An appraisal of the newer trace elements.

For an element to be considered essential it should satisfy three criteria: (1) it must be present in living matter; (2) it must be able to interact with living systems; (3) a dietary deficiency must consistently result in a reduction of a biological function, preventable or reversible by physiological amounts of the element. Ideally, essentiality should be established in more than one species and confirmed in more than one laboratory. Since 1970, vanadium, fluorine, silicon, nickel and arsenic have been shown to meet all the criteria listed above, and evidence from one laboratory has indicated that tin may have an essential biological role in the laboratory rat. A review is presented of the evidence on which the essentiality of these elements has been established and, when known, an indication of their biochemical functions. The possible significance of these 'newer' trace elements to the health of man and animals is discussed.