Asthma increases the risk for Crohn’s disease and early- and late-onset ulcerative colitis, a Canadian population-based study suggests.

The study, “Asthma Is Associated With Subsequent Development of Inflammatory Bowel Disease: A Population-based Case–Control Study,” was published in the journal Clinical Gastroenterology and Hepatology.

Inflammatory diseases affecting the respiratory and gastrointestinal tracts, such as asthma and inflammatory bowel diseases (IBD), are the result of complex interactions between genetic and environmental factors. Several of these risk factors are common to both diseases. Some studies suggest a link between IBD and respiratory disorders, including asthma and chronic obstructive pulmonary disease.

However, asthma is often diagnosed earlier in life than IBD, which led the study’s authors to hypothesize that “individuals diagnosed with asthma were more likely to be subsequently diagnosed with IBD compared with those without asthma.” They performed a population-based, case-control study to determine the effect of asthma on the development of Crohn’s disease and ulcerative colitis, two forms of IBD.

Patient data were obtained from health administrative databases in the province of Alberta, Canada, including demographics, geographic information, and all hospitalizations. Authors identified 3,087 individuals with Crohn’s disease and 2,377 with ulcerative colitis. The analysis also included a large number of control participants — 402,800 — who were not diagnosed with IBD.

The results showed that “14.5% and 12.8% of individuals with Crohn’s disease and ulcerative colitis, respectively, had a diagnosis of asthma before the diagnosis of IBD. In contrast, 9.8% of control subjects were diagnosed with asthma before their randomly selected index date,” authors wrote.

This means that the risk for developing Crohn’s disease is significantly increased in those with pre-existing asthma. Patients’ ages at diagnosis did not modify the association between asthma and Crohn’s disease. For ulcerative colitis, however, asthma increased the risk only in patients diagnosed with ulcerative colitis before the age of 17 or after 40.

“Future studies are necessary to determine the mechanisms through which asthma and IBD are related,” the study concluded.