Tell me about...
Vitamin B12
What is
vitamin B12?
Discovered in 1948, vitamin B12 is a water-soluble vitamin
absorbed in the intestines and carried throughout the body
in the bloodstream. Since it is not stored in body fat, after
the body uses what it needs, any excess B12 is excreted via
urine or sweat.
Why do
we need it?
Vitamin B12 is essential for the production of red blood
cells. It plays a role in the metabolization of proteins and
fats and the synthesis of myelin, a fatty substance that encases
nerve fibers. Vitamin B12 also displays some antioxidant properties.
It works with folate to convert the amino acid homocysteine
into methionine, a substance that helps prevent cells from
becoming malignant.
Vitamin B12 injections have also been rumored to increase
energy, although at present, there has been no scientific
evidence to substantiate this claim.
How much
vitamin B12 should I take?
According to the National Academy of Sciences, the recommended
daily allowance (RDA) for vitamin B12 is as follows:
- Adult men: 2-2.4 micrograms/day
- Adult women: 2-2.4 micrograms/day
- Children aged 7-10: 1.4 micrograms/day
- Infants: 0.5 micrograms/day
- Pregnant/lactating women: 2.6 micrograms/day
What are
some good sources of vitamin B12?
The only natural dietary sources of vitamin B12 come from
animal products such as meats, eggs, milk, cheese, yogurt
and fish. Clams and oily fish such as tuna, cod and sardines
are particularly high in B12. Most fortified cereals also
contain high quantities of vitamin B12.
What can
happen if I don't get enough vitamin B12?
While B12 deficiency is rare in young people, the elderly
may have trouble absorbing natural vitamin B12 and require
supplements. Symptoms of B12 deficiency can include memory
loss, instability, disorientation, nerve damage, decreased
reflexes and possible hearing loss. A lack of B12 has also
been linked with increased levels of homocysteine, which in
turn has been associated with heart disease, birth defects
and Alzheimer's disease.
B12 deficiency may also be caused by a genetic defect, in
which a protein known as gastric intrinsic factor is not present
in the body. In such cases, a condition known as pernicious
anemia can develop. The condition must be treated with B12
injections, or neurologic damage may occur.
What can
happen if I take too much?
To date, no reports of toxicity have been associated with
high intake levels of vitamin B12. Because it is water-soluble
and is not stored in the body, the chances of enough B12 building
up to toxic levels are extremely unlikely.
Other Resources :
The
More You Know About Vitamins
The
More You Know About Nutrition
References
• B vitamins may
cut heart disease risk. Harvard Health News April 1998.
• B vitamins and the heart: what men can learn from women.
Harvard Men's Health Watch June 1998.
• Recommended Dietary Allowances, 10th ed. Washington,
D.C.: National Academy Press, 1989.
• The effect of vitamin B12 deficiency on older veterans
and its relationship to health. J Am Geriatr Soc October
1998.
• Vitamin B12 Fact Sheet. American Health, 1999.
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