Exposure to SO2 and NO2 may increase risk for early-onset UC and CD

MedWire News: Residential exposure to sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) may increase the risk for developing early-onset ulcerative colitis (UC) or Crohn's disease (CD), say Canadian researchers.

However, they also found that air pollution exposure, overall, did not increase the incidence of associated with the incidence of inflammatory bowel disease (IBD).

Using the database of the UK health improvement network (THIN), Gilaad Kaplan (University of Calgary, Alberta) and colleagues selected 367 and 591 incident CD and UC cases, respectively, with a corresponding mean age of 43 and 49 years.

They then assessed whether these patients were more likely to live in areas of higher ambient concentrations of NO₂, SO₂, and particulate matter <10 µm (PM₁₀) than 4795 age- and gender-matched controls.

Postcode-based environmental indicators are included in the THIN database, and they were used to select the correct SO₂, NO₂, and PM₁₀ readings for each participant's residential area.

They found that overall, SO₂, NO₂, and PM₁₀ were not associated with IBD risk.

However, when stratified by age, individuals aged 23 years or younger were 2.31 times more likely to have CD if they lived in an area with NO₂ concentrations in the upper three quintiles than if they lived in an area with lower levels. There was no association with high SO₂ or PM₁₀ levels, however.

The risk for CD in these individuals increased in a linear fashion between those living in the third and those living in the fifth quintile. This did not apply to older CD patients (aged 44-57 years), who were less likely to live in high NO₂ areas.

Similarly, UC patients aged 20 or 25 years or younger were 2.62 and 2.00 times more likely, respectively, to live in regions with higher levels of SO₂ (third to fifth quintile) than in areas with lower levels, but no association was seen with NO₂ or PM₁₀ levels.

"The mechanisms by which air pollution may influence the development of IBD are speculative," write the authors.

They suggest that the adverse health effects are, at least in part, due to inflammation, adding that if air pollution influences gastrointestinal innate immunity, "then pollutants may predispose to IBD through altering interactions between the epithelial barrier and the intestinal microbiome."

Kaplan et al conclude: "If these findings are confirmed, then this work provides novel insight into the complex pathogenesis of IBD.

"Future studies will be needed to elucidate the mechanistic relationship between air pollution and IBD."

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