Here are some studies about vitamin D and inflammatory bowel disease:
Paediatric IBD Patients Do Not Meet the Daily Recommendations of Vitamin D and Calcium Intake: Survey Based Analysis in a Tertiary Centre (2017)
Conclusion: A survey of 151 pediatric inflammatory bowel disease patients found that 75% of the children had low vitamin D levels.
1,25-Dihydroxycholecalciferol Prevents and Ameliorates Symptoms of Experimental Murine Inflammatory Bowel Disease (2000)
Conclusion: In an experiment involving infant mice, engineered vitamin D deficiency was found to be deadly for the pups. Dissection revealed that one fatal vitamin D-deficiency symptom was severe inflammatory bowel disease, which induced diarrhea in the pups. The vitamin D-deficient pups were also growth retarded compared to vitamin D-sufficient mice.