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Study finds high dose vitamin D supplementation significantly improves irritable bowel syndrome

Posted on: May 24, 2016   by  Amber Tovey

A randomized controlled trial discovered that 50,000 IU of vitamin D3 taken bimonthly for six months improved IBS symptoms.

Irritable bowel syndrome (IBS) is a chronic condition characterized by abdominal discomfort, altered bowel habits, diarrhea and constipation. Approximately one third of patients find the current treatments unsuccessful, leaving many patients to seek alternative medicine in an attempt to manage their symptoms.

Due to the role of vitamin D in the immune system and inflammation, researchers have begun studying the relationship between vitamin D and IBS; though, the research is still in its infancy. A case study reported that IBS symptoms significantly improved in a patient taking 3000 IU daily. Furthermore, an analysis of blogs and forums indicated that 37 IBS patients found improvements in their symptoms when supplementing with vitamin D. These findings led researchers to conduct a randomized controlled trial, the gold standard of research, to evaluate the effects of vitamin D supplementation on IBS symptoms.

A total of 74 men and women between the ages of 18 and 70 years were recruited from the outpatient clinic at Jundishapur University of Medical Sciences, Ahvaz, Iran. The patients were randomly selected to receive either 50,000 IU of vitamin D3 or placebo every two weeks for a period of six months. They reported their IBS symptoms at baseline and monthly during the intervention period.

The IBS severity was assessed with the IBS severity score system (IBSSS). The IBSS evaluates five common clinical symptoms associated with IBS: 1) severity of abdominal pain, 2) frequency of abdominal pain, 3) severity of abdominal distention or tightness, 4) dissatisfaction with bowel habits and 5) interference of life from IBS in general. Each item was scored on a scale from 0 to 100 with a low score indicating a mild form and a high score indicating a severe case. A 50 or more point reduction was regarded as a clinically significant improvement. Visual analog scale was used to evaluate pain and discomfort, with a high score indicating worse symptoms. Quality of life (QoL) was measured using a self-report QoL measure specific to IBS.

After the six month intervention, here is what the researchers found:

  • Vitamin D levels significantly increased from baseline in the vitamin D group (p
  • The placebo group’s vitamin D levels after the intervention period remained very similar to their baseline levels with an average of 18.62 ng/ml initially and an average of 20.91 ng/ml after the intervention (p > 0.05).
  • The IBSSS score was significantly improved in both the placebo group and the vitamin D group. Though, the average change in the IBSSS score in the vitamin D group was significantly greater than the placebo group with an average reduction of 53.8 points versus 16.8 points, respectively (p
  • All of the IBS symptoms significantly improved after six months in both groups. In the vitamin D group, all symptoms except dissatisfaction with bowel habits showed a significantly higher improvement than those in the placebo group (p
  • IBS-QoL also significantly improved in both groups. Again, a significantly greater improvement was seen in the vitamin D group compared to the placebo (p
  • The Vitamin D group experienced significant improvements in the mean IBS QoL scores in dysphoria, health worries, food avoidance, social reaction, relationships and sex life in comparison to the placebo group (P

The researchers concluded,

“The findings indicated that vitamin D supplement therapy has beneficial effects on IBS-QoL and the IBS severity score correlating with improved abdominal pain and distention, flatulence, rumbling, and overall GI symptoms as compared to the placebo group.”

The study yielded very strong results, suggesting that patients with IBS should add vitamin D supplementation to their treatment regimen. The study had the ability to produce such strong results through its randomized controlled trial design, which allowed the researchers to prove causation. In addition, the majority of patients included in the study were considered vitamin D insufficient or deficient at baseline. By the end of the trial, the majority of patients in the vitamin D group achieved sufficiency; whereas, the patients in the placebo group remained deficient.

While the study was relatively strong, there are still a few minor limitations to consider. Vitamin D supplementation was administered once every two weeks rather than on a daily basis. Lastly, the sample size was rather small.

Larger randomized controlled trials using a daily supplementation regimen are needed to evaluate the benefits of vitamin D supplementation on IBS symptoms.


Tovey, A. & Cannell, JJ. Study finds high dose vitamin D supplementation significantly improves irritable bowel syndrome. The Vitamin D Council Blog & Newsletter, 2016.


Abbasnezhad A, Amani R, Hajiani E & et al. Effect of vitamin D on gastrointestinal symptoms and health-related quality of life in irritable bowel syndrome patients: a randomized double-blind clinical. Neurogastroenterology & Motility, 2016.

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