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Zinc is one of the so-called trace elements present in the body, but in nature it is present in the Earth’s crust to the extent of about 0.02% and is 23rd in the order of abundance of the elements. In this context it is far scarcer than many elements which are less familiar to biologists today (e.g. zirconium, vanadium or strontium). That zinc is essential for normal life in both humans and animals is now beyond doubt, having been first shown to be required for normal growth in rats and mice in the 1930s (Todd et al. 1934; Bertrand and Bhattacherjee 1935).

This final chapter is not intended to provide a comprehensive overview of the topics discussed previously. Instead it will highlight those topics for which a better understanding is essential before the significance of zinc for human health and wellbeing can be fully assessed. It will also consider some troublesome controversies.

The very large number of indices that have, from time to time, been evaluated, promulgated and, with experience, discarded as methods of assessing the zinc status of a subject is true testimony to the difficulties involved (Solomons 1979; Kirchgessner and Roth 1981; Golden and Golden 1985). None of the methods currently used can be recommended, with the possible exception of the monitoring of responses to zinc supplementation with plasma zinc estimation in conjunction with clinical evaluation.