Medical Definition of Vitamin B12

Vitamin B12: A vitamin important for the normal formation of red blood cells and the health of the nerve tissues. Undetected and untreated vitamin B12 deficiency can lead to anemia and permanent nerve and brain damage.

Pernicious anemia is a blood disorder caused by inadequate vitamin B12 in the blood. Patients who have this disorder do not produce the protein substance in the stomach that allows the body to absorb vitamin B12. This substance is called intrinsic factor (IF).

Patients with Crohn's disease involving the small intestine (Crohn's ileitis) or who have undergone small intestine resection may not be able to absorb vitamin B12.

Strict vegetarians who consume no animal products can develop B12 deficiency since there is a lack of B12 in vegetables.

Also called cobalamin.

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Last Editorial Review: 5/13/2016

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