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Home :: Vitamins B12

Vitamin B12 - Benefits, Deficiency Symptoms And Food Sources

Alternative names :- Cobalamin

Vitamin B12 (cobalamin) is an important water-soluble vitamin.The discovery of this vitamin in the United States started with the work of Mary Shrob. Lactobacillus lactis Dorner bacteria required, for their growth, a factor from the liver; and this factor was proportional to the antipernicious anemia activity of the liver extract. This knowledge led others to isolate a crystalline factor in the liver which was effective against pernicious anemia.

Almost simultaneously, in England, Lester Smith was conducting clinical trials with purer extracts of the liver exhibiting antiperniciolls anemia activity. He finally isolated a highly concentrated red substance, vitamin B12, which cured pernicious anemia.

Benefits and functions of vitamin B12

Vitamin B12 primary functions are in the formation of red blood cells and the maintenence of a healthy nervous system. Vitamin B12 is necessary for the rapid synthesis of DNA during cell division. This is especially important in tissues where cells are dividing rapidly, particularly the bone marrow tissues responsible for red blood cell formation.

Adenosylcobalamin is required for the conversion of homocysteine into methionine. When the conversion is deficient, folate metabolism is deranged (methyl tetrahydrofolate is not converted to tetrahydrofolate), causing defect in DNA synthesis and failure in maturation of blood cells. Vitamin B12 also plays a role in converting the body store of methyl folate into its active form, folacin. Adenosylcobalamin is also required for the conversion of methylmalonic coenzyme A to succinyl coenzyme A; its absence leads to large increase in the tissue level of methylmalonic coenzyme A, with abnormal synthesis of fatty acids. These are incorporated in the nervous tissue lipids, causing neurological complications.

Vitamin B12 is also important in maintaining the nervous system. Nerves are surrounded by an insulating fatty sheath comprised of a complex protein called myelin. Vitamin B12 plays a vital role in the metabolism of fatty acids essential for the maintainence of myelin. Prolonged Vitamin B12 deficiency can lead to nerve degeneration and irreversible neurological damage.

Recommended dosage of vitamin B12

The minimum Recommended Dosage Allowance of Vitamin B12 are :-

  • Adults - 2 mcg.
  • Pregnant women - 2.2 mcg.

Deficiency symptoms of vitamin B12

Symptoms of severe vitamin B12 deficiency (regardless of the cause) may include burning of the tongue, fatigue, weakness, loss of appetite, intermittent constipation and diarrhea , abdominal pain, weight loss, menstrual symptoms, psychological symptoms, and nervous system problems, such as numbness and tingling in the feet and hands. Strict vegetarians must remember that they require vitamin B12 supplementation, as this vitamin is found almost exclusively in animal tissues.

Food sources of vitamin B12

Vitamin B12 is synthesized by bacteria in the soil, water, and human and animal intestines. The daily dietary intake is 3-30 micrograms from milk, cheese, eggs, etc. Vitamin B12 in animal foods is available as methylcobalamin, adenosylcobalamin and hydroxycobalamin. Those who live on a pure vegetarian diet in which even milk is excluded (vegans) are in danger of developing deficiency. Gross vitamin B12 deficiency also develops in infants breast-fed by strict vegetarian mothers. .

Vitamin B12 produced by the large intestinal bacteria does not contribute to nutrition because it is not absorbed. Thus, the excretion of vitamin B12 in the feces may be high despite marked deficiency in the body. Small intestinal bacterial activity provides vitamin B12 in vegetarians.


Even with high doses of vitamin B12 no toxicity has been noted, but anaphylactic reaction may occur.

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