Bioavailability in Man of Iron in Human Milk and Cow's Milk in Relation to Their Calcium Contents

Abstract

ABSTRACT: Iran absorption from human milk and cow's milk was compared in the same subjects using two radio-iron tracers and extrinsic labeling of the iron. Previously observed higher iron absorption from human milk was confirmed as 19.5 ± 17.3% (mean ± SD) in cow's milk vernus 48.0 ± 255% in human milk; mean individual absorption ratio was 039 ± 0.18 (p < 0.0001). Cow's milk has a several times higher content of calcium, recently established to be a potent inhibitor of iron absorption. Adding cakhim chloride to human milk in amounts to equate the calcium content of cow's milk significantly reduced bon absorption (39.1 ± 17.8% (mean ± SD) versus 213 ± 10.6%); men individual absorption ratio with or without added calcium was 038 ± 0.12 (mean ± SD) (p < 0.0001). Differences in calcium content could explain at least 70% of the difference in iron bioavailability between milks. It is suggested that the remaining 30% difference may mainly be an artifact related to inhomogeneous ra-dioiron-labeling of milk iron compounds, especially in human milk, and that the main difference in true iron absorption between human and cow's milk is related to then-different calcium contents. The rather high fractional iron absorption from human milk can be explained by its tow iron content There is nothing to indicate that human milk contains any enhancer of iron absorption. The marked inhibiting effect of cakinm on iron absorption should be considered fa the design of infant formulas to achieve an optimal balance in the contents of cakinm and iron.