Vitamin B12

Dr Daniel J Bell and Dr Craig Hacking et al.

Vitamin B12 (hydroxocobalamin, hydroxycobalamin or B12a) is a water-soluble vitamin, part of the vitamin B complex, and synthesized by intestinal flora that forms a cobalt-based coenzyme that is required for two vital cellular reactions, namely the production of methionine (an amino acid) and the metabolism of odd-number carbon atom fatty acids.

Related pathology

Vitamin B12 deficiency (hypocobalaminemia) leads to cell membrane dysfunction as it is incorporated with abnormal fatty acids, to which the central nervous system is particularly susceptible.

The commonest cause of deficiency of vitamin B12 is pernicious anemia, an autoimmune condition in which autoantibodies form against intrinsic factor (IF). IF is secreted in the stomach and binds to cobalamin. The IF-cobalamin complex is subsequently absorbed in the distal ileum. Lack of IF leads to malabsorption of vitamin B12. Chronic pathology of the terminal ileum (e.g. Crohn disease) and distal ileum surgical resection can also lead to reduced absorption of the complex and, therefore, hypocobalaminemia.

Due to its involvement with folate in the synthesis of amino acids and nucleic bases, B12 deficiency can precipitate folate deficiency.

See also

Share article

Article information

rID: 50111
Section: Pathology
Synonyms or Alternate Spellings:
  • Cobalamin (Cbl)
  • Cobalamin
  • Hydroxocobalamin
  • Vitamin B12a
  • Hydroxycobalamin

Support Radiopaedia and see fewer ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.