Selenium is an element that is essential in small amounts for the organism's functioning, and its deficiency or excess causes negative health outcomes. Selenium is obtained from dietary sources and performs various physiological functions in the body, especially as selenoproteins. Selenium supports antioxidant defense systems and plays a crucial role in the immune system. It also is involved in the metabolism of thyroid hormones and is an essential element for fertility/reproductive health. Despite its importance, selenium deficiency is still prevalent in the world. The endemic diseases that occur in selenium deficiency are Keshan disease and Kashin-Beck disease. Apart from these diseases, selenium deficiency has been associated with many chronic diseases such as cardiovascular diseases, thyroid diseases, and cancer. This chapter provides insights into the functions of selenium in the organism, its dietary sources, the diseases caused by its deficiency, and its management.
Causes and Management of Nutritional Deficiency Disorders
TopSelenium In Food: Bioavailability And Dietary Sources
Selenium exists in both inorganic and organic forms within the structures of all living organisms. Elementary selenide (Se2–), selenite (SeO32–) and selenate (SeO42–) are among the inorganic forms, while selenomethionine, selenocysteine, methylselenocysteine, selenocystathionine and proteins containing these amino acids are among the main organic compounds. Plants have the capability to absorb and convert both inorganic and organic forms of selenium (Genchi et al., 2023).
The absorption of selenium-containing compounds occurs principally in the duodenum and small intestine. Interestingly, selenium absorption seems independent of an individual's specific selenium requirements. Different chemical forms of selenium utilize distinct absorption mechanisms; for instance, selenite undergoes simple diffusion into cells, while selenate is absorbed through a cotransport mechanism involving a sodium/selenate, OH– antiporter. Factors like sulphur, lead, arsenic, calcium, and iron can hinder selenium absorption (Minich, 2022).
Meat products contain exclusively organic selenium, while plants contain both organic and inorganic selenium (Cámara-Martos et al., 2015). Selenium is converted in plants from selenates to selenomethionine and selenocysteine, whereas products of animal origin contain mostly selenocysteine (Kieliszek, 2019). The selenium content in plant and animal foods varies considerably. The selenium content in plants is contingent upon the bioavailable levels in the soil. The selenium content in animals depends on the diet, the level of selenium in the feed, and the use of supplements. Especially the selenium content of animal feeds is related to the content of the soil (Minich, 2022).