[Trace elements: biological role and nutritional aspects for humans].
The methodological approaches generally adopted to ascertain the essentiality of trace elements present in human beings at levels of the order of magnitude of 1 micrograms g-1 or less are illustrated. An element is recognized as essential when it has a well defined function (as stabilizer, structural, hormonal or as enzymatic cofactor) and when it is always present in tissues and organs in well defined concentration ranges, when it induces reproducible physiological effects, when it is possible to prevent and treat consequences due to its deficiency by its supplementation. For the trace elements Co, Cr, Cu, Fe, I, Mn, Se and Zn a short summary of their biological functions in humans is presented. In particular, for each element an account is given of the mean total quantity accumulated by the human body, the distribution in the main organs, the most important pathways for their uptake and the recommended daily intake. These last values obviously do not take into consideration the synergic or antagonist action due to the intake of other substances that very often can modify the absorption and the metabolism of the element considered.