Letter: Effect of food on zinc absorption

A standardized oral zinc tolerance test for assessment of zinc absorption in dogs

Three oral zinc tolerance tests using increasing doses of elemental zinc (0.5, 0.75 and 1.0 mg/kg) given as zinc sulphate (ZnSO4.7H2O) were carried out in eight normal beagles. The zinc tolerance curves obtained were similar to those described in man, with the peak plasma zinc concentration occurring 2 h after dosing. There was a considerable variation between individual animals in the peak plasma zinc concentration achieved with each dose. This would appear to limit the value of a zinc tolerance test in assessing the efficiency of zinc absorption in individuals, although it may be of value in making comparisons between groups of dogs.

Pharmacokinetic study of orally administered zinc in humans: evidence for an enteral recirculation

Starting from the experimental design of the established 'Zinc Tolerance Tests', the absorption and distribution of the essential trace element zinc in humans was investigated in 10 subjects by performing a pharmacokinetic study of the serum zinc profile after oral administration of a pharmacological dose of the metal, i.e. 0.69 mmol (45 mg) zinc as ZnSO4.7 H2O. The adopted experimental conditions include frequent measurements of serum concentrations, a total investigation time of 8 h after ingestion, and a correction of basal zinc levels taking into account the circadian variation. Rebound effects were evidenced in the time versus concentration curves showing a regular recycling of the element in the digestive tract. Estimation of the parameters by an original method allowed us to calculate the characteristics of the cycles. The first one occurred after 1.4 h, before the time needed for appearance of the maximum concentration which was around 2.3 h, and exhibited mean reabsorption of 70% of administered dose. The subsequent ones, maximum 5 during the investigation period, appeared at regular intervals of approximately 1.2 h, with a decrease in the quantity reabsorbed. These observations are consistent with the previously reported endogenous secretion of zinc, a physiological mechanism contributing to zinc homeostasis.

Zinc, copper, and parenteral nutrition in cancer. A review

Literature concerning zinc and/or copper investigations pertaining to cancer is surveyed; the interrelationships of zinc, copper, and parenteral nutrition (PN) in cancer are examined; and the advantages of adequate nutritional support for patients with malignancies are discussed. Zinc and copper are both essential trace elements and, therefore, are necessary nutrients for cancer patients. Zinc supports growth, including that of neoplasia; copper is a zinc competitor and antagonist; and cancer patients on PN are in danger of becoming both zinc- and copper-deficient. The addition of these trace elements as supplements to PN formulae is undertaken with knowledge of only the approximate concentrations of zinc and copper in total intake, but without knowledge of specific requirements for cancer patients for these trace elements, of all the possible interactions of zinc and copper with each other or different trace elements, or even of zinc and copper lower levels of toxicity in cancer patients; balance studies are needed to determine zinc and copper requirements in them. In the future, it is conceivable that manipulations of the host nutrients might be used to control tumors. This might be accomplished by adjusting total PN formulae so that required nutrients will be presented to a cancer patient in such amounts and in such ratios that a desired alteration may be effected in that patient's metabolism.

Influence of zinc-ligand mixtures on serum zinc levels in rats

The influence of various salts, chelates, and other complexes of zinc given by gavage on serum zinc levels in rats was studied. Serum zinc concentrations were determined over 6 hr after administration of zinc sulfate at doses of 5, 10, 20, 50, and 100 mg of zinc/kg. Serum zinc levels following doses of zinc salts and complexes were compared with those after zinc sulfate. Phytic acid, aminopolycarboxylic acids (including edetate disodium), and penicillamine significantly suppressed increases in serum zinc concentration. Some natural amino acid-zinc sulfate mixtures (those with lysine, cysteine, glycine, and histidine) produced greater levels than the equivalent dose of zinc sulfate alone. Several thiocarboxylic acids, such as mercaptoacetic acid and thiosalicylic acid, also increased serum zinc concentrations. These observations form a basis for attempted modification of zinc absorption in other species.