Erythrocyte incorporation of iron by infants: iron bioavailability from a low-iron infant formula and an evaluation of the usefulness of correcting erythrocyte incorporation values, using a reference dose or plasma ferritin concentrations

Bioavailability of iron (Fe) from a low-Fe infant formula was determined by erythrocyte incorporation of Fe-58 14 d after administration in ten health y, non-Fe-deficient infants. Two feeding protocols were compared, with each infant acting as his/her own control. At 140 and 154 d of age, infants wer e fed 1000 g of Fe-58-labelled formula (1.44 mg total Fe/1000 g) as six fee ds over 24 h (Protocol A) or as two feeds/day on three consecutive days (Pr otocol B). A water solution with Fe-57 and ascorbic acid was given separate ly as a reference dose in both study protocols. Erythrocyte incorporation o f Fe-58 and Fe-57 was determined by thermal ionisation mass spectrometry. G eometric mean Fe-58 incorporation was 7.6% (range 3.3-13.5%) with Protocol A as compared to 10.6% (range 6.7-18.6%) with Protocol B (P = 0.05); paired t test. Inter-individual variability of Fe-58 was not reduced by correctin g for the incorporation of Fe-57 from the reference dose, or by correcting for plasma ferritin concentration. Fractional erythrocyte incorporation of Fe from low-Fe infant formula was in the same range as our earlier publishe d data on erythrocyte incorporation of Fe from human milk extrinsically lab elled with Fe-58 (Davidsson ci al. 1994a). The methodological evaluations i ncluded in this study clearly indicate the importance of using standardised study protocols when evaluating Fe bioavailability in infants. Corrections of erythrocyte incorporation data based on plasma ferritin or erythrocyte incorporation of Fe from a reference dose were not found to be useful.