Lower risk of IBD with rural residence

Last Updated: 2017-07-31

By Will Boggs MD

NEW YORK (Reuters Health) - People living in rural households, especially from an early age, have a lower risk of inflammatory bowel disease (IBD), according to results from four Canadian provinces.

"These findings indicate the importance of early life environmental exposures in the subsequent development of IBD," Dr. Eric I. Benchimol from Children's Hospital of Eastern Ontario and University of Ottawa, Ontario told Reuters Health by email. "This effect has been seen in the IBD literature when examining other environmental risk factors, particularly early-life antibiotic use and air pollution. These risk factors seem to have the strongest effect of increasing the risk of childhood-onset IBD and not adult-onset disease."

Urban residence has been associated with a higher incidence of both Crohn's disease and ulcerative colitis, and some have proposed increased urbanization as one factor underlying the rising incidence of IBD.

Dr. Benchimol and colleagues in the Canadian Gastro-Intestinal Epidemiology Consortium used validated health administrative data to evaluate the incidence of IBD based on rural or urban residence, the association of rural/urban residence with age at diagnosis, and whether prolonged continuous exposure to one environment or the other after birth influenced the risk of developing IBD later in life.

The overall incidence of IBD was 10% lower in the rural population (30.72 per 100,000 person-years) than in the urban population (33.16 per 100,000 person-years), according to the July 25 online report in The American Journal of Gastroenterology.

The protective effect of rural residence was strongest in those who developed IBD before age 10 and between the ages of 10 and 18 and was similar in Crohn's disease and ulcerative colitis.

There was no significant association between residence and IBD incidence among individuals in older age groups.

Rural residence at birth was associated with significantly lower risk of IBD development later in life, and this effect remained stable with longer duration of continuous rural residence.

"Varying the definition of rural/urban resulted in varying degrees of association and even resulted in a lack of association for some definitions," the researchers note. "However, most definitions demonstrated the protective effect of rural residence on pediatric IBD, particularly in children <10 years."

"If we fully understood the environmental risk factors that increase the risk of IBD, we should be able to intervene to alter these risk factors and prevent Crohn's and colitis in people who were at higher risk (such as first-degree relatives of IBD patients, or those with specific genes)," Dr. Benchimol said. "Our findings indicate that if we were to intervene, we would probably provide the greatest benefit to altering exposure to these risk factors early in life, rather than in adulthood."

"Our findings also have research implications," he said. "The current main hypothesis regarding the cause of IBD is that environmental risk factors change the intestinal microbiome in genetically at-risk individuals, causing an increased risk of later developing IBD. The microbiome is thought to be established very early in life (probably the first two to three years of life) and is difficult to change permanently beyond that point. Therefore, our study implies that we should focus our research efforts on understanding the changes in the microbiome of young children early in life, and at the time of diagnosis with IBD, to better develop treatments that might bring the microbiome back to a normal or healthy state."

SOURCE: http://go.nature.com/2ud9OtI

Am J Gastroenterol 2017.