Vitamins, Minerals and Dietary Supplements

What is selenium? Why do we need it?

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.

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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.