Study Not Enough to Justify Taking Excess Vitamin D for IBS

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Irritable bowel syndrome (IBS) is a chronic, disruptive, and overall displeasing situation to find yourself facing. Consequently, there is a lot of research going on about ways to better manage, prevent, or cure IBS using a variety of methods. One such study, a small double-blinded and randomized clinical trial from Iran, shows some interesting promise for using vitamin D as an IBS treatment. While the study made use of the gold standard for controls, this doesn’t mean its results—which showed distinct symptom improvement in the treatment group—should be taken at face value. Let’s poke them and see what happens, shall we?

The Vitamin D for IBS Study: Summary

  • The study had 90 participants that were randomized into treatment and control groups
  • The treatment group was given a megadose vitamin D supplement (50, 000 IU) every two weeks for six months
  • Clinical signs such as abdominal pain, bloating, abdominal distension, and issues with stool consistency were assessed at baseline and every two weeks during the study
  • Symptom severity scores were calculated at baseline and at the end of the six month period
  • An IBS-specific quality of life scoring questionnaire was used at baseline and at the end of the six month period
  • Vitamin D levels were calculated at baseline and after the six month period
  • Both groups showed improvements in symptom severity scores, quality of life, and clinical symptoms, though the vitamin D group had greater improvements in all areas except satisfaction with bowel habits
  • At the start of the study, 65% of the treatment group had low-to-deficient levels of vitamin D. At the end, 97% had above average-to-high levels

Various inflammation and blood serum markers were also measured at baseline and at the endpoint, but these findings are not mentioned in the abstract and the full study is behind a paywall. Parsing the results and seeing how seriously they should be taken will therefore call for some reading between the lines, a bit of understanding of measurement uses, and information gleaned from others who have a journal subscription.

Breaking Things Down

To get the most obvious out of the way: at only 90 participants this is an indisputably small clinical trial. As I’ve mentioned before, small sample sizes tend to produce exaggerated results that might diminish or vanish in larger samples and are more vulnerable to false positives in general. This doesn’t mean the study can be automatically tossed, but it’s something important to keep in mind when evaluating the findings and trying to draw broader knowledge.

Moving past the size issue, there is a noticeable oddity in the way the primary outcomes are measured. The clinical signs are measured every two weeks while the actual severity of symptoms is only measured at baseline and the end. This seems like a weird discrepancy since it means that the symptom severity results are inherently less reliable than the clinical sign results. A six month gap leaves more room for memory error than a two week one.

Lastly, the blood serum measurements are neither discussed, explained, or justified. The abstract mentions that vitamin D could ease IBS “though its beneficial effects on psychological factors and inflammation” (emphasis added) except this has one very distinct problem: irritable bowel syndrome has nothing to do with inflammation. Although the condition is sometimes confused with inflammatory bowel disease the two are quite different. How addressing inflammation could help IBS is not elaborated on.

Bottom Line

  • The participants all reported that they improved during the trial and the vitamin D group reported stronger levels of improvement, but the sample size is too small to tell how meaningful this distinction is or if it’s just a false positive
  • Inflammation measurements don’t make much sense when looking at a disorder unrelated to inflammation
  • Contrary to what the Vitamin D Council may pitch, this study is nowhere near enough to justify taking excess vitamin D—especially in megadose levels—for IBS


Abbasnezhad, A., “Effect of vitamin D on gastrointestinal symptoms and health-related quality of life in irritable bowel syndrome patients: a randomized double-blind clinical trial,” Neurogastroenterology and Motility, 2016; 10.1111/nmo.12851.
Tovey, A., “Study finds high dose vitamin D supplementation significantly improves irritable bowel syndrome,” Vitamin D Council web site, May 24, 2016;, last accessed May 25, 2016.