Background and Objectives: Irritable bowel syndrome (IBS) is a chronic disease with gastrointestinal disorders with serious effects on the quality of life. Recent investigations enumerated IBS among the complications of vitamin D deficiency. We investigated the effect of supplementation of vitamin D on improving the symptoms of IBS.

Materials and Methods: Sixty six patients who referred to the gastroenterology clinics and were diagnosed with IBS were invited to participate in this study. At the beginning of the study, the blood tests were done for all of them after fasting for about 12 to 14 hours. If the 25(OH)D serum level was lower than 30 ng/mL, these patients with IBS were eligible to enter to the study. At the beginning of the study, they were asked to prepare a 3-day (a holiday and two working days) note of their 24-hour food intakes. Then the clinical symptoms and quality of life questionnaire were filled out for them. Using the Stratified Blocked Randomization method, each person was devoted to receive either the vitamin D3 supplement or placebo. The intervention period in this research was 8 weeks. The patients in the test group took one 50000 IU dose of vitamin D3 weekly (as a pill), and people in the control group received a placebo (containing rice flour) weekly. Both groups received the same dietary recommendations.

Results: According to our results, vitamin D supplementation in patients with IBS may lead to a significant increase in 25(OH)D serum level (with a mean difference of less at the end of the study: -23/24 ±14), and  significant reduction  in the severity of clinical  symptoms (p-value<0.05).

Conclusion: It seems that taking a dose of vitamin D used in this study (50000 IU weekly) may be effective in improving IBS symptoms.

Keywords: Irritable bowel syndrome symptoms, Vitamin  D3, Clinical trial