Other analyses of data have found environmental air pollution from sources such as car exhaust and factory output can trigger an inflammatory response in the body. What’s new about a study published in RMD Open is that it explored an association between long-term exposure to pollution and risk of autoimmune diseases, wrote Giovanni Adami, MD, of the University of Verona (Italy) and colleagues.
“Environmental air pollution, according to the World Health Organization, is a major risk to health and 99% of the population worldwide is living in places where recommendations for air quality are not met,” said Dr. Adami in an interview. The limited data on the precise role of air pollution on rheumatic diseases in particular prompted the study, he said.
To explore the potential link between air pollution exposure and autoimmune disease, the researchers reviewed medical information from 81,363 adults via a national medical database in Italy; the data were submitted between June 2016 and November 2020.
The average age of the study population was 65 years, and 92% were women; 22% had at least one coexisting health condition. Each study participant was linked to local environmental monitoring via their residential postcode.
The researchers obtained details about concentrations of particulate matter in the environment from the Italian Institute of Environmental Protection that included 617 monitoring stations in 110 Italian provinces. They focused on concentrations of 10 and 2.5 (PM10 and PM2.5).
Exposure thresholds of 30 mcg/m3 for PM10 and 20 mcg/m3 for PM2.5 are generally considered harmful to health, they noted. On average, the long-term exposure was 16 mcg/m3 for PM2.5 and 25 mcg/m3 for PM10 between 2013 and 2019.
Overall, 9,723 individuals (12%) were diagnosed with an autoimmune disease between 2016 and 2020.
Exposure to PM10 was associated with a 7% higher risk of diagnosis with any autoimmune disease for every 10 mcg/m3 increase in concentration, but no association appeared between PM2.5 exposure and increased risk of autoimmune diseases.
However, in an adjusted model, chronic exposure to PM10 above 30 mcg/m3 and to PM2.5 above 20 mcg/m3 were associated with a 12% and 13% higher risk, respectively, of any autoimmune disease.
Chronic exposure to high levels of PM10 was specifically associated with a higher risk of rheumatoid arthritis, but no other autoimmune diseases. Chronic exposure to high levels of PM2.5 was associated with a higher risk of rheumatoid arthritis, connective tissue diseases, and inflammatory bowel diseases.
In their discussion, the researchers noted that the smaller diameter of PM2.5 molecules fluctuate less in response to rain and other weather, compared with PM10 molecules, which might make them a more accurate predictor of exposure to chronic air pollution.
The study findings were limited by several factors including the observational design, which prohibits the establishment of cause, and a lack of data on the start of symptoms and dates of diagnoses for autoimmune diseases, the researchers noted. Other limitations include the high percentage of older women in the study, which may limit generalizability, and the inability to account for additional personal exposure to pollutants outside of the environmental exposure, they said.
However, the results were strengthened by the large sample size and wide geographic distribution with variable pollution exposure, they said.
“Unfortunately, we were not surprised at all,” by the findings, Dr. Adami said in an interview.
“The biological rationale underpinning our findings is strong. Nevertheless, the magnitude of the effect was overwhelming. In addition, we saw an effect even at threshold of exposure that is widely considered as safe,” Dr. Adami noted.
Clinicians have been taught to consider cigarette smoking or other lifestyle behaviors as major risk factors for the development of several autoimmune diseases, said Dr. Adami. “In the future, we probably should include air pollution exposure as a risk factor as well. Interestingly, there is also accumulating evidence linking acute exposure to environmental air pollution with flares of chronic arthritis,” he said.
“Our study could have direct societal and political consequences,” and might help direct policy makers’ decisions on addressing strategies aimed to reduce fossil emissions, he said. As for additional research, “we certainly need multination studies to confirm our results on a larger scale,” Dr. Adami emphasized. “In addition, it is time to take action and start designing interventions aimed to reduce acute and chronic exposure to air pollution in patients suffering from RMDs.”