Selenium (78,96 a.m.u.) – vital macronutrient. Essential for normal thyroid function and normal functioning of immune, reproductive, cardiovascular and nerve systems. More than 30 biologically active selenium-containing proteins are reported. Glutathione peroxidase enzyme includes selenium (enzyme in body protection against damaging effect of active oxygen forms) and iodothyronine deiodinase (enzyme transforming non-active thyroxin (T4) enzyme into active 3-iodothyronine (T3)). Selenium is functionally bond with E vitamin. Selenium compounds as natural anti-oxidant are used for prevention and treatment of many diseases, but in dermatology and cosmetology experts are using medicated selenium-containing shampoos, soaps, gels and creams.

Selenium is similar to mercury regarding biochemical features. Selenium is able to replace mercury in cysteine; this is why selenium-cysteine is a special amino acid with special features. Selenium is intaken with food, mostly as selenium methionine of plants, which are absorbing this micronutrient from soil. Concentration of selenium in blood serum and other biological liquids varies depending on concentration of selenium in food and water. In blood plasm approx. 50 – 60% of selenium is bond with selenium protein P, approx. 30% is constituting glutathione peroxidase, but the remaining selenium is associated with albumin. In body selenium is partly transferring into dimethyl selenium and excreted through lungs. Main ways of selenium excretion are kidneys with urine.

Selenium level in plasm is decreasing during the acute body response level to irritation or infection. Selenium deficit could be caused by the lack of it in food and by disorders in diet or digestion. Indicative deficiency of selenium could be caused by Keshan disease – endemic cardiomyopathy, peculiar to Keshan region in China. This region is famous of deficiency of selenium in soil. Together with other factors, selenium makes a solid contribution to the Kashin-Beck disease – multiple lesions of joints, caused by mineral balance disorders. This endemic disease is described in China and could be also caused by artificial feeding with low concentration of selenium. Even a small deficiency of selenium could lead to changes of thyroid, immune and reproductive systems and could also cause psychic disorders.

Selenium deficit is reported in cases of pathogenesis of cardiovascular diseases, increase of virulence of viruses, decrease of bodily defence from some kinds of cancer.

Overdoses of selenium could be toxic. Symptoms of intoxication with overdoses of selenium could be indicated in appearance of garlic smell in outbreath and of urine, metallic taste, headaches, sickness, loss of hair and damage of nails. Loss of sensibility, spasms, pneumonia, pulmonary oedema, cardiovascular collapse.

Cases of selenium intoxication were reported not only in cases of exposition to selenium, related to the manufacturing, but also in cases of self- prescription. Investigation of serum or plasm could quite precisely indicate the status of selenium in body and adequacy of last intake (in case ow awareness of changes in the setting of acute phase response).

To assess the level of selenium toxicity it is reasonable to investigate 24-hour urine. Concentration of selenium in it depending on geography source of intaken food could vary from 20 up to 1000 mcg/l.

Investigation of selenium in hair is recommended to assess the long-lasting intake of selenium. It shall be mentioned that medicated shampoos and other haircare products could contain selenium and cause external soiling of specimen.