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Selenium
Selenium is a trace mineral that, while garnering behind-the-scenes attention among health professionals, has remained somewhat secluded from the public eye. Recognition of selenium's importance in human metabolism has possibly been eclipsed over the years by concerns over toxicity or by unfounded fears of carcinogenicity. Although long an enigma, as well as the subject of contradictory findings, selenium is finally emerging as an agent that may play a pivotal role in preventive medicine. In fact, recent studies suggest that selenium offers protection against a wide spectrum of diseases. Current research is placing selenium in a highly favorable light, showing it to have diverse functions in maintaining optimal health. Named after the Greek word for moon, selenium has been associated with immune system enhancement, prostate cancer prevention, heart disease prevention and sperm production and motility.

Selenium and Cancer Prevention
Recent studies have focussed on selenium's role in the prevention of cancer. Selenium was first associated with the treatment of various skin diseases, and a 10-year double-blinded cancer prevention trial, (originally established to determine if selenium could lower the incidence of basal cell and squamous cell skin cancers) serendipitously showed that selenium may actually prevent prostate, colorectal, and lung cancer in people with a history of skin cancer. The study revealed that selenium did not, in fact, prevent skin cancer, however, the results showed that the total cancer incidence was significantly lower in the selenium group than in the placebo group with fewer prostate cancers (13 vs 35), colorectal cancers (8 vs 19), and lung cancers (17 vs 31); and the results also showed that overall mortality was 17% lower in the selenium group vs the control group.

Although results from this 10-year study are compelling, the principal investigators concur that similar trials should be conducted before making any health claims for selenium's role in cancer prevention. A subsequent trial (Journal of the National Cancer Institute, August 19, 1998) conducted by another group of researchers at Harvard University support earlier findings that selenium may reduce the risk of prostate cancer.

Theories on How Selenium May Prevent Cancer
Selenium's anti-cancer mechanisms are not yet well understood, although some researchers believe that selenium may eliminate early pre-cancerous lesions; laboratory tests have shown cancer cells are receptive to selenium-induced cell death. Another theory is that selenium's chemo-protective function may be attributed to its potent antioxidant capabilities. Selenium's immune stimulating effects and its anti-cancer properties may somehow be connected. Working synergistically with vitamin E to stimulate the immune system, selenium is believed to function as a part of the enzyme, glutathione peroxidase, to convert harmful free radicals into less damaging compounds. Selenium may affect enzymatic processes that possibly inhibit the activation of some carcinogens. Selenium may increase the efficiency of DNA repair mechanisms that reduce carcinogenic damage.

Selenium: How Much Should We Get?
Recently (April 2000), a private, nonprofit organization, The Institute of Medicine, which is affiliated with the National Academy of Sciences (a group that sets the nation's Recommended Dietary Allowances for nutrients) convened to review the maximum levels for a series of vitamins and minerals. The panel recommended that the daily intake for selenium should be 55 micrograms for men and women, which is easily achieved in the average U.S. diet. The amount recommended by the group of experts reflects the amount associated with the highest activity of the mineral needed to guard against free radical oxidation. The maximum amount of selenium established as safe is 400 micrograms per day, more than that amount could cause selenosis, a toxic reaction caused by too much selenium that causes hair loss, tooth loss, nail deformities, and dermatological problems. Healthy people, cautioned the scientists, should not exceed upper intake levels of selenium.

The Soil Connection
Although getting enough selenium from the foods we eat is not a problem in this country, there are other parts of the world where selenium intake is an issue. Because the amount of dietary selenium is dependent on the mineral content of the soil in which food is grown, some countries, such as Finland, have fortified their selenium-deficient soil with the mineral. In other parts of the world, scientists have chosen to bypass this method and have advocated the supplementation of drinking water with selenium. And, because the selenium content of soil is highly variable, there are some areas of the world where the soil has too much selenium and a segment of the population has experienced symptoms of selenium toxicity.

Author: Maureen Mulhern-White
Date Published: 04/24/2000
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