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There is some evidence that environmental factors cause ulcerative colitis. The incidence of ulcerative colitis has increased dramatically between World War II and the 1980s.1 More recent data show that, in several areas, ulcerative colitis incidence decreases.2 3 Such large fluctuations are not consistent with a purely genetic disease, although the increased incidence could be attributed to a better recognition of the disease (coinciding with progress in endoscopy) and the recent decline, to a diagnostic transfer from ulcerative colitis to Crohn’s disease. Migrant studies have shown that ulcerative colitis incidence is at least as high in subjects originating from South Asia living in UK than in native British subjects,4 and has increased recently,5 thus suggesting that the British way of life increases the incidence of ulcerative colitis in migrants from Asia. Another evidence for the role of environment in ulcerative colitis comes from twin studies: disease concordance in monozygotic twins is only 19% in ulcerative colitis, as opposed to 50% in Crohn’s disease.6
What are the candidate environmental factors?
Ulcerative colitis is more frequent in non-smokers or ex-smokers than in current smokers, and in patients who have no history of appendectomy for appendicitis. Other environmental factors are likely to contribute to ulcerative colitis pathogenesis. For unexplained reasons, the variability of geographic distribution is lower for ulcerative colitis than for Crohn’s disease.7 However, geographic distributions of …
Competing interests None.
Provenance and peer review Commissioned; not externally peer reviewed.