Inflammatory bowel diseases (IBD), like Crohn’s Disease and Ulcerative Colitis, appear to be linked to Vitamin D supply. The lower someone’s Vitamin D serum level is, the more severe these conditions tend to be. A summary from 2014 concludes that IBD improves when Vitamin D levels are kept above 75 nmol/l.
Scotland has a high level of children with IBD and there is discussion whether low Vitamin D in early development (pregnancy and early childhood) might predispose people to such auto-immune diseases. In addition, children and adolescents with IBD are advised to prevent bone problems developing, by consuming enough Vitamin D to reach a 25(OH)D blood level of 80 nmol/l.
Even Irritable Bowel Syndrome (IBS) appears to improve when a person is not Vitamin D deficient.