Sport Definition Essence Selenium is a diet supplement in the form of tablets. The preparation is a supplement containing highly bioavaiable selenium from sodium selenate. Regular use of the supplement contributes to the replenishment of this micronutrient deficiency. Selenium has an antioxidant properties. Thanks to this, it allows you to effectively deal with problems related to oxidative stress. It is linked to improved immune function. Selenium should be used by people who want to improve thyroid function and the condition of the skin and nails.