The importance of diet composition in ultratrace element research.

This review indicates that the lack of appreciation of, information about or understanding of the importance of diet composition has had a major influence on the development of knowledge about 11 ultratrace elements in nutrition. Inappropriate trace element supplementation and inadequate or unbalanced diets probably were responsible for many of the reported inconsistent and divergent findings, and thus, for the resultant controversy regarding the essentiality of specific ultratrace elements. Vanadium and nickel are taken as examples, and evidence is presented that variations in the concentrations of dietary components can affect the response of experimental animals to the various ultratrace elements. Furthermore, there is evidence that the ultratrace elements, given in sufficient quantity, can evoke pharmacological responses in animals. Failure to recognize these phenomena probably has led to a number of incorrect or biased interpretations of experimental results. Future research on the importance of ultratrace elements in nutrition requires close attention to an often neglected experimental variable--diet composition.