The role of vitamin D and ultraviolet radiation in inflammatory bowel disease

Vitamin D deficiency is associated with active Crohn's disease (CD) and ulcerative colitis, but it is not known if this is causal. We observed that vitamin D levels did not predict disease flares in CD and treatment of active CD led to a spontaneous rise in vitamin D levels. In murine colitis, vitamin D dropped significantly and mice on high vitamin D-containing diets demonstrated distinct faecal microbiome changes and also developed worse colitis. Taken together, these data suggest that vitamin D deficiency is a result rather than cause of intestinal inflammation and vitamin D supplementation is not protective.