**3.5 Vitamin D and inflammatory bowel disease**

Vitamin D deficiency has been observed in patients with inflammatory bowel disease, Crohn's disease, and ulcerative colitis [126]. It was found to be related to disease activity in Crohn's disease and ulcerative colitis. Vitamin D supports the integrity of the intestinal barrier and is related to microbiota homeostasis in this cohort of patients [127, 128]. Thus, vitamin D may contribute to the prevention of inflammatory bowel disease by supporting the integrity of the intestinal barrier, contributing to bacterial homeostasis and ameliorating disease progression via anti-inflammatory action. Vitamin D deficiency in inflammatory bowel disease is aggravated by decreased absorption of the vitamin via the gastrointestinal tract [128].
