Long-term exposure to air pollution can increase the risk of autoimmune disease, research has found.
Exposure to particulates has already been linked to strokes, brain cancer, miscarriage and mental health problems. A global review, published in 2019, concluded that almost every cell in the body could be affected by dirty air.
Now researchers at the University of Verona have found that long-term exposure to high levels of air pollution was associated with an approximately 40% higher risk of rheumatoid arthritis, a 20% higher risk of inflammatory bowel disease such as Crohn’s and ulcerative colitis, and a 15% higher risk of connective tissue diseases, such as lupus.
The study, published in the journal RMD Open, took comprehensive medical information about 81,363 men and women on an Italian database monitoring risk of fractures between June 2016 and November 2020. About 12% were diagnosed with an autoimmune disease during this period.
Each patient was linked to the nearest air quality monitoring station via their residential postcode.
The study analyzed average long-term exposure to fine particulate matter (known as PM10 and PM2.5), which is produced by sources such as vehicles and power stations. Concentration levels of 30µg/m3 for PM10 and 20µg/m3 for PM2.5 are the thresholds generally considered harmful to human health.
The study concluded that overall, long-term exposure to particulates above these levels was associated with, respectively, a 12% and 13% higher risk of developing an autoimmune disease.
Felicity Gavins, the director of the Center for Inflammation Research and Translational Medicine at Brunel University London, said: “This study further supports the mounting evidence suggesting a link between air pollution exposure and immune-mediated diseases.”
But she cautioned against inferring that dirty air caused these conditions. “Whether air pollution exposure specifically causes autoimmune diseases remains controversial, although there is no doubt that there is a link.”
She also said more research was needed to ascertain why some areas of Italy had seen heightened growth in autoimmune conditions, and to look at the impact of passive smoking on the findings.
The researchers acknowledge their findings do not prove a causal link and that other factors may be at play, including lack of information on when autoimmune disease symptoms began, or that air quality monitoring might not reflect personal exposure to pollutants, and that the findings might not be more widely applicable because study participants largely understood older women at risk of fractures.
But air pollution has already been linked to immune system abnormalities, and smoking, which shares some toxins with fossil fuel emissions, was a predisposing factor for rheumatoid arthritis, said Dr Giovanni Adami, one of the report’s authors and a rheumatologist at the University of Verona .
“The World Health Organization has recently identified air pollution as one of the greatest environmental risks to health,” he said. “Our study provides new real-life evidence on the link between autoimmune diseases and air pollution exposure. In addition, there is a strong biological rationale underpinning our findings. However, a causal relationship is hard to prove. Indeed, it is unlikely that randomized controlled studies could be conducted on such topic.”