Assessing the trace element status of man.

Recent developments in human trace element nutrition have revealed the need for adequate means of assessing trace element status but, with the notable exception of iron, methods remain grossly inadequate. This applies to the detection of clinically significant deficiency states and even more to the detection of minor deviations from optimal tissue reserves. There is a disturbing tendency for over-interpretation of values used in the assessment of trace element status which is often associated with the use of arbitrary ‘cut off’ levels (Beaton, 1986). The objective of the present paper is to review the limitations of available methods, which restrict both the clinical researcher and the application of new findings in clinical nutrition practice. One must bear in mind the circumstances in which we wish to assess trace element status. If this is in a research setting, there may be access to, and time for, techniques that would not be available or applicable on a clinical basis. In a strictly clinical setting, it may be possible to investigate the long-term hospitalized patient more extensively than the ambulatory patient. Our options are especially restricted when the subjects are infants and young children. A particularly demanding challenge is posed by epidemiological investigations, for which there is a major need. Such studies require use of samples that are easy to collect, process, transport, store and analyse in large batches relatively economically. Approaches to the assessment of trace element status that will be considered are: clinical assessment, ‘static’ measurements of tissue concentrations and of indices of body stores (Solomons & Allen, 1983), measurement of ‘functional’ biochemical or physiological indices that require the presence in optimal quantities of a specific trace element, calculations of dietary intake, traditional balance techniques, intestinal absorption and kinetics studies utilizing isotope techniques, and measuring the response to dietary supplementation. The present paper will focus on one example, namely zinc, in order to illustrate the limitations of currently available techniques.