The Size of the Exchangeable Zinc Pool (EZP) is Related to Age, Body Size, Gender and Plasma Zinc Concentration in Adults

Abstract

The EZP is the pool of rapidly exchanging, metabolically active zinc (Zn) in the human body. Its size is measured routinely in stable isotope tracer studies of Zn absorption, and it has been given consideration as a potential biomarker of Zn status. Linear regression models were used to investigate relationships of EZP to body size, age, gender, plasma Zn concentration, dietary Zn intake and absorbed Zn in data from studies of healthy adults. EZP size measurements ranged from 75 to 280 mg in subjects between 18 and 83 yrs of age. Age, body weight (or surface area), gender and plasma Zn (in decreasing order of importance) were all significant predictors of EZP in multiple regression models of data from 100 subjects having adequate Zn intake (>7 mg/d) and absorption (> 2.8 mg/d). The models showed EZP size to increase with body weight and plasma Zn, and to decrease with age. The gender difference was largest in young adults (EZP in males was 50 mg larger at 20 yrs of age) and decreased to equality at 80 yrs. Younger subjects with Zn intakes-absorption lower than the ranges mentioned above had smaller EZP sizes on average than model predictions when controlling for age, body weight and gender. No such difference was evident in elderly subjects having lower intakes-absorption. EZP sizes in subjects experiencing severe Zn depletion were consistently lower than the model's 95% prediction intervals. The models have descriptive and predictive utility: contributing to an understanding of the physiological characteristics of the EZP, establishing normal values and ranges for healthy subjects and evaluating the suitability of EZP size as a biomarker of Zn status.