.   

Excerpted and adapted from:

Kronzer VL, Yang Y, Roul P, et al. Associations of fire smoke and other pollutants with incident rheumatoid arthritis and rheumatoid arthritis-associated interstitial lung disease. Arthritis Rheumatol. 2025 Jun;77(6).