Ulcerative colitis (UC) is an inflammatory disease involving the colonic mucosa, with bleedings and ulcerations. Consequences are destroyed mucosal barrier and increased permeability. Several cytokines are described to mediate the progressive course of ulcerative colitis and it is considered nowadays an immunologic disease. Patients with UC have often low levels of vitamin D and elevated prevalence of osteoporosis.||In vitro studies demonstrate that vitamin D has an immunomodulating effect, and may have a direct healing action on colonic mucosa has been described in animal studies. One can therefore rise a hypothesis that vitamin D supplementation could be crucial in patients with UC. To our knowledge, it has not been performed randomized clinical trials to study these possible effects of vitamin D and it has not been studied the effects of vitamin D on the relapse frequency and immunological composition of colic mucosa in patient with moderate to severe ulcerative colitis.||Objectives for our study are as follows: To examine if high-dose vitamin D supplementation in patients with moderate to severe ulcerative colitis:||reduces relapse frequency and increase the duration of the Infliximab induced remission|mediates and changes the cytokines composition in the colic mucosa|decreases the excretion of calprotectin in feces and reduces the concentration of inflammation markers|augments bone mass