Erythrocyte Incorporation of Iron Is Similar in Infants Fed Formulas Fortified with 12 mg/L or 8 mg/L of Iron ,

Abstract

Although feeding of formulas with iron concentration of 215 μmol/L (12 mg/L) is a reliable means of preventing iron deficiency, high intakes of iron may adversely affect absorption of copper and zinc. Because data are not available to establish whether fortification at a lower level would result in equivalent iron absorption, we tested the hypothesis that iron absorption is greater by infants fed formulas with an iron concentration of 215 μmol/L (12 mg/L) than by those fed formulas with an iron concentration of 143 μmol/L (8 mg/L). Fifty-two normal infants entered the study at 112 ± 4 d of age, and 46 of these were successfully studied until 196 d of age. Using the stable isotope 58Fe, we determined erythrocyte incorporation of iron by infants fed Formula 8 [iron approximately 143 μmol/L (8 mg/L)] and by infants fed Similac with Iron® [iron approximately 215 μmol/L (12 mg/L)]. On each of three test days beginning at 154 d of age, a major portion of the formula was labeled with 58Fe. Geometric mean erythrocyte incorporation of iron adjusted for plasma ferritin concentration at 168 d of age was 4.82 μmol/d (0.269 mg/d) by infants fed Formula 8 and 5.21 μmol/d (0.291 mg/d) by infants fed Similac with Iron. Corresponding values at 196 d of age were 5.12 and 5.41 μmol/d (0.286 and 0.302 mg/d). The differences in quantity of iron incorporated into erythrocytes by infants fed Formula 8 and Similac with Iron were not statistically significant (P = 0.66 at 168 d of age, P = 0.75 at 196 d of age) and were judged to be nutritionally trivial. Because we were unable to provide support for our hypothesis that iron absorption is greater by infants fed formulas providing 215 μmol (12 mg) of iron per liter than by those fed formulas providing 143 μmol (8 mg) of iron per liter, we conclude that, pending the results of further studies, it is reasonable to decrease the iron concentration of iron-fortified infant formulas.