The epidemiology of inflammatory bowel disease: exploring the impacts of environmental factors

Inflammatory bowel diseases (IBD), such as ulcerative colitis and Crohn's disease, are distinct chronic immune-mediated intestinal inflammatory disorders. The pathogenesis of IBD is complex and involves a combination of genetic and environmental factors, the gut microbiome, and the host immune system. Despite significant progress in identifying the genetic factors of IBD, the increasing IBD incidence in recent decades, along with findings from immigrant and twin studies, suggest the involvement of environmental factors on IBD susceptibility. In this review, we summarize various up-to-date environmental factors, including early-life influences; diet, food, and nutritional exposures; urbanization and air pollution; smoking; appendectomy; medications; psychological stress; sleep; and latitude and geography.