Iron absorption and iron gains from birth to 6 months in breastfed and formula fed infants

Many infants develop iron deficiency by 6 months of age. Yet little is known about iron absorption or iron gains in early infancy. We used a novel isotope dilution method to measure dietary iron absorption from birth to 6 months in healthy term infants who were fully breastfed (BF), fully formula-fed (FF) or received mixed feeding (MF). In this prospective observational study, we administered stable iron isotopes (57Fe, 58Fe) to pregnant women and used maternal-fetal iron transfer to uniformly label the newborn. Dilution of enriched infant body iron by dietary iron with natural isotopic composition was used to quantify iron absorption from birth to 6 months and calculate iron bioavailability and iron gains. In BF infants (n=8), FF infants (all receiving high-iron formula) (n=7) and MF infants (n=8), median (IQR) iron absorbed was 0.128 (0.095–0.180), 0.457 (0.374–0.617) and 0.391 (0.283–0.473) mg/day (BF vs FF, p<0.01); dietary iron bioavailability was 42.3 (20.4–52.7), 3.2 (2.5–7.4) and 7.3 (6.4–11.3)% (BF vs FF, p=0.001; BF vs MF, p<0.05); and total iron gains were 0.027 (-0.002–0.055), 0.349 (0.260–0.498) and 0.276 (0.175–0.368) mg/day (BF vs FF, p<0.001; BF vs MF, p<0.05). In BF infants, iron absorbed just covered basal iron losses, but resulted in minimal iron gains; as a result, hemoglobin, total body iron and circulating iron were lower than in FF infants at 6 months (for all, p<0.01). Most infants (20 of 23) absorbed much less iron then the recommended 0.7 mg/day for 6-month-olds.