Selenium

Figure 1. The crystal structure of Selenium.

Selenium is a chemical element with the symbol Se and atomic number 34. Elemental Selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals. Selenium occurs naturally in a number of inorganic forms, including selenide, selenate, and selenite but it is most commonly found as an impurity, replacing a small part of the sulphur in sulfide ores of many metals.

In biology, Selenium is found in the amino acids selenomethionine, selenocysteine, and methylselenocysteine. In these compounds, Selenium plays a role similar to sulphur. In humans, Selenium is a trace mineral. Selenium is an essential component of various enzymes and proteins, called selenoproteins, that help to make DNA and protect against cell damage and infections. Selenoproteins are also involved in the reproduction and metabolism of thyroid hormones.

Selenium within the body is mainly stored in muscle tissue by volume. However, the thyroid gland holds the highest density of Selenium due to various selenoproteins that assist with thyroid function.

Food Sources

The amount of selenium in foods can vary widely depending on the selenium content of the soil in which it is grown. Soil content varies widely by region. Plant foods obtain selenium from soil, which will then affect the amount of selenium in animals eating those plants. Protein foods from animals are generally good sources of selenium. Seafood, organ meats, and Brazil nuts are the foods highest in selenium although Americans obtain most of their selenium from everyday staples, like breads, cereals, poultry, red meat, and eggs.

• Brazil nuts
• Fin fish and shellfish
• Beef
• Turkey
• Chicken
• Fortified cereals
• Whole-wheat bread
• Beans, lentils

The Recommended Dietary Allowance for adult men and women 19+ years of age is 55mg daily. Women who are pregnant and lactating need about 60mg-70mg daily, respectively.

Taken as a Dietary Supplement

Selenium supplements are commonly promoted an an antioxidant, to help lower the risk of certain cancers, to help protect against heart disease, to help prevent mental decline, to help boost the immune system, to help reduce asthma symptoms, and to help maintain optimal thyroid health.

However, the human body requires only trace amounts of Selenium for optimum health. Consuming too much Selenium can be toxic and even fatal. Symptoms of Selenium toxicity include metallic taste, bad breath, hair loss, dizziness, nausea, vomiting, facial flushing, tremors, nail brittleness, nail discoloration, fatigue, irritability, and muscle soreness.