Irritable Bowel Syndrome (IBS) impacts the quality of life; its incidence has been increasing over last two decades to become the commonest gastrointestinal disease is. Pharmacological agents going to target the underlying illness mechanisms have been developed with an increasing awareness of IBS pathophysiology. Possible mechanisms implicated in IBS pathogenesis can be modulated by vitamin D, Owing to its possible role as immune modulator, and anti-microbial and anti-inflammatory agent. The aim of this research was to evaluate the impact of food rich in vitamin D and supplementation on irritable bowel syndrome symptoms in undergraduate medical students with vitamin D deficiency, as part of Nutritional Assessment of Medical Students of Ain Shams University (NAMS/ASU). Subjects and Methods: This is a prospective cohort study done as a part of The Nutritional Assessment of Medical Students of Ain Shams University (NAMS/ASU), the project was designed to evaluate the nutritional status of 1225 medical student of the undergraduate medical students. This sector of the project included 40 vitamin D deficient (<20IU), IBS (according to ROME IV criteria) undergraduate medical students Those students were selected after: - History taking stressing on demographic data, IBS symptoms according to ROME IV criteria and chronic illness (DM, HTN, IBD,…..) -Vitamin D level by ELISA (Ain Shams University Central Labs) with deficiency diagnosed at (<20 IU), (50 nmol/liter) Those students were further subjected to: -Diet instruction for irritable bowel syndrome and lifestyle advice (eg. Regular eating pattern, Limiting the intake of triggering agents, ensuring a good hydration and regular physical activity, take the time to eat, sit down to eat, chew the food carefully) -An advice to increase intake of vitamin D rich food and Vitamin D Oral Drops Cholecalciferol 42000 IU / week. Enrolled students were reassessed after 12 weeks through: Re-evaluation of IBS symptoms using ROME IV criteria by the same investigator Vitamin D level by ELISA using the same kits at the same laboratory (Ain Shams University Central Labs). Informed written consent was obtained. Approval by the ethical committee was obtained. Data collection was done, tabulated and analyzed (SPSS Inc., Chicago, Illinois, USA). Probability (P-value) – The P-value of >0.05 was deemed insignificant. Results: Forty undergraduate medical students were involved in this sector of (NAMS/ASU) with mean age= 22.33±1.37, mean BMI=23.75±3.02, 65% of included students were females. The included students had mean vitamin D= 11.68±8.17 and 44.30±16.18 before and after 12 weeks of VIT D supplementation respectively, 97.5% of the participants achieved vitamin D normalization by the end of the study, After three months of vitamin D supplementation, 47.5% (19 students) of the study population did not fulfill ROME IV criteria any more (no IBS symptoms), while 52.5% (21 students) of them continued to have ROME IV criteria, yet with partial relief of symptoms with a significantly higher vitamin D levels in the students with complete resolution of symptoms at the end of the study duration (P value=0.013) Conclusion: Vitamin D supplementation plays a therapeutic role in the control of IBS in vitamin D deficient IBS patients.