Iron absorption from breast milk, cow's milk, and iron-supplemented formula: an opportunistic use of changes in total body iron determined by hemoglobin, ferritin, and body weight in 132 infants.

Abstract

Summary: Iron absorption was measured by using changes in the calculated total body iron (TBI) in infants on three different milk regimens: breast milk (n = 86), home-prepared cow's milk formula (n = 15), and proprietary iron-supplemented infant formula (n = 31) during the first 4 months of life. The TBI was determined as the sum of the hemoglobin iron (HbI) and the body storage iron (BSI). In the latter assessment, we found a close to linear correlation between the concentration of serum ferritin (SF) expressed as the logarithm and the BSI expressed as milligrams per unit of body weight. Accordingly, the BSI could be calculated from SF and body weight. Iron absorption from milk was estimated from the increment of TBI and from the estimated iron intake at different time intervals. From 2-4 months of age the monthly increment of TBI was 33.5 mg in the iron-supplemented formula group, 20 mg in the breast milk group, and 6.5 mg in the cow's milk group. The differences were statistically highly significant (P < 0.001). The calculated percentage intake was about 70% for breast milk iron, about 30% for cow's milk iron, and about 10% for the supplemental iron in infant formula. Our data emphasize the exceptionally high bioavailability of breast milk iron which markedly dropped after the introduction of solid foods at 4 months of age. These data suggest an inhibitory effect of the solid vegetable foods on iron absorption, especially from breast milk. Our findings indicate that exclusive breast feeding is an effective means in preventing iron deficiency in early infancy as an alternative to the use of iron-supplemented infant formulas. Speculation: Quantitative estimation of body iron stores by serum ferritin and body weight provides a way to calculate the amount of total body iron. This method provides a new way to study iron absorption without the use of radioactive isotopes, and indicates unusually high bioavailability of breast milk iron if the solid foods are introduced late.