Selenium : Dietary Supplement Fact Sheet
What is selenium?
Selenium is a trace mineral that is essential to good health but required only in small amounts [1, 2]. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent cellular damage from free radicals. Free radicals are natural by-products of oxygen metabolism that may contribute to the development of chronic diseases such as cancer and heart disease [2, 3]. Other selenoproteins help regulate thyroid function and play a role in the immune system [4-7].
What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the world. The content of selenium in food depends on the selenium content of the soil where plants are grown or animals are raised. For example, researchers know that soils in the high plains of northern Nebraska and the Dakotas have very high levels of selenium. People living in those regions generally have the highest selenium intakes in the United States . In the United States, food distribution patterns across the country help prevent people living in low-selenium geographic areas from having low dietary selenium intakes. Soils in some parts of China and Russia have very low amounts of selenium. Selenium deficiency is often reported in those regions because most food in those areas is grown and eaten locally.
Selenium also can be found in some meats and seafood. Animals that eat grains or plants that were grown in selenium-rich soil have higher levels of selenium in their muscle. In the United States, meats and bread are common sources of dietary selenium [9,10]. Some nuts are also sources of selenium.
Selenium content of foods can vary. For example, the U.S. Department of Agriculture Food Composition Database lists the selenium content of Brazil nuts as 544 mcg of selenium per ounce , but values from other analyses vary widely [12, 13]. It is wise to eat Brazil nuts only occasionally because of their very high selenium content. Selected food sources of selenium are provided in Table 1 .