ABSORPTION OF CALCIUM, ZINC, AND IRON FROM BREAST-MILK BY 5-MONTH-OLDTO 7-MONTH-OLD INFANTS

Data are scarce regarding mineral bioavailability from human milk in o lder infants who may also be receiving solid foods (beikust), We measu red the absorption of Ca, Zn, and Fe in 14 healthy, nonanemic 5-7-mo-o ld breast-fed infants whose mothers' milk was extrinsically labeled wi th stable isotopes (Ca-44, Zn-70, and Fe-58) of these minerals. In add ition, Ca and Zn stable isotopes (Ca-46 and Zn-67) were administered i .v., and a second isotope of Fe (Fe-57) was given orally without food as a non-meal dose. Subjects were not receiving any artificial infant formula or cow's milk, but most (10/14) were receiving beikost. Ca and Zn absorption was calculated using the urinary excretion of the isoto pes during the 24 h after dosing (Ca) or their urinary ratio 72 h afte r dosing (Zn). Fe absorption was calculated using the red blood cell i ncorporation at 14 d. Fe absorption averaged 20.7 +/- 14.8% from the F e-58 given with human milk (geometric mean, 14.8%) and 17.7 +/- 15.1% (geometric mean, 11.0%) from the Fe-57 non-meal dose. Ca absorption av eraged 61.3 +/- 22.7% and Zn absorption (n = 10) averaged 49.5 +/- 18. 5%. Absorption of Fe (natural logarithm) from the non-meal Fe dose (Fe -57) but not from the human milk (Fe-58) was significantly negatively correlated to serum ferritin (r = -0.70, p = 0.007 versus r = -0.35, p = 0.24). At the intake levels in this study, total daily Fe, Ca, and Zn intakes from beikost were not significantly correlated to their fra ctional absorption from breast milk, but Fe intake from beikost was si gnificantly negatively correlated to absorption of Fe from the non-mea l dose (r = -0.61, p = 0.021), We conclude that minerals are well abso rbed from human milk in older infants after the introduction of beikos t to the diet.