Patients with UC will be recruited and consented prior to colonoscopy or flexible sigmoidoscopy. All patients will be age 18 or older with a known history of UC that has been confirmed by biopsy and an extent of disease of at least 20cm proximal to the anus. Clinical data will be collected on the patient's age, disease duration, family history of IBD, smoking status and history, as well as current medications for IBD through a questionnaire. Data will also be collected regarding current vitamin D supplementation (if taking) and dose. Prior to the endoscopic procedure, peripheral blood will be drawn into two 10ml red top tubes. At the time of endoscopy, five standard size mucosal pinch biopsies will be obtained from 20cm proximal to the anus. . A bar-coded unique identifier label will be applied to each sample. One biopsy will be placed in formalin. Paraffin samples will be maintained at room temperature. Following to the endoscopic procedure, the patient's physician will complete a Mayo score based on the patients current symptoms and endoscopic disease severity. Comparison will be made between disease activity, serum serum 25 hydroxyvitamin D level, and mucosal expression of tight junction proteins as well as proinflammatory cytokines.