The inflammatory bowel diseases and ambient air pollution: A novel association

Objectives: The inflammatory bowel diseases (IBDs) emerged after industrialization. We studied whether ambient air pollution levels were associated with the incidence of IBD. Methods: The health improvement network (THIN) database in the United Kingdom was used to identify incident cases of Crohn's disease (n367) or ulcerative colitis (n591), and age- and sex-matched controls. Conditional logistic regression analyses assessed whether IBD patients were more likely to live in areas of higher ambient concentrations of nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and particulate matter <10μm (PM₁₀), as determined by using quintiles of concentrations, after adjusting for smoking, socioeconomic status, non-steroidal anti-inflammatory drugs (NSAIDs), and appendectomy. Stratified analyses investigated effects by age. Results: Overall, NO₂, SO₂, and PM₁₀ were not associated with the risk of IBD. However, individuals 23 years were more likely to be diagnosed with Crohn's disease if they lived in regions with NO₂ concentrations within the upper three quintiles (odds ratio (OR)2.31; 95% confidence interval (CI)1.25-4.28), after adjusting for confounders. Among these Crohn's disease patients, the adjusted OR increased linearly across quintile levels for NO₂ (P=0.02). Crohn's disease patients aged 44-57 years were less likely to live in regions of higher NO₂ (OR=0.56; 95% CI0.33-0.95) and PM₁₀ (OR=0.48; 95% CI0.29-0.80). Ulcerative colitis patients 25 years (OR=2.00; 95% CI1.08-3.72) were more likely to live in regions of higher SO₂; however, a dose-response effect was not observed. Conclusions: On the whole, air pollution exposure was not associated with the incidence of IBD. However, residential exposures to SO₂ and NO₂ may increase the risk of early-onset ulcerative colitis and Crohn's disease, respectively. Future studies are needed to explore the age-specific effects of air pollution exposure on IBD risk.