Function:
Vitamin B12 (cobalamin) is a general term used to describe
a group of cobalt containing compounds with a particular
structure. It is a cofactor for two enzymes. One enzyme
converts homocysteine to methionine and the other enzyme
helps convert one form of coenzyme A to another form of
coenzyme A, a reaction that is essential in fat and carbohydrate
metabolism.
Recommended
Dietary Allowance:
For
both men and women 2.4 mcg per day. The Institute recommends
fortified foods or a supplement for those over age 50 because
of evidence that up to 30% of the aging population is unable
to absorb vitamin B12 satisfactorily.
Deficiency:
Deficiency results in a sore tongue, numbness and tingling
in the extremities (worse in the legs), weakness, altered
gait, and anemia. Prolonged deficiency can result in irreversible
nervous system damage. People with pernicious anemia are
lacking a stomach factor essential for absorption of B12.
They can develop severe symptoms which if not recognized
result in permanent disability and sometimes death.
Sources:
All
plants, except for certain algae, lack vitamin B12. Meats
and dairy products are the usual source. Ready to eat cereals,
soy and milk supplements are frequently fortified and provide
a rich source for some people.
Toxicity
and UL:
Toxicity
is not seen even with 5,000 mcg per day. No adverse effects
from food or supplements have been documented hence there
is no UL.
