Effect of zinc supplementation on protein metabolism in late–middle-aged men: The Zenith study

Abstract Objective Zinc (Zn) is an essential trace element that is a potent enhancer of protein metabolism due to its numerous roles in metabolic processes. Protein turnover decreases with age. We determined whether a Zn supplementation, which increases serum Zn concentration and Zn exchangeable pool mass, modifies whole-body protein turnover and albumin and fibrinogen synthesis rates in late–middle-aged men. Methods Three groups of 16 healthy subjects 55–70 y of age participated in a randomized, doubled-blinded, placebo-controlled intervention. Each group received 0, 15, or 30 mg/d of supplemental Zn for 6 mo. At the end of the supplementation period, each subject received an intravenous infusion of L-[1- 13 C] leucine to quantify whole-body leucine fluxes and synthesis rates of albumin and fibrinogen. Results In the placebo group, mean ± SEM whole-body leucine fluxes to protein synthesis, to oxidation, and from protein degradation were 1.46 ± 0.05, 0.40 ± 0.01, and 1.73 ± 0.06 μmol · kg −1  · min −1 , respectively. Zn supplementation did not significantly change whole-body leucine fluxes. In the placebo group, plasma concentration and fractional rate of protein synthesis were 45 ± 1 g/L and 8.2 ± 0.6%/d for albumin and 3.6 ± 0.2 g/L and 16.7 ± 1.3%/d for fibrinogen, respectively. Zn supplementation did not significantly change these parameters or the absolute rates of synthesis of these proteins. Conclusion Increasing Zn supply does not modify whole-body protein metabolism and synthesis rates of albumin and fibrinogen in late–middle-aged men.