The purpose of this study is to test blood and tissue samples of people with Ulcerative Colitis (UC) to see what effects Vitamin D3 may have on the immune system. This research is being done because it could lead to the development of new treatment for people with Inflammatory Bowel Disease (IBD).

The primary endpoint of the trial is the change in colonic permeability as a global assessment of vitamin D3 effects throughout the colon in patients with Ulcerative Colitis. Secondary endpoints will be changes in colonic tight junction protein expression, and their relationship to serum vitamin D level, VDR expression, inflammatory cytokines, and histologic inflammation

Inclusion Criteria:

• Patients must be over 18 years of age
• have a diagnosis of UC as confirmed by histology.
• UC patients must have active but mild disease as confirmed by a Mayo Clinic endoscopy score from 2-4,
• not requiring medication adjustment during the trial.
• Patients must be capable of understanding the purpose, risks and expectations of study participation and willing to provide written informed consent.

Exclusion Criteria:

• Individuals on vitamin D or laxative therapy (except for purposes of endoscopy preparation),
• UC patients with fulminant colitis or active C difficile or other colonic infections,
• age<18 year old,
• individuals with bleeding disorders will be excluded from the study.