Selenium was discovered as chemical element in 1817 by the Swedish chemist Jöns Jacob Berzelius and named after the Greek moon goddess "Selene". Until the middle of the 20th century, the meaning of selenium for the health of humans had nearly been unknown. Only in 1957 it was recognised that the human organism absolutely needs selenium for life.
Selenium has been confirmed as essential trace element due to the discovery of 25 selenoenzymes so far. Trace element because the body needs selenium in small (µg=microgram) quantities and essential because it is indispensable to life for the body. Since the body's own metabolism cannot build selenium, it is has to be supplied daily in sufficient quantity, at best with nutrition.