Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/17/2004
Publication Date: 6/4/2004
Citation: Lowe, N.M., Woodhouse, L.R., Sutherland, B., Shames, D., Burri, B.J., Abrams, S.A., Turnlund, J.R., Jackson, M.J., King, J.C. Kinetic parameters and plasma zinc concentration correlate well with net loss and gain of zinc from men. J. Nutr. 134: 2178-2181, 2004. Interpretive Summary: Although 10% of the US population consumes less than 50% of the recommended zinc intake, a sensitive measurement of their zinc status has not been identified. The purpose of this study was to identify when of the various methods used to measure zinc status responded to a net loss or gain of body zinc during acute changes in zinc intake. Five men were fed diets that were virtually free of zinc or that provided the recommended intake (12 mg/d). The men lost an average of 39 mg zinc during the zinc-free diet and gained an average of 108 mg zinc when repleted by feeding the recommended intake. Plasma zinc concentrations best reflected the change in total body zinc. It was followed by endogenous zinc excretion and the total flux of zinc out of the plasma. Thus, plasma zinc is a reliable indicator of loss and gain of whole body zinc when there are acute changes in the diet intake.
Technical Abstract: Background: The search for a reliable, convenient indicator of Zn status has been the focus of research for several decades. Plasma Zn concentration is still the most widely used clinical measurement, despite the known problems of interpretation. More recently, it has been sugggested that isotopically determine kinetic parameters such as the exchangeable ZN pool (EZP), may more accurately reliably reflect body Zn status. Objective: The objective of this study was to examine the relationship between net body Zn loss and gain during acute changes in dietary Zn intake with clinical, biochemical and kinetic indices of Zn status. Design: Five men participated in an 85-day Zn depletion/repletion study conducted in the metabolic ward at the USDA WHNRC. Net body Zn loss and gain was determined from the difference between dietary plus intravenous Zn and Zn excretion. Biochemical indicators of Zn status included plasma Zn concentration (PZn), alkaline phosphatase activity (AP), and retinol binding protein concentration. (RBP). Following oral and intravenous administration of stable isotopes of Zn, a compartmental model was used to detdrmined EZP mass, fractional Zn absorption (FZA), endogenous zinc excretion (EZE) and plasma Zn flux. The change in each of these kinetic and biochemical parameters was compared with net Zn loss/gain by regression analysis. Results: PZn best reflected the changes in total body Zn (r2=0.826), followed by EZE (r2=0.773) and plasma Zn flux (r2-0.766). Conclusions: Under conditions of acute Zn depletion, PZn appears to be a reliable and conventient means of assessing Zn status.