Inflammatory bowel diseases in Faroese‐born Danish residents and their offspring: further evidence of the dominant role of environmental factors in IBD development

BackgroundThe incidence of inflammatory bowel disease (IBD) is record high in theFaroe Islands, and many Faroese emigrate to Denmark, where the IBD inci-dence is considerably lower.AimTo study the IBD incidence in first-, second- and third-generation immi-grants from the Faroe Islands to Denmark to assess the extent to which theimmigrants adopt the lower IBD incidence of their new home country.MethodsData on Faroese-born Danish residents and their children were retrievedfrom the Danish Central Population Register for 1980–2014. Incident IBDcases were identified from the Danish National Patient Register. Standard-ised Incidence Ratios (SIRs) were used to compare the IBD risk in immi-grants with that of Danes. 95% confidence intervals (CI) were calculatedusing the square-root transform.ResultsFirst-generation Faroese immigrants had a higher IBD incidence thanDanes, 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. Noexcess risk was found for Crohn’s disease (CD). The UC risk was nearlydoubled during the immigrants’ first 10 years in Denmark; SIR 2.13 (95%CI, 1.52–2.92) for men and 1.63 (95% CI, 1.19–2.18) for women.ConclusionsAlthough some impact of genetic dilution cannot be excluded, our findingsindicate importance of gene-environment interplay in UC, as the excess UCrisk in Faroese immigrants to Denmark disappeared over time and overone generation in men and over two generations in women.