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



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.



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.



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.



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.
Department of Public Health, University of Copenhagen, Copenhagen, Denmark.|Department of Occupational Medicine and Public Health, The Faroese Hospital System, Tórshavn, Faroe Islands.
T
0000-0002-5242-955X
T
Hammer
Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
S N
SN
Lophaven
Medical Centre, National Hospital, Tórshavn, Faroe Islands.|Genetic Biobank, Tórshavn, Faroe Islands.
K R
KR
Nielsen
Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
M
M
von Euler-Chelpin
Department of Occupational Medicine and Public Health, The Faroese Hospital System, Tórshavn, Faroe Islands.
P
P
Weihe
Department of Gastroenterology, North Zealand Hospital, Copenhagen, Denmark.
P
P
Munkholm
Department of Gastroenterology, North Zealand Hospital, Copenhagen, Denmark.
J
0000-0002-3312-5139
J
Burisch
Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
E
E
Lynge
D000293:Adolescent; D000328:Adult; D032721:Adult Children / Q000706:statistics & numerical data; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003093:Colitis, Ulcerative / Q000453:epidemiology; D003424:Crohn Disease / Q000453:epidemiology; D003718:Denmark / Q000453:epidemiology; D004198:Disease Susceptibility; D054242:Emigrants and Immigrants / Q000706:statistics & numerical data*; D004777:Environment; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D015212:Inflammatory Bowel Diseases / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D012042:Registries; D012307:Risk Factors; D055815:Young Adult