This study aims to evaluate the effect of vitamin D3 supplementation on disease activity and quality of life in IBD patients deficient in vitamin D, and also help determine the optimal dose of vitamin D3 for them.

Hypothesis: Supplementation of vitamin D3 in IBD patients with hypovitaminosis D can improve their quality of life and decrease IBD activity.

The incidence of hypovitaminosis D has been reported to be as high as 75% in patients with IBD. However, it is unclear whether low vitamin D levels contribute to the pathogenesis of IBD or are a consequence of IBD. Recent animal data studies suggest that maintenance of the epithelial barrier integrity in the large intestine by vitamin D is important in preventing IBD.

However, more evidence is required to determine the effect of vitamin D3 supplementation in patients with IBD. Furthermore, there is no clear consensus regarding the appropriate dose of vitamin D supplementation in IBD patients.

Inclusion Criteria:

• Patients with inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• 18 years of age or older
• 25(OH)D levels <30ng/ml
• willing to give informed written consent

Exclusion Criteria:

• Age < 18 years
• Women who are pregnant or planning to become pregnant
• Patients already taking vitamin D3 ≥2,000 IU/daily prior to study enrollment