Abstract
A sensitive and reliable biomarker of zinc status has yet to be identified, but observational research suggests that the exchangeable zinc pool (EZP) size may be a possible biomarker. This randomized, placebo-controlled trial aimed to compare the change in EZP size from baseline to endline in 174 children who were preventatively supplemented with 10 mg of zinc as part of a multiple micronutrient power (MNP) or as a standalone dispersible tablet for 24 weeks versus a placebo powder. The effects of systemic inflammation on EZP size were also evaluated. Zinc stable isotopes were administered intravenously to children at baseline and endline, and the EZP was measured by the urine extrapolation method. A total of 156 children completed the study with the zinc dispersible tablet group having the greatest increase in EZP (14.1 mg) over 24 weeks when compared with the MNP group (6.8 mg) (p < 0.01) or placebo group (2.0 mg) (p < 0.001). Median EZP size was not different between children with normal or elevated serum inflammatory markers. EZP size was responsive to longitudinal zinc supplementation and reflected the expected difference in bioavailability for two forms of supplementation. The apparent absence of an effect of inflammation on EZP size may offer an advantage for use as a biomarker for group comparisons between different interventions.
Highlights
A sensitive and reliable biomarker of zinc status remains elusive
The primary aim was to compare the change in the exchangeable zinc pool (EZP) size from baseline to endline in a subgroup of children at risk for zinc deficiency who were preventively supplemented with 10 mg of zinc as part of an micronutrient power (MNP) added to a single meal each day, as a standalone daily dispersible tablet, vs. a placebo powder for 24 weeks
Serum zinc concentrations demonstrated a pattern of change that was similar to the changes in EZP for the three groups. These findings indicate that, on average, the size of EZP reflected changes in zinc status associated with a period of supplementation
Summary
Serum or plasma zinc and proxy indicators such as dietary zinc intake and stunting are most commonly used to assess zinc status at the population level, but each have limitations that make evaluation of zinc status challenging [1] Another putative measure of zinc status is the exchangeable zinc pool (EZP), or the size of the combined pools in the body that readily exchange with zinc in the plasma within 2–3 days [2]; the zinc in liver is a major portion of the EZP in children. This rapidly exchanging zinc has been estimated to include approximately 10% of total body zinc and its availability is proposed to be critical for zinc normal metabolism and homeostasis. Unlike serum or plasma zinc, which is a negative acute phase reactant, EZP may be unaffected by systemic inflammation, making it a potentially more robust marker for zinc status [4]
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