Zinc bioavailability and homeostasis

Abstract

Zinc has earned recognition recently as a micronutrient of outstanding and diverse biological, clinical, and global public health importance. Regulation of absorption by zinc transporters in the enterocyte, together with saturation kinetics of the absorption process into and across the enterocyte, are the principal means by which whole-body zinc homeostasis is maintained. Several physiologic factors, most notably the quantity of zinc ingested, determine the quantity of zinc absorbed and the efficiency of absorption. Other factors are age and the time over which zinc is ingested. Zinc from supplements has not been shown to be absorbed differently from that taken with meals that lack inhibitors of zinc absorption. The principal dietary factor known to impair zinc bioavailability is inositol hexa-(and penta-) phosphate or phytate. Modeling of zinc absorption as a function of dietary zinc and phytate accounts for .80% of the variability in the quantity of zinc absorbed. Fitting the model to new data has resulted in continual improvement in parameter estimates, which currently indicate a maximal absorption in adults of '6 mg Zn/d and that the average estimated dietary requirement doubles with 1000 mg dietary phytate/d. Intestinal excretion of endogenous zinc is regulated in response to recent absorption and to zinc status. The quantitative relation of intestinal excretion of endogenous zinc to zinc absorption is currently considered to be of major importance in the determination of zinc requirements. The effects of phytate on intestinal losses of endogenous zinc merit further investigation but are probably not of the same magnitude as its inhibitory effects on absorption of exogenous zinc.Am J Clin Nutr 2010;91(suppl): 1478S-83S.

Scientific Opinion on Dietary Reference Values for zinc

“…The fraction of absorbed zinc then decreases progressively with increasing dietary zinc . The uptake of zinc and its transfer into the body by the enterocyte is regulated in response to the quantity of bioavailable zinc ingested (Chung et al, 2008); this relationship between the quantity of zinc absorbed and that ingested is best fit with saturation response modelling (Hambidge et al, 2010).…”

“…Although experimental data are still limited (Hambidge et al, 2010), there are also theoretical reasons for supporting the conclusion that the relationship between TAZ and total dietary zinc (TDZ) is most appropriately fitted with saturation response modelling. Therefore, the intercept of the TAZ necessary to meet physiological requirements with the saturation response model (Morgan et al, 1975) for the population studied should give the AR for that population.…”

“…The dietary zinc intake required to meet the AR associated with different body weights (as predicted by the model described in Section 5.1.1.5) can be derived from the intersection of the respective physiological zinc requirements (identified on the axes of the absorbed zinc) with the saturation response model curve back-predicting the dietary zinc intake conditional to an expected level of phytate intake. This is illustrated in Figure 2, derived from the established model of phytate effect (Miller et al, 2007;Hambidge et al, 2010). The curves show the relationships of absorbed zinc to dietary zinc for dietary phytate levels of 0 and 900 mg/day, as predicted by the saturation response model.…”

“…These are the data used in the development and early application of the model (Miller et al, 2007;Hambidge et al, 2010). The eligibility criteria were the following: studies of healthy adults, whole-day isotope studies of true zinc absorption, reporting measurements of TDZ, and total dietary phytate (TDP) and TAZ.…”

Linking Agriculture with Health through Genetic and Agronomic Biofortification

“…The efficiency of micronutrients absorption from a diet depends upon the amounts consumed (decreases with an increase in amounts consumed) and the presence of dietary phytate [25] [26]. Phytate forms insoluble complexes, for instance with Zn, that cannot be digested or absorbed because of the absence of intestinal phytate enzymes in humans [27].…”