Canadian researcher Dr. M. Ellen Kuenzig of the University of Calgary in Alberta, Canada has led a research team that found evidence that asthma is linked to inflammatory bowel disease. Dr. Kuenzig and her colleagues conducted a case-control study, which looks at health-related data within large populations of people. In the province of Alberta, they evaluated information collected from over 400 thousand patients. Of these, 5464 patients had inflammatory bowel disease.
Scientists have previously speculated an association between asthma and inflammatory bowel.
Why did Dr. Keunzig want to study diseases that seem so different from each other? It turns out that there’s been suspicion for a while that these seemingly different diseases are related. There are already published research studies suggesting associations between asthma and inflammatory bowel diseases. Some have found similar gene variants that are found in both asthma and inflammatory bowel patients. It’s also been shown that babies have higher rates of these diseases if they are not breastfed or had been exposed to antibiotics during infancy.
Scientists and doctors don’t know yet how asthma and inflammatory bowel disease develop. There are theories pointing to both genetic and environmental triggers, though no one has really pinpointed any answers yet. Though the exact mechanism for developing these diseases is unknown, we do know that there are similarities between the gut and the lungs.
There are similarities between the gut and lungs that could explain the link between asthma and inflammatory bowel disease.
The bowel and lung actually have more in common than most people think. Though they are so far apart in the body and seem to serve radically different functions, they both come from similar primitive structures. Both the lung and the gut tissues come from the foregut as a human embryo develops in the womb. Because of this, they share a similar inner lining called the epithelium. The epithelium is a specialized layer of organized cells that line the internal spaces of our body’s organs. Both lung and gut epithelium are similar in the fact that they both can produce mucous.
Because the lungs and bowel share similar internal epithelium, scientists have wondered whether this similarity might be linked to asthma and inflammatory bowel. Both asthma and inflammatory bowel have been shown in other studies to be related to problems with the integrity of the epithelial layers. This causes the protective layer to become dysfunctional as a barrier, which leads to problems with preventing invading microbes such as bacteria. It’s been theorized that due to this epithelial defect, the body’s ability to fight off microbes is derailed. Combined with improperly controlled inflammation, a person can end up with diseases like asthma or inflammatory bowel. This explanation might also explain why certain bacterial factors and environmental triggers play such a role in the progression of these diseases.
Dr. Kuenzig and her colleagues decided to study this association on a population-based level by looking at patient data.
The researchers wanted to gather more data and find out whether an association exists between asthma and inflammatory bowel disease. The research team went to health databases carrying a huge wealth of information about the large population of people living in Alberta, Canada. Using special algorithms and medical billing codes, they were able to identify 2377 cases of ulcerative colitis, 3087 cases of Crohn’s disease, and 402,800 control patients without either disease. From these patient study groups, they then used more algorithms to identify whether these patients had a pre-existing diagnosis of asthma.
The study results provide evidence supporting the previous scientific thoughts on asthma’s connection to inflammatory bowel disease.
From their data, Dr. Kuenzig and her team saw that 14.5% of people with Crohn’s and 12.8% of people with ulcerative colitis had been diagnosed with asthma prior to their inflammatory bowel disease. They concluded this was statistically meaningful compared to the 9.8% of patients diagnosed previously with asthma who did not have any Crohn's or ulcerative colitis.
When calculating an odds ratio, Dr. Kuenzig compared groups based on specific age groups. She and her colleagues found that people with asthma were 1.45 times more likely to have Crohn’s regardless of age. However, for ulcerative colitis, the trend was age-specific. For those under age 16, asthma increased odds of having ulcerative colitis by 1.49. People over 40 with asthma also increased odds of having ulcerative colitis by 1.57. For everyone between age 17-40, having a diagnosis of asthma did not increase the odds of being diagnosed with ulcerative colitis.
From the data they gathered, the scientists say that further study is needed to understand the connection between asthma and inflammatory bowel.
It appears that people who have asthma may have an increased risk of developing inflammatory bowel disease later in life. Dr. Kuenzig’s findings suggest that any asthmatic patients with bowel symptoms may benefit from a low-threshold for a referral to a gastroenterologist.
Moreover, Dr. Kuenzig points out that it was an important distinction in their study that there were age-related differences in the trends seen for ulcerative colitis. Because it’s unclear how the disease actually develops, a person’s age and even gender may greatly influence someone’s chances of having the disease. That’s why she advises any future research in this connection should pay attention to age and gender-specific differences.
The study had some limitations in design.
Though the study had strength in the ability to capture such a large number of patients, there were some study limitations that could significantly affect the validity of the results. For example, the way that they extracted information from databases limited their ability to accurately measure important confounding factors, such as smoking. This is definitely a problem because smoking is associated with both Crohn’s and ulcerative colitis.
Besides confounding factors that were unaccounted for, the case-control design made it difficult for anyone to make a statement as to how asthma is connected to inflammatory bowel diseases. We still don’t know much about what makes these two diseases related to each other. Though we have evidence for a relationship between the two very different conditions, we have no idea what the cause of this relationship really is.
The study concluded that asthma was associated with inflammatory bowel, and more research is needed to elicit the finer details about why.
From the results, researchers concluded that there was a trend between asthma and Crohn’s disease, as well as early and late-onset ulcerative colitis. We still don’t know why there is this trend between asthma and inflammatory bowel. It’s likely that they share similar means of pathogenesis, meaning that the causes for its development are likely the same. Whether it's genetic factors or triggers from the environment, there needs to be further research into the mechanism of both diseases.
Dr. Kuenzig’s team published their findings in the September issue of Clinical Gastroenterology and Hepatology. Here, you can read more about their research titled: “Asthma is Associated With Subsequent Development of Inflammatory Bowel Disease: A Population-Based Case-Control Study”.