General Description
Vitamin B-12, also known as cobalamin, cyanocobalamin, and hydroxycyanocobalamin,
is a water-soluble vitamin in the B-complex vitamin group. The B
vitamins are used by the body as coenzymes. They are essential for
maintaining the skin, hair, liver, and good muscle tone in the gastrointestinal
tract. The B vitamins also help metabolize carbohydrates, proteins
and fats. Vitamin B-12 was discovered as a result of attempts to
treat anemia. In 1926, scientists discovered that eating liver once
a day could reverse anemia. By the late 1940s, cobalamin was isolated
as the active ingredient in the liver that effectively controlled
the anemia.
Food sources
Cobalamin is found in foods such as beef, swiss and blue cheese,
clams, eggs, liver, and milk. It is not found in vegetables. Vegans,
strict vegetarians who avoid dairy products, are at high risk
of becoming cobalamin deficient.
Health applications
Functions and uses
Cobalamin is involved in forming nucleoproteins and red blood cells,
and in the functioning of the nervous system. It is involved in
cell activity, DNA replication, and the production of the mood-affecting
substance called SAMe (S-adenosyl-L-methionine). B-12 deficiency
results in a wide array of symptoms such as anemia, general fatigue,
indigestion, depression, and dementia.1
Homocysteine
Most of the health benefits provided by cobalamin relate to its
role in controlling plasma homocysteine levels. High blood homocysteine
levels may contribute to atherosclerosis,2,3,4,6
cardiovascular diseases,2,5,7 thrombosis,6
depression,8,9,10 and possibly Crohn's disease.3,12
Studies indicate that cobalamin can reduce plasma homocysteine
levels and that this action is enhanced by the inclusion of folic
acid.2,4,5,6,7,11
Pernicious anemia
Pernicious anemia in the elderly (and sometimes in alcoholics)
often results from an inability of the stomach to produce glycoprotein,
which aids in the absorption of cobalamin. As is sometimes true
for strict vegetarians, it also results from an inadequate diet.
Symptoms of pernicious anemia include weight loss, weakness, pale
skin and psychological disturbances. Treatment with cobalamin
effectively controls and eliminates pernicious anemia.13,14,15
Dosage/Toxicity
On average, dietary intakes of cobalamin are sufficient.4
In cases of elevated homocysteine levels, doctors usually prescribe
cobalamin supplementation through injection, tablet, or capsule
form. Cobalamin is also often available as a constituent of multivitamin/mineral
preparations. The RDA recommendation of vitamin B-12 for adults
is 2 mcg per day. The therapeutic range varies from between 100
to 1,000 mcg. There is a very low incidence of vitamin B-12 toxicity,
even in intakes of up to 1,000 mcg per day.
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