Ambient air pollution and inflammatory bowel disease—a narrative review

Background and Objective: Environmental factors interact with host cells, primarily during specific vulnerable periods in a genetically predisposed individual. These factors can act as triggers of an exaggerated immune response contributing to the development of inflammatory bowel disease (IBD). The connection between host genome, gut microbiome, and environmental exposures in the development of IBD requires further clarification. The objective of this review is to explore air pollution as a possible risk factor for the development of IBD. Methods: We searched PubMed, Embase, and Cochrane Library databases to identify studies published up to September 15, 2023. We also analyzed references from relevant original articles and literature reviews to identify additional studies that were not encompassed in the initial database searches. For all eligible studies, we provided a narrative analysis of the findings. Key Content and Findings: The onset of IBD results from the association of various risk factors including genetic susceptibility, diet, immune dysregulation, and environmental factors that could potentially trigger the disease. Although there are conflicting results regarding the impact of air pollution on IBD pathogenesis, it appears that its role in increasing the expression of pro-inflammatory cytokines, disturbances in microbiota composition and colonic function is associated with a higher risk of incident ulcerative colitis (UC). Conclusions: Besides conflicting and inconsistent results from previous studies and notable knowledge gaps, there is a plausible chance that the development of IBD can be affected by air pollution. Future prospective studies are required to gain comprehensive insight into this correlation.