vitamin B12

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Vitamin B12, or cyanocobalamin, is a group of cobalt-containing water-soluble vitamins. They are coenzymes necessary for red blood cell production - folate polyglutamate is the major red cell form of folate.

Vitamin B12 is derived primarily from food of animal origin, including dairy products.

Absorption of B12 from the gastrointestinal tract is dependent on acid and intrinsic factor secreted by the gastric mucosa.

The recommended daily average intake in the adult is 3-5 micrograms. A normal liver stores about 3 mg which is sufficient for several years.


  • in humans, only two enzymatic reactions are known to be dependent on vitamin B12
    • methylmalonic acid is converted to succinyl-CoA using vitamin B12 as a cofactor
      • vitamin B12 deficiency can lead to increased levels of serum methylmalonic acid
    • homocysteine is converted to methionine by using vitamin B12 and folic acid as cofactors
      • therefore a deficiency of vitamin B12 or folic acid may lead to increased homocysteine levels

Last reviewed 08/2021