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Immigrant study shows impact of environmental factors in IBD
Danish residents who immigrated from the Faroe Islands had about a 25% higher incidence of IBD and a 44% higher incidence of ulcerative colitis than native Danes, but third-generation immigrants had the same risk for UC as the general population, according to recent study data.
These findings highlight the impact of environmental factors in the development of IBD, researchers concluded.
“The Faroe Islands have the highest incidence of IBD in Europe at 84 per 100,000,” Turid Hammer, MSc, a research assistant in the department of public health at the University of Copenhagen, and the department of occupational medicine and public health in the Faroese Hospital System, told Healio Gastroenterology. “We investigated the incidence of IBD in first-, second- and third-generation immigrants from the Faroe Islands to Denmark, as many move to Denmark, where the incidence of IBD is considerably lower.”
Turid Hammer
Hammer and colleagues obtained data on 57,373 Faroese-born Danish residents and their children from 1980-2014 using the Danish Central Population Register, identified incident IBD cases using the Danish National Patient Register, and compared IBD risk between immigrants and Danes.
“First-generation Faroese immigrants had a higher incidence of IBD than Danes and the excess risk derived from ulcerative colitis,” Hammer said. “No excess risk was found for Crohn’s disease.”
The standardized incidence ratios for IBD among first-generation immigrants were 1.25 (95% CI, 0.97-1.59) in men and 1.28 (95% CI, 1.05-1.53) in women, and for UC they were 1.44 (95% CI, 1.1-1.87) and 1.36 (95% CI, 1.09-1.68), respectively.
The excess UC risk was nearly twice as high during the first 10 years after they immigrated (SIR = 2.13; 95% CI, 1.52-2.92 for men and SIR = 1.63; 95% CI, 1.19-2.18 for women), but after 10 years the UC risk became comparable to that of Danes.
Among second-generation immigrants, the SIRs for UC were 1.01 (95% CI, 0.71-1.4) in males and 1.29 (95% CI, 0.97-1.69) in females, and among third-generation immigrants they were 0.87 (95% CI, 0.39-1.66) and 1.18 (95% CI, 0.62-2.02), respectively.
“The excess UC risk disappeared over one generation in men and over two generations in women, stressing the importance of the gene–environment interplay in the development of UC,” Hammer said.
Notably, third-generation female, but not male, immigrants had an excess risk for Crohn’s disease compared with Danes (SIR = 1.83; 95% CI, 1.08-2.9), which the investigators characterized as surprising.
The researchers believe this is the first nationwide study of IBD incidence among immigrants from a high-risk to a lower-risk country, and noted that studies evaluating a reversed situation — for example, a Canadian study of immigrants from a low-risk to a high-risk country that found an increased IBD risk in the second-generation — strengthen the evidence that environmental exposures, which remain to be identified, play a significant role in the etiology of ulcerative colitis. – by Adam Leitenberger
Disclosures: One of the researchers’ reports he served as a speaker for AbbVie, Takeda and MSD, and served as an advisory board member for AbbVie, Celgene and Janssen.