In some situations, such as vitamin B12 deficiency associated with Crohn's disease of the terminal ileum, the deficiency can be determined by measurement of B12 in the blood. Supplementation is easily given as an intramuscular injection once a month. There are no easy methods to determine the presence of bone disease and no widely accepted methods of treatment. Patients with IBD who are able to eat a normal diet and have not had intestinal surgery usually have limited, if any, nutritional deficiencies. Because nutrients, vitamins and minerals are absorbed at different sites of the gastrointestinal tract, and Crohn's disease and ulcerative colitis commonly affect different parts of the intestine, one may expect different deficiencies in different patients.
Vitamin D is important for normal calcium metabolism and for proper bone formation.
IBD patients absorb water-soluble vitamins much more easily than fat soluble vitamins. Pills may be absorbed less than the liquid preparations and so liquid multivitamins may be desirable. In patients with active disease, one should consider checking blood levels of these vitamins and supplementing with aqueous preparations of Vitamins A, E and 1,25 dihydroxy-vitamin D in doses that normalize plasma levels. For those with mild disease, it seems prudent to take at least a standard multivitamin on a daily basis unless remission is long-standing, small intestinal resection has not been performed, and no medications are being used. If extensive ileal disease exists or small bowel surgery has been performed, B12 deficiency may be present.