The mineral selenium performs many important and essential roles in the human body. One of the major bio-chemical functions of this chemical include anti-oxidation actions at the cellular level, taking part in several enzyme systems, and as a vital component in the maintenance of muscle cell and red blood cell integrity, it also plays a role in the synthesis of nucleic acids - DNA and RNA. This mineral is vital in the detoxification of poisonous metals from the body, it plays a role in cellular respiration and energy transfer reactions, it is also a major player in the production of sperm cells, it plays a part in fetal development and growth, it is also essential in the maintenance of the integrity of keratinous tissues - including the skin, the hair and the nails, it maintains pancreatic functioning, it is involved in the synthesis of antibodies as well as in the production of compounds called the ubiquinones - these chemicals are believed to help in protecting the body against infectious diseases and malignancies, aiding the body deal with inflammatory diseases, chronic heart disease and high blood pressure disorders. Current medical research is focused on the role of selenium as an antioxidant, this is a vital beneficial property possessed by this mineral as oxidative damage to cells and cell membranes is one of the primary causative factors in the majority of disease states and aging related conditions. Selenium was once believed to possess an antioxidant action by actually binding with the freed oxygen, this pathway is similar to the way the vitamin E protects cellular structures and membrane systems. The evidence from recent clinical research points in a different direction and selenium was found instead to be an essential component of the enzyme called glutathione peroxidase, this antioxidant enzyme actively and rapidly degrades hydro-peroxide, the most potent oxidizer molecule in the cells of the human body. The enzyme glutathione peroxidase is actively involved in resisting several disease states in the human body. Medications used in treating disorders like neonatal jaundice, incidences of alcoholic liver disease and blood clotting disorders at times contain low levels of this enzyme. The compound glutathione is also actively involved in protecting cells from oxidation and mutation damage induced by different oxidative and mutagenic agents. Glutathione is also involved in the metabolism of carbohydrates and compounds called prostaglandins. The proper functioning of white blood cells and red blood cells is also dependent on the actions of glutathione peroxidase. Cardiovascular disease is known to be caused by a variety of factors which includes the peroxidation of fats; the remedial actions of glutathione peroxidase in breaking down peroxides found in the fats is helpful in the prevention of such disorders. Many other biological processes also involve the mineral selenium as part of their bio-chemical pathways, the distribution of this mineral is however, not uniform and hence it is not a surprise that at least forty animal species suffer some form of disorders attributable to a deficiency of selenium. Selenium is routinely included as a supplement in most animal feeds in order to prevent the occurrence of these diseases in farm animals. The occurrence of physical symptoms such as calcification and degeneration of muscle tissues and lesion formation in the blood vessels of the heart is observed in farm animals deficient in the mineral selenium. A deficiency of selenium also causes the liver tissues to lose their ability to actively take up oxygen and they die as a result. A selenium deficiency also affects the integrity of the cell membranes and severely compromises the cellular structure - as a result the cellular membranes can turn "leaky ", the cellular fluid that leaks from the compromised cells and membranes accumulates in the tissues. One consequence of this cellular leakage is that many of the intracellular enzymes leak into the blood stream. Male infertility can often be induced due to selenium deficiency; the absence of this mineral in the tissues induces testicular degeneration and results in the active impairment of sperm motility as the first sign of impending infertility. Selenium deficiency can also induce infertility in females, this occurs by way of fetal death and resorption of tissues. The metabolism of the vitamin E actually increases in a human body that has a selenium deficiency; a direct consequence of this situation is an increase in the metabolic requirement for the vitamin in the body of the affected person. The damaging effects of ozone on the pulmonary system are increased in a person suffering from selenium deficiency. Selenium deficiency has also been implicated in oxidative damage to the lungs and eyes of premature infants given oxygen therapy since premature infants generally have lower levels of the mineral selenium then comparable normal term infants of the age groups. The levels of the enzyme glutathione peroxidase and its bio-chemical activity in the body are severely affected by a deficiency of the mineral selenium. Hereditary factors were thought to be responsible for this reduced enzymatic performance at one time - recent research has connected this lowering of enzyme action with low levels of the mineral. Food sources that have the most abundant amounts of selenium are nuts such as Brazil nuts, all organ meats, all seafood, cereals and whole grains as well as brewer's yeast. Selenium is also found in high amounts in special yeasts that are grown on a medium rich in selenium. Selenium in supplemental amounts is supplied by these yeasts - these are normally available in tablet form alone. Supplemental selenium is also available in other forms such as sodium selenite. The most efficiently absorbed source of selenium is yeast with organically bound selenium. Gross deficiencies of selenium are quite rare in western countries, even though most people probably do not take sufficient selenium in the diet. Selenium is deficient in the soils of some areas and a risk of developing a deficiency of selenium exists in people who mainly eat foods grown primarily on selenium deficient soils. Selenium deficiency has also been reported to be evident in individuals affected by AIDS. There is also a clear association between heart disease and depleted levels of selenium according to the evidence from limited research.
Selenium's RDA for average healthy adults is fifty micrograms or 0.05 mg of the mineral per day. It is known that a majority of people have sup-optimal levels of selenium intake in their daily diet - this evidence is based on the results of several epidemiological studies on selenium bio-availability in soils, results from tests of selenium blood levels and studies of levels of glutathione peroxidase. Some normally high selenium foods also become poor sources for the mineral following processing and refining, this is based on results from evaluations of processed foods normally sold in the market. This is true of many of the selenium rich foods; selenium in vegetables for example, can easily be removed by boiling.
There is no question of the safety of selenium at the amounts in which most people normally supplement - about 200 mcg per day. Physical side effects and symptoms such as a persistent skin rash and various changes in the nervous system as well as a loss of fingernails can develop if more than 1,000 mcg of selenium is taken daily. Supplements of selenium have been reported as exacerbating low thyroid functioning if such supplements are taken by a person affected by iodine deficiency induced goiter.