The element that was previously considered to be toxic turned out to be present in the human body in amounts of 10–15 mg, and almost every cell of human body contains it. Very small quantities of selenium are required to maintain proper health in both animals and humans and this selenium must be obtained through dietary sources.
The necessity for selenium is most likely related to its presence in particular proteins termed selenoproteins. There are around 25 selenoproteins in humans and many of these are enzymes that act to protect the body against oxidative damage.
Selenium contributes to growth, supports healthy muscle activity, reproductive organs, reduces the toxicity of certain elements such as mercury, supports the immune system, and even delays the spread of certain viruses such influenza, Ebola, HIV.
The most important role of selenium is its antioxidant effect. This is expressed by the interaction with various enzymes. It plays a key role in the function of the glutathione peroxidase enzyme, which responds to hydrogen peroxide and other harmful lipids and phospholipid hydroxides to prevent harmful free radicals, inhibit DNA damage and the development of metabolic active carcinogens.
Supplementation with selenium, even in “selenium-replete” individuals, has been shown to have marked immunostimulant effects, including an enhancement of proliferation of activated T-cells otherwise known as clonal expansion. Lymphocytes from subjects supplemented with selenium (as sodium selenite) at 200 mcg/day, showed an enhanced response to antigen stimulation and an increased ability to develop into cytotoxic lymphocytes and destroy tumor cells.
The antioxidant effect of selenium can prevent the oxidation of LDL cholesterol, reduce inflammation, strengthen the immune system, help protect the body against oxidative stress, and thereby indirectly reduce HIV virulence.
The pathway for synthesis of the thyroid hormones tetra-iodothyronine (T4) and 3,30 ,50 tri-iodothyronine (T3) highlighting the roles of selenoproteins. The redox protective effects of selenoproteins may be of particular importance in the thyroid gland, whose long-lived cells generate H2O2 (and so also reactive oxygen species [ROS]) required for the synthesis of thyroid hormones.
Selenium has long been recognised in animal husbandry as being essential for successful reproduction.25 Idiopathic miscarriage has been shown to be associated with Se deficiency in veterinary practice26 while in sheep, administration of Se supplements has been shown to prevent early pregnancy loss.
Biological functions of selenium
