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Selenium is a trace mineral with potent antioxidant properties. Most of this effect derives from selenium's essential role in the action of a body enzyme called glutathione peroxidase This enzyme detoxifies potentially dangerous peroxide free radicals, which have been linked to
everything from cancer to heart disease. Stored mainly in the liver and kidneys, selenium is often associated with vitamin E, and some scientists even suggest that selenium acts as a "stand-in" antioxidant when vitamin B is lacking. In addition to its antioxidant qualities,
selenium is involved in connective-tissue (e.g., joints, ligaments and tendons) synthesis and appears to play a role in the function of prostaglandins, which are fat- derived hormonelike substances.
A recent highly publicized study from Arizona found that dietary intake of selenitim had an inverse relationship to the development of several types of cancer. Most likely, this finding relates to the antioxidant activity of the mineral, since rampant free radicals are thought to cause the initial cell mutations that are the genesis of most cancers. A less-well-known aspect of the mineral concerns its role in thyroid-hormone synthesis. As most bodybuilders know, the thyroid gland, located in the neck, secretes hormones that control the body's metabolism.
Selenium intake can either boost or inhibit thyroid-j hormone synthesis, depending on certain existing conditions. The thyroid gland produces two main hormones: thyroxine (T4) and the more active triiodothyronine (T). Most of the conversion of T, to T, occurs in the liver, under the influence of an enzyme called type-I deionidase, which works by slicing an iodine molecule off T4, thus turning it into T3. Selenium activates the liver's thyroid-converting enzyme. However., the presence of larger amounts of the mineral has reverse effect; that is, it causes decreased thyroid activity, hypothyroidism. This is particularly true if another trace mineral needed for thyroid synthesis, iodine, also lacking in the diet, Iodine forms one-third of thyroid hormone content, with the other two thirds being the amino acid tyrosine.
Some selenium is stored in the body. The recommended daily allowance for the trace mineral is 70 micrograms (mcg) for men and 55 mcg for women, and most researchers who study minerals suggest consuming no more than 500 mcg a day. An average diet supplies 35- 60 meg a day, with seafood being the richest food source of the mineral. Taking vitamin C with a supplemental form of selenium called sodium selenite will decrease absorption of the mineral, but this doesn't occur with other forms of selenium, such as those bonded to the amino acid methionine: While you want to ensure an adequate intake of selenium through either food or supplements, you don't want to go overboard with this particular nutrient. Taking it in excessive amounts will lead to side effects that include garlic breath, fatigue, nausea, abdominal pain, diarrhea, red discoloration at the base of your nails, hair loss and infertility.