Objectives : The effect of infection and inflammation on EZP size, a putative biomarker of Zn status, is unknown. We sought to evaluate the relationship of EZP to systemic inflammation in a group of toddlers with high risk of Zn deficiency and EED.
Methods : Subjects were 112 children from an urban slum area in Dhaka, Bangladesh, aged 18-24 months, at risk of EED and who participated in stable isotope studies of Zn homeostasis while on habitual diets. All children underwent screening for EED, using L:M ratio, and multiple markers of systemic and intestinal inflammation were obtained. EZP size was measured from intravenously administered stable isotope of Zn, with urine collections obtained over 4 days, starting 3 days after isotope administration. The size of EZP was calculated by dividing the mass (mg) of intravenous isotope dose (67Zn or 68Zn) by the enrichment value at the y intercept of the linear regression: EZP (mg) = IV dose/y-intercept. The intercept is estimated from linear regression of a semi-log plot of urine enrichment data. Multiple regression analysis was applied to examine relationships among child size, serum Zn, markers of systemic and intestinal inflammation and EZP. EZP was also compared to previously published evaluation of EZP from multiple studies (Miller LV, J Nutr, 2016).
Results : Mean (± SD) age of subjects was 19 ± 2 months; mean weight 9.1 ± 1.0 kg; mean dietary Zn was 2.7 mg/d. Mean EZP was 3.7 ± 0.5 mg/kg, compared to an expected value of 4.1 mg/kg based on the previous published analysis of all child data; all data points were within the 90% prediction interval from those data (Figure). Compared to existing child data, these children weighed less and had smaller EZP. EZP/kg was directly associated with serum Zn concentration, and inversely associated with hemoglobin and dietary Zn (best model R2 = 0.24). The analyses indicated no evidence of an association of EZP/kg with any biomarkers of inflammation.
Conclusions : The apparent absence of an effect of inflammation on EZP size may provide some advantage over serum Zn. The inverse relationship with dietary Zn suggests redistribution of Zn pools in chronic marginal Zn status. Evaluation of utility of EZP as a biomarker of Zn status will require measurement during controlled interventions.
Funding Sources : Bill & Melinda Gates Foundation