Dirty air may trigger painful rheumatoid arthritis flares

Air pollution may make rheumatoid arthritis more active and increase the likelihood of painful flare-ups, according to a new study. The strongest connection involved fine particulate matter found in dust, soot, and smoke (PM2.5).

Published in the Annals of the Rheumatic Diseases (ARD), The EULAR Journal, by Elsevier, the findings suggest that air quality may be an important consideration for both healthcare professionals treating rheumatoid arthritis and policymakers working to protect public health.

Environmental Factors in Rheumatoid Arthritis

Rheumatoid arthritis, commonly known as RA, is a chronic autoimmune condition that causes inflammation and damage in the joints. It can also produce widespread symptoms that affect other areas of the body.

The disease affects an estimated 0.5% to 1% of adults worldwide. Its development is influenced by a combination of genetics, changes in immune function, and environmental exposures. Some of these environmental influences may contribute not only to the initial development of RA, but also to worsening symptoms after the disease has been diagnosed.

Importantly, several environmental risk factors can potentially be modified. Smoking is already recognized as a major risk factor. Researchers have also examined the possible effects of temperature, humidity, silica, and other pollutants.

Earlier population studies found that exposure to polluted air was associated with a greater likelihood of developing RA. Researchers in South Korea wanted to determine whether air pollution could also affect disease activity and trigger flares in people who already had the condition. They also investigated the biological processes that might explain such a connection.

In an accompanying editorial Jeffrey A. Sparks, MD, MMSc, Division of Rheumatology, Inflammation, and Immunity, Mass General Brigham / Brigham and Women's Hospital, and Harvard Medical School, comments, "This is one of the largest studies to use robust methods to link air pollutants with RA disease activity. Considering rising levels of air pollutants, these results have significant clinical, biologic, and public health implications. They also further reinforce that inhalants may have broad implications for risk and progression of RA and perhaps other autoimmune diseases. From a clinical perspective, this may offer avenues to lower the risk of RA flares by avoiding air with poor quality and provide some potential explanation for otherwise idiosyncratic RA flares."

Tracking Air Pollution and Arthritis Flares

The prospective cohort study followed 1,070 people with RA at a major medical center in South Korea. Over four years (2021-2024), the researchers collected information from 12,583 outpatient visits conducted under real-world clinical conditions.

To estimate each patient's exposure, the team examined monthly levels of six common air pollutants (sulfur dioxide, SO2; nitrogen dioxide, NO2; ozone, O3; carbon monoxide, CO; particulate matter with a diameter of 10 µm, PM10; and particulate matter with a diameter of 2.5 µm, PM2.5). These measurements were then compared with disease activity and flare outcomes recorded during each visit.

The analysis accounted for a wide range of factors that could influence the results. These included patient demographics, serologic status (the presence of specific antibodies typical for RA in the blood), medication use, socioeconomic conditions, and weather-related variables.

The researchers also performed a sensitivity analysis designed to reduce the influence of factors that remained constant over time and to limit the possibility that disease activity itself affected the pollution measurements used in the monthly analysis. For this part of the research, they used a case crossover design based on daily pollutant concentrations before each appointment. Conditional logistic regression allowed them to compare changes within individual patients.

PM2.5 Emerges as the Strongest Factor

"Our study found that higher PM2.5 concentration was associated with increased disease activity and flare risk, notably prolonged exposure to elevated PM2.5 over more than two weeks," explains lead investigator Eun Bong Lee, MD, PhD, Division of Rheumatology, Department of Internal Medicine, Seoul National University College of Medicine, and Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Republic of Korea.

Among the pollutants studied, PM2.5 appeared to be the main contributor associated with increased RA activity.

These particles are extremely small, even smaller than red blood cells. After being inhaled, they can pass from the lungs into the bloodstream and travel to organs throughout the body.

Researchers say the particles may stimulate excessive production of reactive oxygen species, which are harmful molecules that can place cells under stress. This process may damage DNA and activate inflammatory responses in different organs, potentially contributing to greater RA activity and more frequent flares.

Air Quality Could Affect RA Management

Dr. Lee concludes, "Our study has important implications for public health policy making. While further studies are warranted to determine whether improving air quality can reduce disease activity in RA patients, we would recommend these patients avoid prolonged exposure to poor air quality, particularly high PM2.5 levels."

The researchers emphasized that additional studies are needed to determine whether reducing pollution exposure or improving air quality can directly lower disease activity in people with RA. Even so, the results suggest that limiting prolonged exposure during periods of poor air quality may be a practical precaution.

ARD Editor-in-Chief Josef Smolen, MD, from the Medical University of Vienna, adds: "As always, this paper underwent thorough peer review, and it was nice to learn that all reviewers agreed on the importance and interest of these findings. Nevertheless, we should be aware that the observations pertain to the studied Korean population, with a specific genetic background and under specific environmental circumstances. Whether these data hold true in other regions of the world should be a focus of future investigations. However, it is an excellent starting point for our better understanding of factors that may play a role in influencing disease activity and therapeutic responses of patients with RA. And: it is an important wake-up call: the environment is likely an essential contributor to pain and inflammation in the patients for whom we care."

Reporting from ScienceDaily contributed to this story.