Environmental risk factors in Crohn's disease and ulcerative colitis: an update

Rapid increase in Crohn's disease (CD) and ulcerative colitis (UC) incidence in developed countries, occurrence of CD in spouses and lack of complete concordance in monozygotic twins are strong arguments for the role of environmental factors in inflammatory bowel disease (IBD). Only two environmental factors have an established role in IBD. Smoking is a risk factor for CD and a protective factor for UC; appendectomy is a protective factor for UC. Many other environmental factors for IBD have been investigated. These are infectious agents, diet, drugs, stress and socio-economic factors. They are detailed in this paper. Among them, adherent invasive E. coli, infectious gastroenteritis, oral contraceptives and antibiotics could play a role in CD. To date, three theories integrate environmental factors to pathogenesis of IBD: hygiene, infection and cold chain. Much work remains to be done to identify risk factors for IBD. As exemplified by smoking, research of environmental risk factors of IBD is useful since it may lead to an improved disease course among patients and perhaps, to appropriate prevention among predisposed subjects. Further studies in this field are eagerly awaited.