Inclusion Criteria:  Adult patients (18 years or older) with inflammatory bowel disease (ulcerative colitis or Crohn's disease) Low serum vitamin D (25(OH)D ≤ 25 ng/mL Not currently on high dose vitamin D supplementation No prior bowel resections No antibiotic use in past 3 months.  Exclusion Criteria:  Patients less than 18 years old No diagnosis of IBD Serum 25(OH)D > 25 ng/mL Patients already on vitamin D supplementation Prior history of bowel surgery (colectomy or small bowel resections) Recent antibiotic use in past 3 months Renal Dysfunction History of Hypercalcemia History of HIV History of IgA deficiency History of Common Variable Immunodeficiency (CVID) Active C. diff infection