Secondary Deficiency

Zinc deficiency develops in some people with cirrhosis, malabsorption syndromes, sickle cell anaemia, conditions of increased zinc loss, such as severe burns or major surgery, chronic diarrhoea or diabetes, HIV and AIDS, and during prolonged parenteral nutrition (Prasad et al 1999). Additionally, strenuous exercise and elevated

ambient temperatures increase zinc losses through perspiration. A congenital disorder known as acrodermatitis enteropathica causes severe zinc deficiency.

Clinical note— Measuring zinc status is difficult

Currently, there is no universally accepted single measure of zinc status in humans. The most commonly used approach is the measurement of serum zinc levels, but this is a poor measure of marginal zinc deficiency because zinc is primarily found intracellular^ and only a small portion is found in the circulation where it is mainly bound to plasma protein. Plasma zinc levels are affected by the homeostatic system and other factors, such as diurnal rhythm, stress, infection, starvation and plasma protein levels. As a consequence, it is not an accurate reflection of dietary zinc intake or true zinc status (Wood 2000). Estimation of hair zinc levels is another tool used, with low hair zinc levels indicative of zinc depletion. This method is costly and also subject to inaccuracies caused by variable hair growth and the presence of zinc in some shampoos. The zinc taste response test (also known as the Bryce-Smith taste test) is a popular measure among naturopathic practitioners. It relies on patients detecting a taste after oral administration of 10 ml_ of a zinc sulfate solution. Delayed taste perception or lack of taste is seen to indicate a zinc deficiency state. It is based on the theory that sense of taste is primarily influenced by the zinc dependent enzyme, gustin, in the saliva. As such, low zinc status should substantially affect taste discrimination. This method is not particularly accurate and hampered by variations in patients' subjective sense of taste and the fact that agents other thans zinc influence taste perception. Clinical studies with zinc taste tests have confirmed the inconsistency of the results (Birmingham et al 2005, Garg et al 1993, Mahomed et al 1993). Ultimately, this leaves the diagnosis of marginal deficiency up to a practitioner's clinical suspicion.

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