Both atopic and autoimmune arthritis conditions were independently associated with functional dyspepsia (FD) and irritable bowel syndrome (IBS), an Australian population-based study found. Furthermore, while functional gastrointestinal disorders (FGIDs) are associated with increased anxiety, and more than half of IBS cases are secondary to psychological disorders, the associations between FD, IBS, and immune disorders were independent of psychological distress.

“This suggests that different peripheral pathways may be involved in the pathogenesis of certain FGIDs,” wrote Nicholas J. Talley, MD, PhD, of the University of Newcastle in Callaghan, New South Wales, and colleagues in the study online in Alimentary Pharmacology and Therapeutics.

Conducted during 2015, the study surveyed 3,542 people randomly selected from the Australian population who returned a mailed questionnaire sent to 8,217 recipients (43% response rate). The sample was 52.7% female and had a mean age of 57.9. Those reporting a diagnosis of ulcerative colitis (1.6%) or Crohn’s disease (0.6%) were omitted from the dataset.

A total of 13.4% of the sample (95% CI 12.3-14.6) fulfilled Rome criteria for IBS. Of these, 2.6% (95% CI 2.1-3.2) met the criteria for constipation-predominant IBS (IBS-C); 3.4% (95% CI 2.8-4.0) for diarrhea-predominant IBS (IBS-D); 7.0% (95% CI 6.1-7.9) for mixed IBS; and 0.3% (95% CI 0.2-0.6) had post-infectious IBS (PI-IBS).

Rome criteria for FD were met by 16.9% (95% CI 15.6-18.2) of the sample, with 13.3% (95% CI 12.2-14.4) meeting the criteria for the FD subtype of postprandial distress syndrome and an additional 8.2% (95% CI 7.3%-9.2%) for the subtype of epigastric pain syndrome.

The survey queried respondents about physician diagnoses of autoimmune diseases, including scleroderma, psoriasis, rheumatoid arthritis, and diabetes mellitus, as well as allergic conditions such as asthma and food, pollen, and/or animal allergies.The prevalence of allergic conditions in the sample was as follows:

• Asthma 16.0%

• Food allergy 6.3%

• Pollen allergy 7.5%

• Animal allergy 3.7%

And for autoimmune diseases, the prevalences were:

• Diabetes mellitus 10.4%

• Rheumatoid arthritis 6.5%

• Psoriasis 4.3%

• Scleroderma 0.3%

When assessed for psychological distress, the respondents with IBS scored significantly higher on the 10-item Kessler scale compared with those without IBS, for a mean score of 6.05 (standard deviation 5.12) versus 3.0 (SD 3.80, P<0.001).

Similarly, people with FD had significantly higher Kessler scores, showing a mean score of 5.46 (SD 5.13) versus 3.0 (SD 3.78, P<0.001).

Psychological distress is considered an important determinant of FGIDs and is also associated with allergic conditions such as asthma and food allergy, Talley and co-authors noted. A 2014 study by their group of more than 20,000 primary care patients found that FD/IBS and atopic conditions (asthma, eczema, allergic rhinitis/hay fever, conjunctivitis) share an overlapping connection that is partly, but not completely, explained by a common association with anxiety and depression.

The current survey found that asthma, psoriasis, and rheumatoid arthritis, as well as allergies to food, pollen, and animals were significant univariate predictors of both disorders. The researchers found that after they controlled for age, gender, and psychological distress, the predictive odds ratios (ORs) for IBS were as follows:

• Food allergy 1.66 (95% CI 1.15-2.40, P=0.007)
• Psoriasis 1.81 (95% CI 1.19-2.74, P=0.006)
• Rheumatoid arthritis 1.68 (95% CI 1.15-2.4, P=0.007)

The study confirmed earlier research by Talley’s group showing that IBS is common in people with rheumatoid arthritis. For FD, the ORs were as follows:

• Asthma 1.32 (95% CI1.04-1.68, P=0.025)
• Food allergy 1.78 (95% CI 1.28-2.49, P=0.001)

The authors concluded that the association of atopy with FD and IBS is unlikely to be explained by psychological distress, suggesting that other pathways should be explored.

Study limitations, the researchers said, included the reliance on respondent self-reporting of physician diagnoses of allergic and immune disorders. Moreover, the survey sample reported a higher prevalence of diabetes and rheumatoid arthritis than other national surveys in Australia did, which may have been related to the older mean age of the respondents.

In addition, a modest difference in the age of responders versus non-responders was a potential source of bias, and hence the results may have underestimated the rates of allergic and autoimmune conditions because of a lower response rate in younger adults. Furthermore, the investigators did not assess psychological distress according to Diagnostic and Statistical Manual of Mental Disorders criteria for anxiety or depression disorders, and neither did the team assess somatization, a potentially confounding factor. Also, since the study was cross-sectional, it did not assess timing and could not clarify whether IBS/FD or allergic and autoimmune conditions came first.