Inflammatory bowel disease rate higher among urban residents

Children born in urban areas are more likely to develop inflammatory bowel disease (IBD) when they grow up than are children born in rural areas, a Canadian study showed.

With rising rates of IBD in developing nations and urbanized areas, the investigators interpreted these findings as a positive step toward further understanding, and eventually eliminating, the risk of developing IBD.

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The retrospective, population-based study gathered a total of 45,567 IBD patients: 6,662 living in rural residences and 38,905 living in urban residences in Nova Scotia, Ontario, Alberta, and Manitoba, Canada.

Patients in rural areas were on average older than urban patients (average age, 43 years vs. 40 years). Rural patients were also, on average, diagnosed later than were urban patients, with an average age at diagnosis of 42 years, compared with 38 years for urban residents.

The IBD incidence rate among urban patients was 33.16/100,000 (95% CI, 27.24-39.08), compared with 30.72/100,000 (95% CI, 23.81-37.64) among rural residents (Am J Gastroenterol. 2017 Jul 25. doi: 10.1038/ajg.2017.208).

Exposure to these environments while growing up was especially significant, with the lowest rate among children younger than 10 years in rural areas (incidence rate ratio, 0.58; 95% CI, 0.43-0.73), followed by adolescents between 10 and 17.9 years (IRR, 0.72; 95% CI, 0.64-0.81), according to investigators.

The incidence rate of IBD among rural children stayed consistent from birth through age 5 years, which may be evidence that development of IBD later in life is correlated with patients’ time in rural areas, the investigators reported.

Although Dr. Benchimol and his coauthors could not point to the exact reason for these results, they said factors such as diet and early exposure to animals, which may help develop useful bacteria that could help fight IBD development, are possible explanations.

“The mechanism by which rurality protects against IBD is uncertain, and may include dietary and lifestyle factors, environmental exposures, or segregation of individuals with different genetic risk profiles,” the investigators wrote. “These effects may be stronger in children because their gut microbiome is in evolution and may be vulnerable to changes in the first 2 years of life.”

This study was limited by certain classification factors, such as what constitutes an urban or rural area, which may have affected the outcomes. A lack of information on the effects of confounding factors, particularly ethnicity, genotype, phenotype, disease severity, or family history also limited this study, the investigators said.

The Janssen Future Leaders in IBD Program funded the study. Investigators reported receiving financial support from or holding leadership positions in the Canadian Institutes of Health Research, the Canadian Child Health Clinician Scientist program, and the Nova Scotia Health Research Foundation.

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