Long-term exposure to air pollution is associated with an increased risk of autoimmune disease, particularly rheumatoid arthritis, connective tissue and inflammatory bowel diseases, according to an on observational study.
The team of researchers in Italy noted that environmental air pollution from vehicle exhaust and industrial output can trigger adaptive immunity whereby the body reacts to a specific disease-causing entity.
However, sometimes this adaptive response misfires, prompting systemic inflammation, tissue damage, and ultimately autoimmune disease, they said.
Examples of autoimmune disease include rheumatoid arthritis, inflammatory bowel diseases such as ulcerative colitis, connective tissue disease such as osteoarthritis, and multiple sclerosis.
The study, published in the journal RMD Open, mined the national Italian fracture risk database (DeFRA).
It retrieved comprehensive medical information on 81,363 men and women submitted by over 3500 doctors between June 2016 and November 2020.
Most were women (92 per cent) with an average age of 65, and 17,866 (22 per cent) had at least one co-existing health condition.
The researchers were particularly interested in the potential impact of particulate matter -- PM10 and PM2.5.
Levels of 30 microgrammes per cubic metre (µg/m3) for PM10 and 20µg/m3 for PM2.5 are the thresholds generally considered harmful to human health.
About 9,723 people (12 per cent) were diagnosed with an autoimmune disease between 2016 and 2020.
Information on air quality was obtained from 617 monitoring stations in 110 Italian provinces.
Average long term exposure between 2013 and 2019 was 16 µg/m3 for PM2.5 and 25 µg/m3 for PM10.
The study found that exposure to PM2.5 was not associated with a heightened risk of an autoimmune disease diagnosis.
However, PM10 was associated with a 7 per cent heightened risk for every 10 µg/m3 increase in levels, after accounting for potentially influential factors, the researchers said.
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, they said.
The researchers found that long term exposure to PM10 was associated with an increased risk of rheumatoid arthritis, while long term exposure to PM2.5 was linked with a heightened risk of rheumatoid arthritis, connective tissue diseases, and inflammatory bowel diseases.
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, they said.
The researchers noted that the study is observational in nature, and as such, cannot establish cause.
They also acknowledge several limitations which might have affected their findings.
These include the lack of information on the dates of diagnosis and start of autoimmune disease symptoms, and that air quality monitoring might not reflect personal exposure to pollutants.
However, they explained that 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.
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