Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Vitamin B12 exists in several forms and contains the mineral cobalt [ 1-4 ], so compounds with vitamin B12 activity are collectively called "cobalamins". Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism [ 5 ].
Vitamin B 12 , also called cobalamin , is a water-soluble vitamin that is involved in the metabolism of every cell of the human body: it is a cofactor in DNA synthesis , and in both fatty acid and amino acid metabolism .  It is particularly important in the normal functioning of the nervous system via its role in the synthesis of myelin ,   and in the maturation of developing red blood cells in the bone marrow .