Exposure to car exhaust and other airborne toxins has long been linked to a wide range of health problems, including heart and lung diseases as well as rheumatoid arthritis, an immune system disorder that causes debilitating swelling and pain in the joints.
For the new study, researchers examined medical records from more than 81,000 older adults treated by more than 3,500 doctors in Italy between June 2016 and November 2020. They also looked at air quality data from 617 monitoring stations across 110 Italian provinces to estimate levels of two types of so-called particulate matter: PM2.5, which is smaller than 2.5 micrometers in diameter and can include emissions from burning gasoline, oil, and wood; and PM10, which is 10 micrometers or less in diameter and includes everything in PM2.5 as well as dust from construction, agriculture, landfills, and wildfires.
During the study, 12 percent of the participants were diagnosed with an autoimmune disease.
Higher levels of air pollution exposure increased the odds of this happening. Each additional 10 micrograms per cubic meter (mcg/m3) of average PM10 levels was associated with a 7 percent greater autoimmune disease risk.
“People should be aware that being chronically exposed to air pollution can trigger their autoimmune system, as well as being a risk for cardiovascular and pulmonary diseases,” says the lead study author, Giovanni Adami, MD, PhD, a rheumatology researcher at the University of Verona in Italy.
“We have also evidence that acute exposure to high levels of air pollution can aggravate inflammatory rheumatic diseases, such as rheumatoid arthritis,” Dr. Adami says.
Average annual exposure levels of air pollution during the study period were 16 mcg/m3 for PM2.5 and 25 mcg/m3 for PM10, the study found. That’s below recommended limits set by the World Health Organization (WHO) of 25 mcg/m3 for PM2.5 and 20 mcg/m3 for PM10.
At and above these limits set by the WHO, people in the study had a 12 to 13 percent higher risk of developing autoimmune disorders, researchers reported March 15 in Rheumatic & Musculoskeletal Diseases.
When researchers examined individual autoimmune disorders, they found PM10 associated specifically with rheumatoid arthritis. PM2.5 was associated with rheumatoid arthritis, connective tissue diseases, and inflammatory bowel disease.
Air pollution exposure was associated with a 40 percent higher risk of rheumatoid arthritis, a 20 percent greater chance of inflammatory bowel disease, and a 15 percent larger risk of connective tissue disease.
The study wasn’t designed to prove whether or how air pollution might directly cause autoimmune conditions. It’s possible air pollution triggers a reaction in the body that’s supposed to help fight off disease-causing toxins, but misfires and instead causes inflammation and tissue damage that leads to autoimmune disease, Adami says.
Other limitations of the study include a lack of data on the timing of any autoimmune disease diagnoses and the absence of information on the cumulative duration or amount of air pollution exposure for individual participants. The study also included mostly older women who were part of a larger study on fracture risk after menopause, and the results may not be generalizable to other populations.
Even so, the study makes a strong case that air pollution can play a role in autoimmune diseases, says Luz Claudio, PhD, a professor of preventive medicine and public health at the Icahn School of Medicine at Mount Sinai in New York City.
“Air pollution is pervasive and affects many organs, not only the lungs,” says Dr. Claudio, who wasn’t involved in the study.
While it’s not possible for people to avoid breathing polluted air, they can advocate for better environmental regulations, Claudio says. And they can push for better monitoring so they know how safe the air is in their own community.
“Having a good surveillance system in areas where air pollution is highest is a very good idea, particularly for susceptible individuals,” Claudio says. “On days with high pollution levels, people can try to avoid outdoor activities when possible.”