Essential and toxic trace elements in human health and disease: an update.

Ultratrace elements are those elements with an estimated dietary requirement usually less than 1 mcg/g and often less than 50 ng/g diet for laboratory animals. Elements suggested to fit in the ultratrace category include arsenic, boron, bromine, cadmium, chromium, fluorine, lead, lithium, molybdenum, nickel, selenium, silicon, tin and vanadium. Since the first meeting in 1986 of the International Society of Trace Element Research in Humans (ISTEPH), an increasing number of reports have appeared which describe findings that suggest several of the ultratrace elements are more important in human nutrition than currently acknowledged.