Association between long-term ambient air pollution and incident inflammatory bowel disease across levels of adherence to a plant-based diet: a prospective cohort study in the UK Biobank.

Background: Ambient air pollution is a potential environmental risk factor for inflammatory bowel disease (IBD), whereas a plant-based diet may be protective. However, whether such a dietary pattern modifies the association between long-term air pollution exposure and IBD risk remains unclear. Methods: This prospective cohort study included 165,722 participants from the UK Biobank. Annual average concentrations of ambient air pollutants were estimated using air dispersion models. The plant-based diet index (PDI) was calculated based on the intake of 17 major food groups recorded in the 24-h dietary recall. Time-dependent Cox regression was applied to examine the association between long-term air pollution exposure and IBD risk, and stratified analyses along with interaction terms were performed to evaluate potential modification by the PDI. Results: This study demonstrated a positive association between air pollution exposure and the incidence of IBD, regardless of pollutant type. Air pollution exposure was positively associated with IBD risk among participants with lower PDI, whereas the point estimates were smaller and no longer statistically significant among those with higher PDI. A similar pattern was observed for ulcerative colitis. Conclusion: Long-term exposure to ambient air pollution may be associated with an increased risk of IBD. In the higher plant-based diet group, air pollution-related IBD risk was relatively lower, providing additional epidemiological evidence into the prevention and management of IBD.