In contrast to the other water soluble vitamins, cobalamin is stored in the body (~4-5 mg)
Good sources: This vitamin is not found in plants! It is synthesized only by microorganisms. Animals obtain cobalamin from intestinal flora or by eating the meats of other animals. Especially liver, whole milk, eggs, oysters, fresh shrimp, pork, and chicken.
DRI: 1.8-2.4 mg/d
Functions: Essential for 2 enzymatic reactions: synthesis of methionine and isomerization of methylmalonyl CoA that arises from odd fatty acid chains. Cobalamin converts some forms of THF to the active form. If cobalamin is deficient, the inactive forms build up and cannot be converted. Therefore, cobalamin deficiency can resemble folic acid deficiency and vice versa.
Deficiencies: Pernicious anemia. Deficiency is most often due to an inability to absorb the vitamin rather than an inadequate amount in the diet. This disease is often due to an autoimmune attack of the gastric parietal cells which produce intrinsic factor. Intrinsic factor binds to cobalamin and forms a complex that is absorbable. Without intrinsic factor, cobalamin is not absorbed. Vitamin B12 deficiency can also lead to CNS symptoms. Folic acid supplementation can correct the anemia associated with vitamin B12 deficiency but not the CNS effects. Make sure you know which is deficient!
Toxicity: None known