Vitamin B12 - Benefits, Deficiency Symptoms And Food Sources

Alternative name :: Cyanocobalamin and cobolamin

Vitamin B12 is the largest and most complex of all the vitamins. It is unique among vitamins in that it contains a metal ion, cobalt. For this reason, compounds with vitamin B12 activity are referred to as 'cobalamins'. Vitamin B12, isolated in 1948 from liver extract, was the last vitamin to be identified. The structure of this complex vitamin was elucidated in 1955.

Vitamin B12 occurs in several forms. Cyanocobalamin, the form available commercially, is the most stable form. Forms found in body tissues include methylcobalamin, hydroxycobalamin and adenosylcobalamin.

Vitamin B12 is different from most other vitamins in that its only source in nature is microbial synthesis. It is not found in any plant foods, but it is widely distributed in animal tissues.

Absorption of vitamin B12 is unique among vitamins in that it requires an 'intrinsic factor' for absorption. This factor is necessary to carry the vitamin across the walls of the intestine and into the blood stream. In adequately nourished individuals, vitamin B12 is stored in appreciable amounts (approximately 2000mg), mainly in the liver, which typically accumulates a substantial store, some 5 to 7 years worth. There are no known toxic effects from daily oral doses of up to 100mg (100 times the RDA).

Vitamin B12 is slightly soluble in water, stable to heat, but inactivated by light and by strong acids and alkalis. Excessive amounts of vitamin C present in a meal may lead to destruction of vitamin B12. There is little loss of vitamin B12 in food during ordinary cooking procedures.

Functions and benefits of vitamin B12

Vitamin B12 acts as a coenzyme in methylation reactions. Methylation reactions involve the transfer of methyl groups (CH) from one compound to another. Although vitamin B12 performs its methylation task in only two reactions, these reactions are critical in metabolism.

In the first reaction, methylcobalamin acts as a coenzyme in the conversion of homocysteine to methionine. This reaction is accompanied by the conversion of methyl-tetrahydrofolate to tetrahydrofolate. Methionine is an essential amino acid, which participates in the synthesis of DNA and RNA. This reaction also regenerates the active forms of the folate and vitamin B12 coenzymes.

Adenosylcobalamin acts as a coenzyme in the conversion of methylmalonyl-CoA to succinyl- CoA. This biochemical reaction plays an important role in the production of energy from fats and proteins.

Vitamin B12 is also critical to the central nervous system. It maintains the sheath that surrounds and protects nerve fibres and promotes their normal growth. Since vitamin B12 shares a close metabolic interrelationship with folic acid, it is indirectly involved in the formation of RBCs.

Other functions and benefits include its role as an oxygen carrier, metabolizing fat, alleviating neurological disorders, and boosting the immune system.

Daily allowances of vitamin B12

The minimum Recommended Dosage Allowance of Vitamin B12 are :-

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

Rich sources of vitamin B12

The richest sources of vitamin B12 are liver, kidney, milk, eggs, fish, cheese, meats and poultry. Vitamin B 12 is not found in many vegetables; it is available only from sea vegetables, such as dulse, kelp, kombu, and nori, and soybeans and soy products. It is also present in the herbs alfalfa, bladderwrack, and hops.

Deficiency of vitamin B12

Vitamin B12 deficiency is clinically known as pernicious anemia. A deficiency of vitamin B 12 may cause pernicious (destructive) anemia. It may lead to a poor appetite and retardation of growth in children, chronic fatigue, a sore mouth, a feeling of numbness or stiffness, loss of mental energy, and difficulty in concentration.

Deficiency of vitamin B12 also results in neurological symptoms such as numbness and tingling of the arms and legs, difficulty in walking, amnesia, depression, disorientation and dementia, with or without mood swings. The progression of the neurological complications is gradual. Vitamin B12 deficiency is known to damage the myelin sheath covering the nerves in the brain and spinal cord.