Background: The Faroe Islands have the world's highest recorded incidence of inflammatory bowel disease (IBD) . The Faroe Islands form part of the Danish realm and many Faroese immigrate to Denmark, where the IBD incidence is considerably lower. We studied the IBD incidence in first-, second-, and third-generation immigrants from the Faroe Islands to Denmark to assess the extent to which the immigrants adopt the lower IBD incidence of their new home country.
Methods: Data on Faroese-born Danish residents and their children were retrieved from the Danish Central Population Register for 1980–2014. Incident IBD cases for immigrants and the Danish background population were identified from the Danish National Patient Register. Standardised Incidence Ratios (SIRs) were used to compare the IBD risk in immigrants with that of Danish residents. 95% confidence intervals (CI) were calculated using the square-root transform.
Results: First-generation Faroese immigrants had a higher IBD incidence than Danes, SIR 1.25 (95% CI, 0.97;1.59) for men and 1.28 (95% CI, 1.05;1.53) for women. This excess risk derived from ulcerative colitis (UC), SIR 1.44 (95% CI, 1.10;1.87) for men and 1.36 (95% CI, 1.09;1.68) for women. No excess risk was found for Crohn's disease (CD). The excess UC risk disappeared over one generation in men and over two generations in women.
Conclusions: Although some impact of genetic dilution cannot be excluded, our findings indicate the importance of the gene-environment interplay in the development of UC, as the excess risk of UC in Faroese immigrants to Denmark disappeared over one to two generations.
 Burisch J, Pedersen N, Čuković-Čavka S, et al. (2014), East-West gradient in the incidence of inflammatory bowel disease in Europe: the ECCO-EpiCom inception cohort. Gut 2014 Apr;63(4):588–97.