Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease. Evidence suggests that the concentration of serum VD is decreased in IBS patients, particularly in IBS-D. After giving a supplementation of VD, some symptoms of these patients were relieved to a certain degree. However, the specific mechanism still remains unclear.

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease, which is due to the gut microbiota disturbances, intestinal mucosal barrier dysfunction, and brain-gut axis dysfunction. Vitamin D (VD), a fat-soluble vitamin, has been found to be associated with gut microbiota, intestinal mucosal barrier and NLRP3 in inflammatory bowel disease, nonalcoholic fatty liver disease and other diseases. The concentration of serum VD is decreased in IBS patients, particularly in IBS-D. And the symptoms of IBS patients seems to be connected with the level of serum VD. After giving a supplementation of VD, some symptoms of these patients were relieved to a certain degree. However, the specific mechanism still remains unclear.We designed a study to figure out the effects of serum VD on gut microbiota, intestinal mucosal barrier and in patients with IBS-D.

Inclusion Criteria:

• ①IBS-D patients meeting the Roman IV diagnostic criteria: recurrent abdominal pain, averaging at least 1 day per week in the last 3 months, with 2 or more of the following: associated with defecation, accompanied by changes in defecation frequency, accompanied by changes in fecal properties or appearance. (Symptoms have been present for at least 6 months before diagnosis, and meet the above diagnostic criteria in the last 3 months; >1/4 (25%) stools were Bristol Stool Scale type 6 or 7, and <1/4 (25%) stools were Bristol Stool Scale type 1 or 2); ② The age ranged from 18 to 65.

Exclusion Criteria:

• ① History of other gastrointestinal diseases, such as inflammatory bowel disease, infection, cancer, abdominal radiation or surgery, hepatobiliary and pancreatic diseases; ② Taking vitamin D drugs, calcium, contraceptives, glucocorticoids, probiotics, antibiotics, antidepressants, etc.; ③ Pregnancy and lactation; ④ Diabetes mellitus, thyroid disease, osteoporosis, etc.; ⑤ Complicated with serious heart, liver, lung, kidney, blood, serious mental diseases and other systemic diseases; (6) Boston Intestinal Preparation Scale score <6; The cecum was not detected by endoscopy. ⑦ Unwilling to participate or unable to give informed consent.

IBS-D Patients who meet the above criteria