Tell me about...
Selenium
What is selenium?
An essential trace element, selenium is nonmetallic, gray
in appearance, and similar to sulfur in its chemical composition.
It is often available in single or multivitamin supplements.
Why do
we need it?
Selenium is needed to activate a number of hormones produced
by the thyroid gland. It also activates an antioxidant enzyme
called glutathione peroxidase, which may help protect the
body from cancer, and has been shown to induce "apoptosis"
(programmed cell death) in cancer cells. Selenium also plays
a vital role in the functioning of the immune system. Studies
have found that selenium supplementation stimulates the activity
of white blood cells. It also enhances the effect of vitamin
E, one of three vitamins that act as antioxidants.
How much selenium should
I take?
According to the National Academy of Sciences, the recommended
daily allowance (RDA) of selenium is as follows:
- Adult men: 55 micrograms/day
- Adult women: 55 micrograms/day
- Children aged 7-10: 30 micrograms/day
- Infants: between 10-15 micrograms/day
- Pregnant/lactating women: between 65-75 micrograms/day
What are some good sources
of selenium?
Brazil nuts are the best source of selenium. Yeast, whole
grains, garlic and seafood are also good sources. Some vegetables
may contain considerable amounts of selenium depending on
the content of selenium in the soil.
What can happen if I don't
get enough selenium?
While most people do not consume enough selenium on a daily
basis, severe deficiency is rare. Soils in some areas are
selenium deficient, and people who eat foods grown primarily
on selenium-poor soils can be at greater risk for deficiency.
The most notable condition caused by selenium deficiency is
Keshan disease, which causes an abnormality of the heart muscle.
Some studies have shown that patients with AIDS have abnormally
low levels of selenium. Other research has demonstrated an
association between heart disease and depleted levels of selenium.
What can
happen if I take too much?
Taking large amounts (more than 1,000 micrograms) of selenium
per day can cause the loss of fingernails, teeth, and hair;
nausea; and fatigue. In conjunction with iodine-deficiency
induced goiter, selenium supplementation has been reported
to increase the severity of low thyroid function.
Other Resources :
The
More You Know About Minerals
The
More You Know About Nutrition
References
• Recommended Dietary Allowances,
10th ed. Washington, D.C.: National Academy Press, 1989.
• Murray M. Encyclopedia of Nutritional Supplements.
Rocklin, CA: Prima Publishing, 1996.
• Clark LC, et al. Effects of selenium
supplementation for cancer prevention in patients with carcinoma
of the skin. JAMA 1996;276:1957-63.
• Peretz A, et al. Lymphocyte response is enhanced by
supplementation of elderly subjects with selenium-enriched
yeast. Am J Clin Nutri 1991;53:1323-28.
• Dworkin BM. Selenium deficiency in HIV infection and
the acquired immunodeficiency syndrome (AIDS). Chem Biol
Iteract 1994;91:181-86.
• Moore JA, Noiva R, Wells IC. Selenium concentrations
in plasma of patients with arteriographically defined coronary
atherosclerosis. Clin Chem 1984;30:1171-73.
• Contempre B, et al. Effects of selenium supplementation
in hypothyroid subjects of an iodine and selenium deficient
area: The possible danger of indiscriminate supplementation
of iodine deficient subjects with selenium. J Clin Endocrinol
Metabol 1991;73:213-15.
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