The effect of zinc supplementation on plasma lipids and low-density lipoprotein oxidation in males

Recent studies in animals and in vitro support the hypothesis that zinc, an essential micronutrient, possesses antioxidant properties. The aims of this study were to determine whether zinc provides antioxidant protection in humans by decreasing low-density lipoprotein (LDL) oxidizability and to determine the effect of zinc supplementation on plasma lipid and its distribution among lipoproteins. Ten healthy male volunteers were recruited to participate in a randomized crossover trial. Subjects were asked to consume 50 mg zinc as 220 mg zinc sulphate (equivalent to 4 x recommended dietary intake, or RDI) daily for 4 weeks, followed by placebo, and vice versa. Venous blood samples were collected at 2-week intervals for the determination of plasma lipids and the in vitro oxidizability of LDL in the presence of copper ions. No changes in the oxidizability of LDL or the plasma concentrations of total cholesterol, high-density lipoprotein (HDL) cholesterol and its subfractions, LDL cholesterol, or triacylglycerol were observed following zinc supplementation compared to placebo. Plasma zinc concentrations were increased significantly, indicating that the lack of effect was not due to poor compliance. The antioxidant effect of zinc in relation to LDL was not demonstrated in humans at this dose, and higher doses are unlikely to be effective given the adverse interaction with copper metabolism and the potential decrease in the activity of superoxide dismutase, a free radical quenching enzyme. The findings of this study suggest that zinc provides little, if any, antioxidant protection against LDL oxidation in humans.