Effect of iron fortification of infant formula on trace mineral absorption

This study was designed to examine whether iron fortification of infant formulas has an effect on utilization of other nutrients, particularly the trace elements zinc and copper. Metabolic balance studies were performed with seven normal infants who were between 43 and 420 days of age. Two formulas of nearly identical composition except for iron concentration (10.2 and 2.5 mg/L) were fed. Each infant had four balance studies performed, two while being fed formula 10.2 and two while being fed formula 2.5, in an alternating sequence. No effect of formula iron concentration was evident on absorption and/or retention of nitrogen, fat, calcium, and magnesium. Although absorption of phosphorus was significantly (p less than 0.05) less with formula 10.2 than formula 2.5, the difference was trivial. No effect on absorption of zinc was seen. However, absorption of copper was only 13.4% (SD 13.0) of intake when formula 10.2 was fed, compared with 27.5% (SD 15.3) of intake when formula 2.5 was fed. The difference was statistically significant (p less than 0.01). We conclude that iron in amounts present in iron-fortified formulas has a measurable effect on copper utilization. Because the magnitude of the effect is relatively small, we doubt that the finding is clinically relevant.