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Issue #61 : A-Z of Nutrition: Vitamin B12 (cobalamin)

Vitamin B12 contains cobalt and it is hence known as cobalamin. It is another member of the water-soluble B complex, and is sometimes known as "anti-pernicious" factor after its ability to prevent the condition pernicious anaemia. The absorption of vitamin B12 is dependent on the presence of a certain substance known as "intrinsic factor" in the gastric juices. Vitamin B12 is freely soluble and therefore lost into cooking water. It is sensitive to strong acid, alkali and light.

What does it do?
Vitamin B12 is needed at a very basic level for the synthesis of DNA and hence for cell production - particularly red blood cells. Vitamin B12 also functions in the metabolism of fatty acids, and in maintaining the myelin sheath around nerves.

B12 is needed for synthesis of DNA, metabolism of fatty acids, and maintenance of the myelin sheath around the nerves. It has been investigated for use by MS sufferers.

What are the deficiency signs?
A deficiency of vitamin B12 leads inevitably to the condition pernicious anaemia (a type of megaloblastic anaemia). This is characterised by a fall in the number of red blood cells. Those still produced are irregular in size, but generally too big.

Unfortunately there is an unpleasant twist to vitamin B12 deficiency, in that symptoms of pernicious anaemia can be effectively masked if folic acid intake is inadequate. This can allow vitamin B12 deficiency to progress silently, showing itself eventually in irreversible neurological damage.

Who should supplement?
Vegans and vegetarians may do well to supplement orally with vitamin B12.

This is a suitable precaution because of the absence of this vitamin from plant foods (1).

Pernicious Anaemia:
To treat or prevent pernicious anaemia, vitamin B12 is often injected intramuscularly in large amounts. Through this method, pernicious anaemia has changed from being a fatal to a treatable disease (2).

High levels of vitamin B12 have also been used therapeutically for reasons other than treating pernicious anaemia. Certain mental conditions (especially in the aged) have been seen to be improved with vitamin B12, but there is no hard evidence for this.

Is it toxic?
No toxic effects have been noted with vitamin B12 in man. Injections of as much as 3 mg/day have been used to treat fatigue and various neurological disorders, whereas 1 mg/day has been used to treat vitamin B12-responsive errors of metabolism.

Intake levels: micrograms (µg)
RDA 1µg
Upper safe level for daily supplementation 500µg

Which foods?

Micrograms (µg/100g)

Lamb's liver


Pig's liver


Beef, lamb, pork


Fish, white




Fortified breakfast cereal


Yeast extract





  • Alexander D, Ball MJ and Mann J. Nutrient intake and haematological status of vegetarians and age - sex matched omnivores. Eur J Clin Nutrition, 48;8:538-546, 1994.
  • Matthews JH. Cobalamin and folate deficiency in the elderly. Baillieres Clin Haematol, 8;3:679-697, 1995.

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