Selenium (Se, Latin for selenium) – a chemical element from the group of non-metals in the periodic table. A dozen or so of its isotopes in the mass range 65–91 are known, of which 6 are stable.

This element was discovered in 1817 by J.J. Berzelius. The name comes from Selene (Greek: Σελήνη), the Greek name for the moon and the goddess who personified him. Berzelius called him that because he always appears with tellurium, whose name derives from tellus, meaning Latin for “Earth.” At the same time, he wanted to emphasize in this way that selenium is not “from the same earth” as tellurium and has different properties from it.

Biological significance
Selenium is one of the essential micronutrients and must be supplied in food. The content of selenium in food products varies significantly, which is associated with large differences in the content of selenium in soil and water in different parts of the world. Soils in Poland are considered low in selenium.

Sources of selenium in food: cereals, meat, eggs, dairy products, fish and crustaceans. Not all foods are a good source of selenium, because this element is not well absorbed in the digestive tract in every form. The chemical form of selenium plays a key role in bioavailability. Selenium obtained from yeast is characterized by the highest bioavailability. Absorption of selenium is enhanced by small molecular proteins and vitamins (mainly A, E, C). The synergistic effect of selenium with vitamin E contributes to delaying the aging process and accelerating cell regeneration.

It is necessary for the proper functioning of enzyme systems. Its most important function is to create a powerful antioxidant, an enzyme called glutathione peroxidase. It protects red blood cells and cell membranes against the harmful effects of free radicals. Maintaining an adequate level of selenium is important in sleep apnea syndrome, where oxidative stress may occur.

It is also important for the functioning of the immune system and thyroid. Along with other antioxidants, it protects the heart against free radicals, helps in the fight against depression, fatigue and excessive nervousness. Reduces the amount of harmful compounds contributing to the formation of rheumatoid arthritis – administration of selenium relieves the symptoms of the disease in up to 40% of patients.

In men, half of the selenium accumulated in the body is found in the testes and sex glands, as well as in the semen they produce, thus affecting the maintenance of men’s sexual performance.

Selenium prevents the formation of cancerous lesions in various organs and tissues. Numerous studies confirm that selenium reduces the risk of all cancers, in particular liver, prostate, colorectal and lung cancer. Selenium supplementation is very important for smokers who are particularly at risk of lung cancer, because selenium reduces the risk of lung cancer for smokers. To confirm the role of selenium in preventing cancer, an international group of researchers from Denmark, Sweden and the United Kingdom is conducting a large-scale randomized study called ‘Prevention of Cancer by Intervention with Selenium’.

In the United States, the Food and Drug Administration has allowed manufacturers of selenium supplements to give health indications that “selenium supplementation may reduce the risk of certain types of cancer.” Her daily selenium intake is 55 micrograms for adults.

The need for selenium supplementation occurs in smokers, in inhabitants of areas poor in selenium, in persons remaining on total parenteral nutrition (pareneteral), people with severe damage to the function of absorption of nutrients (e.g. Crohn’s disease, the condition after removal of a significant part of the small intestine). Dietary supplement with selenium is recommended for the treatment of cardiovascular diseases, infertility, pancreatitis and asthma. In addition, epidemiological studies have confirmed that reduced selenium intake may be one of the significant factors that increase the risk of cancer in humans.
An excess of selenium is harmful and it is thought that exceeding the dose of 400 micrograms per day can lead to symptoms of poisoning. However, the risk of overdose when using natural selenium preparations is small (doses of up to 800 µg per day have not proved to be toxic).

A deficiency of selenium contributes to limiting the efficiency of the immune system and in some cases to intensifying the progression of the disease. Selenium deficiency is also found in rheumatoid arthritis. The prevalence of the symptoms of selenium deficiency in the general population is a consequence of the insufficient supply of selenium in the diet, which results from the low content of this element in soil in some areas of the earth (also in Poland, as Poland belongs to countries with low selenium content in soil). Deficiency is manifested by enlargement and heart failure, as well as symptoms of goiter and hypothyroidism. It also makes the body more susceptible to the effects of carcinogens. Deficiency in pregnant women can cause irreversible fetal changes, increases the risk of developing heart and liver disease.