Inflammatory bowel disease ((IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC)), is a chronic, immune-mediated disease characterized by recurrent episodes of relapse. The incidence of IBD is increasing worldwide and poses as a burden that reduces quality of life and has a significant impact on health care resources. The advent of monoclonal antibodies to tumor necrosis factor-α (anti-TNF) has revolutionized treatment of IBD, improving rates of remission and reducing hospitalizations and surgeries. Nevertheless, many patients do not adequately respond to these therapies or lose response over time. Thus, there is an important need for novel immunomodulating agents to improve our ability to achieve remission. Besides its traditional role in bone homeostasis, several studies have recognized the important role Vitamin D plays in modulating the immune response, cancer, and cardiovascular disease. Specifically, Vitamin D may mediate immunity by modulating autophagy in leukocytes and regulating the gut microbiome. Thus, Vitamin D may play an important role in IBD. Furthermore, evidence suggests that the effect of vitamin D may be mediated through the TNF-α pathway, suggesting a synergy with anti-TNF therapy. This is a randomized, double blind, placebo-controlled trial to study the effect of Vitamin D3 as an adjunct therapy for patients with active CD, UC, or IBD unspecified who are undergoing anti-TNF induction therapy.