Selenium

Selenium is a non metallic chemical element, member of the group XVI of the periodic table. In chemical activity and physical properties it resembles sulfur and tellurium. Selenium appears in a number of allotropic forms: the most popular are a red amorphous powder, a redcrystalline material, and a gray crystalline metal like form called metallic selenium.

This micro mineral is needed in the diet on a daily basis, but only in very small amounts (50 micrograms or less). The other micro minerals that all humans must get from food are arsenic, boron, cobalt, copper, chromium, fluorine, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc.

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While the nutritional value of all plant food depends on the soil in which it was grown, the selenium content of plants seems particularly sensitive to soil concentrations.

What are the health effects?

Short-term: Selenium is an essential nutrient at low levels. However, EPA has found selenium to potentially cause the following health effects when people are exposed to it at levels above the MCL for relatively short periods of time: hair and fingernail changes; damage to the peripheral nervous system; fatigue and irritability.

Long-term: Selenium has the potential to cause the following effects from a lifetime exposure at levels above the MCL: hair and fingernail loss; damage to kidney and liver tissue, and the nervous and circulatory systems.

The exposure to selenium mainly takes place through food, because selenium is naturally present in grains, cereals and meat. Humans need to absorb certain amounts of selenium daily, in order to maintain good health. Food usually contains enough selenium to prevent disease caused by shortages.

What is the function of selenium?

Deficiency Symptoms

Deficiency symptoms for selenium clearly center around two of the body areas where oxidative stress is known to take its toll: the heart and the joints.

With respect to the heart, there is actually a specific disease, called Keshena disease, which can be prevented by increased intake of selenium. This disease involves heart arrhythmias and loss of heart tissue. With respect to the joints, there is also a specific disease, called Kashin-Beck's disease, in which selenium deficiency has been determined to be a primary contributing cause. This disease involves deterioration of the joint tissue.

Toxicity Symptoms

Nausea, vomiting, hair loss, skin lesions, abnormalities in the beds of the fingernails, and fingernail loss can all be symptomatic of selenium toxicity. Levels of selenium necessary to trigger these toxicity symptoms aren't usually obtained from food, since selenium-rich foods contain about 30-50 micrograms of selenium per serving.

Drug-Nutrient Interactions

What medications affect selenium?

Glucocorticoids are a widely-used family of anti-inflammatory drugs based on a prototype substance called cortisol. In the United States, cortisol-based anti-inflammatory drugs are available under 70 different brand names. Many of these medications are based on one of the three major cortisol subtypes that consist of prednisolone, dexamethasone, and triamcinolone. All of these medications can reduce the body's supply of selenium.

Nutrient Interactions

Selenium is indirectly responsible for keeping the body's supply of at least three other nutrients intact: these three other nutrients are vitamin C, glutathione, and vitamin E. Although the chemistry of these relationships is complicated, it centers on an enzyme called glutathione peroxides. This enzyme cannot function without selenium.

Health Conditions

Selenium may play a role in the prevention and/or treatment of the following health conditions:

Form in Dietary Supplements

Selenium can be purchased as a dietary supplement in one of two basic forms: chelated or non-chelated. "Chelated" means connected with another molecule. In the case of selenium, the most common chelates fall into the category of amino acid chelates. The most widely-available are selenomethionine and selenocysteine. Supplemental selenium is also available in non-chelated form. Here the most widely available choices are sodium selenate and sodium selenite.

Food Sources