Cyanocobalamin, or vitamin B12, is a B-vitamin. It is found in a variety of foods such as fish, shellfish, meats, and dairy products. Deficiency in healthy individuals is rare; the elderly, strict vegetarians (i.e., vegan), and patients with malabsorption problems are more likely to become deficient. If vitamin B12 deficiency is not treated with a vitamin B12 supplement, then anemia, intestinal problems, and irreversible nerve damage may occur. Oral therapy is not always effective, as some persons lack in- trinsic factor, an endogenous substance produced by the stomach and necessary for oral B12 absorption. Other patients may not be able to absorb oral vitamin B12 due to surgical removal or dysfunction of the intestines in the area where absorption of vitamin B12 occurs.