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Selenium
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Selenium is an essential trace mineral trace element that is involved in the defense against the toxicity of reactive oxygen species, the regulation of the redox state of cells and in the regulation of thyroid hormone metabolism.
Selenium activates an antioxidant enzyme called glutathione peroxidase, which may help protect the body from cancer. Antioxidant effects of selenium can also be accounted for by its role in the selenium-dependent thioredoxin reductases. These enzymes reduce intramolecular disulfide bonds and regenerate ascorbic acid from dehydroascorbic acid.
Selenium may also be helpful in preventing a variety of health conditions including cancer.In controlled studies selenium has induced “apoptosis” (programmed cell death) in cancer cells in test tubes and in animals. A clinical study that included over 1,200 people found those participants who were given 200 mcg of yeast-based selenium per day for four and half years had a fifty percent decrease in the cancer death rate compared with the placebo group. However, in the same study, selenium supplementation was associated with a significant increase in the risk of developing one type of skin cancer (squamous cell carcinoma).
While most of us probably don’t get in enough selenium in our diet, deficiencies are rare in developed countries. However, people with AIDS have been reported suffer from a degree of selenium deficiency.
The RDA for selenium for the average adult is approximately 55 mcg per day, however, many doctors recommend an intake of 100 to 200 mcg a day. Selenium supplementation is usually safe, however, taking more than 900 mcg of selenium a day may be dangerous.
Yang GQ, Zhou RH. Further observations on the human maximum safe dietary selenium intake in a seleniferous area of China. J Trace Elem Electrolytes Hlth Dis 1994;8:159–63.
Lu J, Pei H, Ip C, et al. Effect on an aqueous extract of selenium-enriched garlic on in vitro markers and in vivo efficacy in cancer prevention. Carcinogenesis 1996;17:1903–6.
Redman C, Xu MJ, Peng YM, et al. Involvement of polyamines in selenomethionine induced apoptosis and mitotic alterations in human tumor cells. Carcinogenesis 1997;18:1195–200.
Clark LC, Combs GF, Turnbull BW, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. JAMA 1996;276:1957–63. Published erratum appears in JAMA 1997;277:1520.
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