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Vitamins 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.
STABILITY
Vitamin B12 is freely soluble
and therefore lost into cooking water. It is sensitive to
strong acid, alkali and light.
DEFICIENCY
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.
REQUIREMENTS
Upper safe level for daily
supplementation = 500µg
Recommended Daily Allowance
= 1µg
SUPPLEMENTAL USES
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.
SAFETY
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 SOURCES
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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