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

BACKGROUND: The incidence of inflammatory bowel disease (IBD) is record high in the Faroe Islands, and many Faroese emigrate to Denmark, where the IBD incidence is considerably lower. AIM: To study 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 were identified from the Danish National Patient Register. Standardised Incidence Ratios (SIRs) were used to compare the IBD risk in immigrants with that of Danes. 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 UC risk was nearly doubled 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. CONCLUSIONS: Although some impact of genetic dilution cannot be excluded, our findings indicate importance of gene-environment interplay in UC, as the excess UC risk in Faroese immigrants to Denmark disappeared over time and over one generation in men and over two generations in women.

The incidence of inflammatory bowel disease in Denmark 1980-2013: a nationwide cohort study.

BACKGROUND: Globally, the incidence rates of inflammatory bowel disease (IBD) are increasing; however, data from high-incidence areas are conflicting. Previous studies in Denmark have assessed incidence rates of Crohn's disease (CD) and ulcerative colitis (UC) using short observation periods. AIM: To investigate trends in IBD incidence in Denmark over a thirty-year period using nationwide data. METHODS: Patients diagnosed with CD or UC in Denmark between 1980 and 2013 were identified in the Danish National Patient Registry (NPR) and included in a nationwide cohort. Incidence rates estimated using different numbers of National Patient Registry records (≥1, 2, 3 or 4) required for case definition were compared. RESULTS: From 1980 to 2013 the incidence of CD increased from 5.2 (95% CI: 5.0-5.4) per 100 000 to 9.1 (95% CI: 8.7-9.5) per 100 000 and the incidence of UC increased from 10.7 (95% CI: 10.4-11.0) per 100 000 to 18.6 (95% CI: 18.0-19.2) per 100 000. The increased incidence in CD and UC was independent of gender. The annual increase in incidence rate was greatest in patients aged <15 years for CD and those older than 15 years for UC. For both CD and UC the incidence rates for females were significantly higher than for males. The number of registry records chosen to define IBD cases greatly influenced incidence estimates. CONCLUSIONS: The incidence of IBD in Denmark continues to increase and is among the highest in the world. Using at ≥2 records of IBD diagnosis in the Danish National Patient Registry will result in more valid incidence estimates.