It is also known as extrinsic factor of castle. It is a water-soluble vitamin.

In 1948 Smith and Parker isolated cyanocobalamin from the liver. In 1955 its complex structure was determined.

It is a complex organo-metallic compound with a cobalt atom. Vitamin B12 cooperates with folate in the synthesis of DNA, so deficiency of either leads to megaloblastosis.

It contains cobalt, therefore it is also known as cobalamin. It is mainly synthesised by bacteria and is found primarily in meat, eggs and dairy products. There has been considerable research into proposed plant sources of vitamin B12. Fermented Soya products, seaweeds, and algae such as spirulina have all been suggested as containing significant B12. However, the present consensus is that any B12 present in plant foods is likely to be unavailable to humans and so these foods should not be relied upon as safe sources. Vitamin B12 is necessary for the synthesis of red blood cells, the maintenance of the nervous system, and growth and development in children. Deficiency can cause anemia. Vitamin B12 neuropathy, involving the degeneration of nerve fibres and irreversible neurological damage, can also occur.

Sources of vitamin B12

Good sources are liver, kidney, meat, fish, eggs, milk and cheese.

Vitamin B12 is not found in foods of vegetable origin. Bacteria in colon also synthesize it. Unlike folic acid, vitamin B12 is heat stable. Liver is the main storage site of vitamin B12. About 2 mg are stored in the liver and another 2 mg elsewhere in the body. These stores are sufficient to fight against any deficiency for one to three years.

Good sources of vitamin B12 for vegetarians are dairy products or free-range eggs. ½ pint of milk (full fat or semi skimmed) contains 1.2 µg. A slice of vegetarian cheddar cheese (40g) contains 0.5 µg. A boiled egg contains 0.7 µg. Fermentation in the manufacture of yoghurt destroys much of the B12 present. Boiling milk can also destroy much of the B12.

Vegetarians are advised that they should ensure their diet includes foods fortified with vitamin B12. A range of B12 fortified foods are available. These include yeast extracts, Vecon vegetable stock, veggie burger mixes, textured vegetable protein, Soya milks, vegetable and sunflower margarines, and breakfast cereals.

This vitamin is found in the fungus Streptomyces griseus. Hence vitamin B12 is obtained as a by-product in the manufacture of Streptomycin.

Absorption takes place from the ileum. Intrinsic factor present in the normal gastric juice is essential for the proper absorption of vitamin B12. It is stored in the liver. From the liver it passes to the bone marrow and helps in the maturation of the red cells. Vitamin B12 is excreted in the faeces and urine.

Benefits of vitamin B12

Essential for the formation and maturation of red blood cells. Vitamin B12 is Castle’s extrinsic factor, which combines with the intrinsic factor present in the normal gastric juice and is absorbed. 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. If B12 deficiency occurs, DNA production is interrupted and abnormal cells called megaloblasts occur. This results in anaemia. Symptoms include excessive tiredness, breathlessness, listlessness, pallor, and poor resistance to infection. Other symptoms can include a smooth, sore tongue and menstrual disorders. Anaemia may also be due to folic acid deficiency, folic acid also being necessary for DNA synthesis.

It increases the white cell count and the platelets through its action in the bone marrow.

Concerned with the maintenance of normal health and activity of certain parts of the nervous system. Vitamin B12 not only cures the pernicious anaemia, but also the neurological manifestations of pernicious anaemia, e.g. sub acute combined degeneration of the spinal cord.

Formation of lipid from carbohydrate in influenced by vitamin B12. Hyperglycemia due to vitamin B12 deficiency can be corrected after administration of vitamin B12.

It also maintains the integrity of the epithelial cells especially of the mouth and the stomach.

It favors the normal growth and is particularly useful in premature babies: the action is probably due to an adequate absorption of metabolic products by influencing the intrinsic factor of Castle formed in the gastric mucous membrane.

It is essential for maintaining the functional integrity of the myelinated fibres of the central nervous system and the peripheral nerves.

It happens to correct or prevent fatty infiltration of the liver by favoring formation of methionine and protecting the liver from injury by certain toxic agents.

Deficiency signs

Due to deficiency of vitamin B12 pernicious or macrocytic or megaloblastic anaemia is produced.

Its deficiency also causes hyperglycemia.

Growth is retarded, nervousness and irritability is also observed.

Deficiency might occur as a result of lack in diet, lack of intrinsic factor as in pernicious anaemia, defective absorption due to intestinal disease, infection with microorganisms, which have affinity for vitamin B12 and thus destroy it in the intestinal tract.

Other important features in vitamin B12 deficiency in man are mucosal atrophy and inflammation of tongue, mouth etc., degenerative lesions of the posterior and lateral columns of the spinal cord. The patient may feel pain, tingling and numbness in the extremities and there may be partial paralysis.

Dietary deficiency of vitamin B12 occurs in subjects who are strict vegetarians and eat no animal products.

Daily requirement:

The requirement is very small.

a) Normal adults 1mcg

b) Pregnancy 1.5 mcg

c) Lactation 1.5 mcg

d) Infants and children 0.2 mcg

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