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Selenium

Selenium is an essential mineral found in trace amounts in the human body. It works as an antioxidant, especially when combined with vitamin E, by scavenging damaging particles in the body known as free radicals.While most people probably don't take in enough selenium, deficiencies are rare in Western countries. Soils in some areas are selenium-deficient and people who eat foods grown primarily on selenium-poor soils are at risk for deficiency. Cigarette smokers have lower levels of selenium, as tobacco decreases absorption of selenium. Many smokers also have poor dietary habits and eat fewer foods containing selenium. Alcohol also lowers selenium levels.Selenium works as an antioxidant, especially when combined with vitamin E, by scavenging damaging particles in the body known as free radicals. These particles occur naturally in the body but can damage cell membranes and possibly contribute to the aging process. Antioxidants such as selenium can neutralise free radicals and may reduce or even help prevent some of the damage they cause.

Selenium is needed for the proper functioning of the immune system and for the production of prostaglandins (substances that affect blood pressure and inflammation in the body). Low levels of selenium may worsen atherosclerosis (plaque buildup in arteries which can lead to heart attack and/or stroke) and can lead to premature aging.

A double-blind trial that included over 1,300 people found those given 200 micrograms (mcg) of yeast-based selenium per day for 4-5 years had a 50% drop in the cancer death rate compared with the placebo group [1]. Another study found that men consuming the most dietary selenium developed 65% fewer cases of advanced prostate cancer than did men with the lowest levels of selenium intake [2]. Selenium supplementation has been found to stimulate the activity of white blood cells, which play a vital role in maintaining the strength of your immune system.
The Recommended Dietary Allowance for most adults is 55 mcg per day, an adult intake of 100-200 mcg of selenium per day is recommended by many doctors. Selenium is safe at the level people typically supplement (100-200 mcg). However, taking more than 900 mcg of selenium per day has been reported to cause adverse effects in some people [6]. Brazil nuts are the best source of selenium. Yeast, whole grains, and seafood are also good sources.Selenium is unlikely to lead to any dramatic improvements in exercise performance. Nor will it have a noticeable impact on muscle growth or fat loss. However, optimal intake of selenium, in conjunction with other vitamins and minerals, is important for anyone who is healthy and wants to keep their immune system strong. Research has reported an association between heart disease and depleted levels of selenium [4]. People who are deficient in selenium also have an increased risk of developing certain types of rheumatoid arthritis [5].Selenium may be taken as part of a vitamin-mineral supplement or as an individual supplement. Selenium enhances the antioxidant effect of vitamin E, so the two should be taken together. Selenium and zinc supplements may also boost your immune system and improve resistance to infections.

1. Clark LC, Combs GF, Turnbull BW. (1996). Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. Journal of the American Medical Association, 276, 1957-1963
2. Yoshizawa K, Willett WC, Morris SJ. (1998). Study of prediagnostic selenium levels in toenails and the risk of advanced prostate cancer. Journal of the National Cancer Institute, 90, 1219-1224
3. Yu S-Y, Li W-G, Zhu Y-J. (1989). Chemoprevention trial of human hepatitis with selenium supplementation in China. Biol Trace Element Res, 20:15-20
4. Moore JA, Noiva R, Wells IC. (1984). Selenium concentrations in plasma of patients with arteriographically defined coronary atherosclerosis. Clin Chem, 30, 1171-1173
5. Knekt P, Heliovaara M, Aho K. (2000). Serum selenium, serum alpha-tocopherol, and the risk of rheumatoid arthritis. Epidemiology, 11, 402-405
6. Yang GQ, Zhou RH. (1994). Further observations on the human maximum safe dietary selenium intake in a seleniferous area of China. J Trace Elem Electrolytes Hlth Dis, 8, 159-165

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