Although dietary zinc has been known since the 1960s to play an important role in human health, it was not until as recently as 1990 that its role as an important ant-oxidant was identified. Perhaps not surprisingly, early attention focussed on zinc's role as an essential mineral for sexual and reproductive health, particularly in the male; but it is now known that its functions are much more numerous. Indeed some nutritional practitioners go so far as to claim that plentiful supplies of dietary zinc are vital for the proper functioning of every cell in the body.

Initial laboratory experiments appeared to show two ways in which zinc discharged its anti-oxidant functions. The first is that dozens of vital enzymes within the body contain zinc and in these enzymes the zinc molecule acts directly as an anti-oxidant, protecting the biochemical structure of the enzyme from free radical attack. Secondly, zinc acts to stabilise proteins which may otherwise react with highly unstable minerals, particularly iron and copper, to form free radicals.

These experimental demonstrations of zinc's anti-oxidant activity have now been amply confirmed by studies of the effects of zinc deficiencies and supplementation in live humans; and some researchers have given particular attention to zinc's activity within the brain.

Zinc is found in higher concentrations within the brain than any other essential mineral except iron and is believed to be particularly important in preserving the effectiveness of the so-called "blood brain barrier" (BBB). The purpose of the BB is to protect vital brain and nervous system tissue from the toxins which it might otherwise absorb through the blood supply. The potential problem is that the BBB is made of a highly sensitive and fragile membrane, largely comprised of fatty acids, which is particularly vulnerable to the oxidative damage caused by free radicals.

The supposition is therefore that oxidative stress upon the body may lead to reduced effectiveness of the BBB, with a consequently increased likelihood of degenerative health problems within the brain and nervous system; the best known of these being Alzheimer's and Parkinson's disease. This supposition has been borne out by laboratory experiments on rats, which have also shown that zinc deficiency in these animals significantly reduces the strength of the BBB.

It is perhaps not surprising, therefore, that zinc deficiency in humans has long been associated with brain pathologies including schizophrenia, multiple sclerosis, dyslexia, Huntington's disease, various dementias anorexia and depression. The logical corollary of these well-established findings should be that adequate supplies of dietary zinc will protect against these pathologies, perhaps especially those degenerative ones most closely associated with long-term oxidative stress.

Unfortunately, however, it appears that zinc is one of those minerals which it is becoming increasingly difficult to obtain from the daily diet. Soil depletion, environmental pollutants and diets high in refined carbohydrate diets are all implicated in dramatically reducing the amount of zinc active within our bodies; and the problem is especially acute for the elderly, whose less efficient digestive systems often struggle to absorb adequate amounts of the mineral, even supposing that these are present in the diet in the first place.

And these problems are compounded by the fact that the functions of zinc are by no means confined to brain and nervous system health. Adequate zinc is also necessary for the effectiveness of the immune system and wound healing, for reproductive and sexual health, the prevention of degenerative eye disease, the regulation of blood sugar and the maintenance of skin health to name but a few.

Not surprisingly, therefore, nutritional therapists make a strong case for routine zinc supplementation, particularly for the older population, and commonly recommend a daily protective dose of 15-25 mg of zinc per day. Both the US and EU authorities suggest a Recommended Dietary Amount (RDA) of 15 mg, and a good quality multi-mineral product will commonly provide around half this quantity. Higher doses of the single mineral are of course available when required for tackling the conditions detailed above, but more than 200 mg of zinc daily should not be taken for extended periods because this may interfere with the absorption of other minerals.

In this context it should be remembered in any case that the body functions holistically and that all supplements of zinc, of whatever quantity, should be taken together with comprehensive multi-mineral and multi-vitamin preparations.