B12 (Cobalamin)
DESCRIPTION:
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.
FUNCTIONS
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.
Vitamin B12 is freely soluble and
therefore lost into cooking water. It is sensitive to strong acid,
alkali and light.
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.
Upper safe level for daily supplementation
= 500µg
Recommended Daily Allowance = 1µg
Vegans:
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.
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.
INTERACTIONS AND
CONTRA-INDICATIONS
There are no contra-indications recorded
for vitamin B12.
Food (µg/100g)
Lamb’s liver 54.0
Pig’s liver 23.0
Beef, lamb, pork 2.0
Fish, white 2.0
Eggs 1.7
Fortified breakfast cereal 1.7
Yeast extract 0.5
Milk 0.4
REFERENCES:
1. 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.
2. Matthews JH. Cobalamin and folate deficiency in the elderly.
Baillieres Clin Haematol, 8;3:679-697, 1995.
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