Long-term exposure to air pollution linked to autoimmune disease risk, study finds

Long-term exposure to air pollution is linked to a heightened risk of autoimmune disease, particularly rheumatoid arthritis, and inflammatory bowel diseases, according to a major study of more than 80,000 adults.

The research provides further evidence of the health threat from tiny airborne pollutants, known as particulate matter (PM), arising from vehicle exhausts, burning of material, especially fossil fuels, and from industrial emissions.

Environmental air pollution from such sources usually triggers “adaptive immunity” – whereby the body reacts to a specific disease-causing threat. But sometimes this adaptive response misfires, prompting systemic inflammation, tissue damage, and ultimately autoimmune disease, the large study conducted by Italian scientists confirms.

Examples of autoimmune disease include rheumatoid arthritis, multiple sclerosis and the most common form of lupus as well as inflammatory bowel diseases such as ulcerative colitis.

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Both the global incidence and prevalence of these conditions have steadily increased over the past decade, including in Ireland, but the reasons for this are not entirely clear.

This study focussed on potential impact of particulates classified as PM10 and PM2.5, which above certain thresholds are considered harmful to human health. Air pollution has been associated with disruption of the immune system at a molecular level, but a possible link to autoimmune diseases has not been established.

The researchers mined the national Italian fracture risk database, and retrieved comprehensive medical information on 81,363 men and women submitted by more than 3,500 doctors between June 2016 and November 2020.

The findings are published in open access journal RMD Open – a BMJ publication.

Rheumatologist Dr Giovanni Adami of the University of Verona, who led the study, explained its significance: "We found that long-term exposure to air pollution was associated with higher risk of autoimmune diseases. In particular, exposure to particulate matter PM10 was associated with rheumatoid arthritis, while exposure to PM2.5 was associated with rheumatoid arthritis, connective tissue diseases and inflammatory bowel diseases."

On clinical implications, he said it underlined “individuals chronically exposed to high levels of air pollution might be at risk of developing autoimmune diseases”.

Women (92 per cent) with an average age of 65 figured most prominently in the study, while 17,866 (22 per cent) had at least one co-existing health condition. Almost 10,000 people (12 per cent) were diagnosed with an autoimmune disease between 2016 and 2020.

Each participant was linked to the nearest air quality monitoring station via their residential postcode – there are 617 such stations in Italy.

Exposure to PM2.5 was not associated with a heightened risk of an autoimmune disease diagnosis. But PM10 was associated with a 7 per cent heightened risk for every 10 micrograms per square metre (µg/m3) increase in levels after factoring in potentially influential factors.

Long-term exposure to PM10 above 30 µg/m3 and to PM2.5 above 20 µg/m3 were associated with a 12 per cent and 13 per cent higher risk of autoimmune disease, respectively.

Overall, long-term exposure to traffic and industrial air pollutants was associated with an approximately 40 per cent higher risk of rheumatoid arthritis, a 20 per cent higher risk of inflammatory bowel disease, and a 15 per cent higher risk of connective tissue diseases.

As this is an observational study, it cannot establish cause and researchers acknowledge limitations which might have affected their findings.

However, air pollution has already been linked to immune system abnormalities, and smoking, which shares some toxins with fossil fuel emissions, is a predisposing factor for rheumatoid arthritis, they underline.