Assessment of zinc status.

Although the gross skin rash of profound zinc deficiency is well documented in patients with acrodermatitis enteropathica, glucagonoma and severe deprivation, this striking clinical manifestation is rare. Unfortunately, other clinical signs are variable and difficult to assess, and so we seek a quantitative assessment of body Zn stores (Solomons, 1979). There are two different measurements for assessing the status of a trace element or vitamin in the body; namely, either the total body content, or an indirect measure of an appropriate body content. There is, however, little work on directly measuring the total body content of Zn in man, although nearly 40 years ago Widdowson et af. (1951) estimated the content of three adult cadavers. These were of two patients who had died of chronic disease and one emaciated suicide, and so the Zn contents were probably not normal. Nevertheless, the calculated whole-body contents were 0.75, 1.2 and 2.0 g. These macabre studies have not been repeated, but it may be possible to extrapolate less directly from samples of bone and muscle, in which most (90%) of the Zn is contained, after calculating the skeletal and muscle mass. In small animals total content can be obtained directly (Jackson et af. 1982), but in man an indirect measure has to be used. However, demonstration of an estimated body content below normal levels may not indicate deficiency. Thus, in starvation as tissues waste and urinary Zn increases (Elia ef a f. 1984), the body Zn content falls appropriately, and the body is depleted. Deficiency, as indicated by skin rashes or failure to grow. does not occur until refeeding when growth returns and requirements increase, as Golden & Golden (1981) reported for Zn in children with malnutrition in Jamaica, and Paton (1981) for vitamins in adults in Belsen. Deficiency might, therefore, be defined as an inappropriate reduction of whole-body content leading to abnormal physiological or biochemical functions that are reversed simply by supplementation with Zn. Thus, depletion is always associated with deficiency, but not always vice versa. In clinical practice, however, a simple measure is required rapidly and reliably to assess Zn status in an individual. Reduction of the mean levels of groups of patients is useful only for research studies. Many attempts have been made to assess Zn status with static measurement of levels in a body fluid or tissue, but these demonstrate tissue or fluid depletion, which may or may not …