||A group of chemical compounds that contain cobalt and are needed for certain chemical reactions in the body. Vitamin B12 is involved in maintaining healthy nerve cells and red blood cells. It is needed to make DNA (the genetic material in all cells), and is required for the metabolism (chemical changes that take place in the tissues to produce energy and the basic materials needed by the body) of carbohydrate, fat, and protein. Also called cobalamin. For more information see the NIH Office of Dietary Supplements Vitamin B12 fact sheet.