The Rheumatic Dangers of Wildfire Smoke

As wildfires become more common, the smoke pollution they cause may be contributing to the risk of rheumatoid arthritis (RA) and RA-associated interstitial lung disease (ILD), recent research suggests.¹

The study in Arthritis & Rheumatology adds to a growing body of research that points to an association between air pollutants and RA and RA-ILD.

The researchers’ case-control analysis using healthcare data from the U.S. Veterans Affairs, as well as federal air pollution data, found that exposure to fire smoke particulate matter smaller than 2.5 microns (PM_2.5) is associated with RA-ILD. Exposure to nitrogen oxides (NO_x), ozone and particulate matter smaller than 10 microns (PM₁₀) is associated with incident RA risk, the paper notes.

“We were able to study almost 80,000 veterans across the U.S., and we found that increased fire smoke exposure was associated with both RA and RA-ILD, and other pollutants may also be associated with RA. These pollutants come from either the wildfires or fossil fuel combustion,” says lead author Vanessa L. Kronzer, MD, first author and assistant professor of medicine in the Division of Rheumatology, Mayo Clinic, Rochester, Minn.

The Study

Dr. Kronzer

Dr. Kronzer says the study arose from her involvement in Mayo Clinic’s long-established Rochester Epidemiology Project, which focuses on Olmsted County and a family vacation in an area affected by wildfire smoke. Dr. Kronzer and lead author Bryan England, MD—who also vacationed amid wildfire smoke—knew that respiratory inflammation is associated with RA in many forms. Inflammation triggers include military burn pits, smoking and occupational exposures. “It occurred to us that this smoke [may be] another inhaled irritant that could be associated with RA,” says Dr. Kronzer.

In their study, the researchers aimed to determine whether substances in fire smoke are associated with RA and RA-ILD. The researchers analyzed more than nine years of Veterans Affairs (VA) healthcare data on 9,701 patients with RA, including 531 with ILD, and 68,582 controls matched for age, sex and VA enrollment year. The researchers analyzed exposures to fire smoke PM_2.5, plus other pollutants. These included NO_x, ozone, overall PM_2.5, PM₁₀, and sulfur dioxide (SO₂). The researchers chose these pollutants because they are included in Environmental Protection Agency (EPA) air quality system ground pollutant monitoring data. Preliminary data suggested many of these pollutants may have an association, Dr. Kronzer explains.

The researchers determined fire smoke exposure from combining these EPA data with satellite-based smoke plume imagery from the National Oceanic and Atmospheric Administration Hazard Mapping System. The researchers overlapped these data sources to produce daily grids of smoke-related PM_2.5, non-smoke PM_2.5 and overall total PM_2.5 over the contiguous U.S. The researchers’ analysis also involved assigning daily concentrations of each pollutant to ZIP codes.