Irritable bowel syndrome (IBS) and functional dyspepsia are two common conditions that seem to defy simple medical explanation. Since neither has a clear cause (such as a structural abnormality in the GI tract) or a reliable diagnostic test to identify it, they’re considered diagnoses of exclusion. That means a doctor may tell you that you have IBS or functional dyspepsia if your symptoms match and they can rule out other disorders with similar symptoms. 

Your provider might also mention that depression and anxiety are common among people who have these digestive disorders.

Now a new study shows that allergies, asthma, and autoimmune disorders like psoriasis and rheumatoid arthritis also tend to overlap with having IBS and functional dyspepsia. According to the study, published in the journal Alimentary Pharmacology & Therapeutics, people who have an allergic or autoimmune condition are significantly more likely to have one of these digestive issues — and that the increased risk is “independent of psychological distress.”  

According to the findings, about 20 percent of people with rheumatoid arthritis also have IBS, a chronic disorder characterized by frequent bouts of diarrhea and/or constipation, excess gas, and lower abdominal pain. A substantial number of RA patients have functional dyspepsia, which causes chronic pain, nausea, and bloating in the upper part of the gastrointestinal tract. 

To conduct the study, researchers surveyed more than 3,500 people in Australia. Participants with an autoimmune inflammatory bowel disease (Crohn’s disease or ulcerative colitis) were excluded.  

Although psychological issues are common in people with autoimmune disorders and may play some role in the onset of IBS or functional dyspepsia, the authors concluded that anxiety and depression alone did not explain the increased prevalence of IBS and functional dyspepsia in this group.

So what’s the connection? No one knows for sure, but the authors note that “there is a growing body of literature that suggests that IBS and [functional dyspepsia] are disorders of immune activation.”  

While IBS and functional dyspepsia are not considered autoimmune ailments, there is reason to believe that some sort of immune system dysfunction might be involved in their development. Other research, for instance, has found that IBS patients have more T cells (immune cells) and mast cells (which release histamine) in their intestines compared to people who don’t have IBS. 

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