Young immigrants to Canada at higher risk for IBD

Last Updated: 2015-03-11

By Lisa Rapaport

(Reuters Health) - The younger people are when they immigrate to Canada, the higher their risk for developing inflammatory bowel disease (IBD), a study finds.

"We were surprised by how clearly earlier life immigration was related to the risk, and that the children of almost all immigrant groups assumed the same risks as Canadians if they were born here," lead author Dr. Eric Benchimol at the Institute for Clinical Evaluative Sciences and the Children's Hospital of Eastern Ontario, told Reuters Health by phone.

Dr. Benchimol and colleagues analyzed administrative data from the government health plan on all residents of Ontario from 1994 to 2009, comparing immigrants who arrived after 1985 to people born in Canada or who immigrated earlier.

Immigrant children had significantly lower incidence of IBD than nonimmigrants, 7.3 per 100,000 years of follow-up versus 23.9, the authors reported March 10 online in the American Journal of Gastroenterology.

But the younger they were when they arrived in Canada, the more likely they were to develop IBD. Each year of increased age at arrival in the country was associated with a 1.34% decreased risk of IBD.

When the researchers looked at children of immigrant mothers - i.e., children born in Ontario after 1991 whose mothers arrived after 1985 - they found a lower relative incidence of IBD in those whose mothers came from Asia, Eastern Europe, Central Asia, Latin America, and the Caribbean. The incidence of IBD was similar for children of nonimmigrants and children of immigrants from the Middle East, Africa, South Asia, Western Europe, and North America.

This is the first study to show the increased risk in children of immigrants in Canada, a country with some of the world's highest rates of IBD, Dr. Benchimol said.

While the causes of IBD are unknown, the increased risks for children who immigrate to Canada suggest that the causes may be environmental, Dr. Benchimol said. It could be related to hygiene practices or antibiotic use, both of which could potentially alter the gut microbiome.

"We are working hard to try to identify what are the environmental risk factors and how they interact with genes in order to change the microbiome," Dr. Benchimol said.

The healthy bugs in the gut develop from about three months of age until about three years, and many environmental and cultural factors could potentially disrupt the formation of the microbiome, Dr. Gilaad Kaplan, a gastroenterologist and researcher at the University of Calgary, told Reuters Health in a phone interview.

"One early life factor that makes a big difference is breastfeeding, which appears to reduce the risk of IBD down the line," said Dr. Kaplan, who wasn't involved in the study. "In the western world and in the industrialized economy we do a lot less breastfeeding than we did 100 year ago."

Many Canadians are Caucasians of European descent, and while the genetic link to IBD hasn't been established, it's possible that one exists, Dr. Kaplan said. It's also possible that there's something about the environment of a westernized society that fosters IBD.

"We are starting to see IBD emerge in places like China as they become more like our westernized countries," Dr. Kaplan said. "And in this study, we're seeing that people who come from countries where we don't see a lot of IBD and they come to Canada and the first generation offspring as they are exposed to the Canadian environment start to have risks that look like Canadian kids."

SOURCE: http://bit.ly/1D6QDnX

Am J Gastroenterol 2015.