Air Pollution a Key Factor in Inflammatory Arthritis Development

Two abstracts presented by Dr Giovanni Adami at the 2022 EULAR Congress looked at the issue of environmental exposures and their role in disease development.

Particulate matter (PM) is defined as everything in the air that is not a gas. PM includes a variety of chemicals and materials, some of which can be toxic. Data from over 80,000 people in a retrospective observational study in Italy found a positive association between PM levels measured at local air-quality stations and the risk of autoimmune diseases. In fact, every 10 µg/m3 increase in PM10 concentration was associated with an incremental 7% risk of having autoimmune disease.

Exposure to PM10 above 30 µg/m3 and PM2.5 above 20 µg/m3 was associated with 12% and 13% higher risks of autoimmune disease, respectively. When broken down by individual diseases, exposure to PM10 was associated with an increased risk of rheumatoid arthritis (RA) but no other autoimmune diseases, whereas exposure to high levels of PM2.5 was associated with an increased risk of RA and inflammatory bowel disease. Overall, chronic exposure to particulate air pollution above the threshold for human protection was associated with a 10% higher risk of developing immune-mediated diseases.

The same group looked at the association between long-term exposure to PM and osteoporosis in almost 60,000 women at high risk of fracture. The results showed that exposure to PM2.5 was negatively associated with low bone mass at the top of the thigh bone and lumbar spine. Chronic exposure above 25 μg/m³ for PM2.5 and 30 μg/m³ for PM10 was associated with a 16% and 15% higher risk of having osteoporotic bone mass scores at any site. The researchers concluded that long-term exposure to air pollution was associated with higher risk of osteoporosis.

Previous studies have shown that breathing in crystalline silica is associated with the development of RA – but this research has historically focused on professional exposures and on male workers. Since substantial amounts of this pollutant are present in other environments, Dr Johanna Sigaux and colleagues set out to identify the main sources of exposure to crystalline silica in a group of RA patients regardless of their professional activity, and to assess the association between silica exposure and disease features.

The results showed that in women with RA, the main sources of crystalline silica exposure were cleaning activities. For example, handling dusty clothes or talcum powder. Women involved in these activities had higher exposure compared to people in the general population. Across the whole series of RA patients, high silica exposure was independently associated with lung abnormalities such as interstitial lung disease and mediastinal lymphadenopathy.

The study findings suggest that cleaning activities are underestimated sources of crystalline silica exposure that are overrepresented in women with RA compared to the general population, and may contribute to the pathogenesis of the disease.

Reference: Presented at the 2022 EULAR Congress.

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