Scot. meel. J., 1975, 20: 101

ZINC IN CLINICAL NUTRITION

urinary zinc loss so that unless zinc is deliberately added to the dietary regime, some There is some similarity between the nutridegree of tissue depletion is inevitable. The tional aspects of zinc and some other minor total body zinc content is around 30 to 35 elements such as magnesium and phosphorous. For although of undoubted biochemical mmol of which some 20 per cent is in importance, the place of these substances in bond and not readily available. Although clinical nutrition is uncertain. In part, this some authors do recommend the addition of may be due to the fact that the signs and zinc in parenteral feeding only basal requiresymptoms of their deficiency are not well mentsare usually considered (Wretlind, 1972). described and to the feeling that most mixed It would seem best to estimate the actual diets will adequately supply the daily require- losses occurring as a guide to replacement ments. However, it is clear that there can be therapy. The clinical presentation of zinc an increased need for these and other trace deficiency can include a loss of taste sensasubstances because an effect of disease and tion, reduced resistance to infection, poor injury is to alter distribution within the body wound healing, and persistent hypoproteinwhich can in turn lead to an excessive loss in aemia. Infusions of substantial amounts (~1.5 mmol zinc/day) of zinc aspartate is excreta. claimed to improve a previously resistant Many zinc metallo-enzymes are now hypoproteinaemia in severely ill patients known and among their numerous functions (Fodor, 1972). is a part in the regulation of nucleic acid Abnormalities of zinc metabolism are now and protein synthesis. Accordingly, the biological consequence of zinc deficiency is reported in a wide range of otherwise una failure of normal growth and development. related diseases. It seems probable that many This fact is of established economic import- processes can alter the transport of zinc by ance in agriculture and animal husbandry, plasma proteins. Normally the greatest proand human zinc deficiency is increasingly portion of plasma zinc is associated with recognised (Halsted, 1974). The best known albumin (~60%) and this loosely bound zinc examples are associated with the malabsorp- is in equilibrium with a much smaller amount tion of dietary zinc, probably due to the (~1-5%) of molecular complexes of zinc phytic acid content of a mainly cereal diet, with amino acids or other low molecular which causes a complex syndrome involving weight substances. The rest of the plasma dwarfism, hypogonadism and anaemia. Diet- zinc is associated with an oc 2 macroglobulin ary supplements of zinc appear to specifically fraction, which may well have an important reverse these effects. More recently, it has physiological role in zinc transport but does been observed that zinc as well as other trace not seem to alter significantly in disease. The release of products of tissue breaksubstances must be added to the synthetic amino acid diets used in the management of down during the catabolism of protein after phenylketonuric children if a satisfactory injury, or from adipose tissue during starvagrowth rate is to be maintained. Similarly, tion, as well as the production of abnormal zinc supplements added to the diet of children metabolites in disease can provide molecules suffering from acrodermatitis enteropathica able to form stable co-ordination complexes appear to have a dramatic effect, suggesting with zinc. This may remove some zinc from albumin, increase the proportion of low an inherent zinc deficiency disorder. A more common situation in which a molecular weight zinc, present an increased degree of tissue zinc lack is to be expected, filtered load to the renal tubules resulting in is in the severely ill post-operative, or badly an increased zinc clearance. This could be injured patient, particularly if parenteral the mechanism of the zincuria in diverse feeding is required. The total zinc loss from conditions such as diabetes, pancreatitis, all sources such as faeces, urine, G.L tract porphyria, histidinaemia and other clinical fluids, blood, wound exudate and sweat can situations. The LV. infusion of amino acids, be as much as 1 mmol per day. The use of certain drugs and the oral administration of amin c acid infusions can further promote chelating agents like penicillamine, will have

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a similar effect. In severe liver disease there ment of the extent of any negative zinc may be a failure of zinc binding to plasma balance will provide a more logical basis for proteins and in the nephrotic syndrome the deciding the amount of zinc required but direct excretion of zinc bound to albumin can some further study is needed as to the most appropriate form of zinc to use and the best be expected. The extent of zinc loss will determine the routes of administration. clinical significance of such secondary disIt is clear that the full biological significance of zinc in human nutrition is not yet appreciturbances of zinc metabolism. The oral administration of considerable ated and that much fundamental work amounts of zinc (about 2.3 mmoljday) as remains on the very basic role this metal zinc sulphate has been used with some success plays in human health and disease. G. S. FELL in the treatment of varicose ulcers or other poorly healing wounds. This amount is at REFERENCES least 10 times the recommended daily intake Fodor, L., Escbner, J., Dick, W., Abnefield, F. W. (1972). The clinical significance of the zinc deficiency of dietary zinc and it seems probable that syndrome, relationships between zinc deficiency and any clinical effects are pharmacological hypoproteinaemia, Anaesthetist, 21, 456 (in Gerrather than the correction of an inherent or man) acquired tissue deficiency. Some caution J. A., Smith, J. C., Irwin, M. J. (1974). A should be excercised in the prolonged admin- Halsted, conspectus of research on zinc requirements of istration of such a potent stimulus to growth man. Journal of Nutrition, 104, 345 and the possibility of adverse interactions on A. (1972). Complete intravenous nutrition, the gastrointestinal absorption of other trace WretliDcl, theoretical and experimental background. Nutrition metals must be remembered. The measureand Metabolism, 14, Suppl, I, p. 11

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Zinc in clinical nutrition.

Scot. meel. J., 1975, 20: 101 ZINC IN CLINICAL NUTRITION urinary zinc loss so that unless zinc is deliberately added to the dietary regime, some The...
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