Iron absorption and milk
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Iron Absorption from Human Milk vs. Cow’s Milk and Infant Formulas
Research consistently shows that iron is absorbed much more efficiently from human (breast) milk than from cow’s milk or most infant formulas. Studies have found that infants absorb about 49–70% of the iron in breast milk, compared to only about 10–30% from cow’s milk and iron-supplemented formulas, even though breast milk contains much less total iron than these alternatives 129. This high bioavailability means that breastfed infants generally have better iron stores in early infancy and are less likely to develop iron deficiency, especially if solid foods are introduced later 29.
Factors Affecting Iron Absorption in Milk
Milk Protein Composition and Iron Bioavailability
The proteins in cow’s milk, especially casein and whey, can significantly reduce iron absorption. These proteins bind iron tightly, making it less available for absorption in the gut. When casein and whey are hydrolyzed (broken down), iron becomes more available, but the effect is still less than that seen with egg white proteins or human milk . Differences in the structure of casein-derived peptides also affect iron absorption, with some forms (like β-casein phosphopeptides) enhancing absorption more than others . Human milk lacks certain caseins found in cow’s milk, which may partly explain its superior iron bioavailability .
Role of Milk Components Like Lactoferrin and Osteopontin
While human milk contains lactoferrin, a protein thought to help with iron absorption, studies show that simply adding lactoferrin to formula does not replicate the high absorption rates seen with breast milk . Recent research also highlights osteopontin, another milk protein, which can bind iron and help its uptake in intestinal cells—even in the presence of inhibitors like phytic acid—suggesting a potential role in improving iron delivery from milk .
Influence of Other Milk Additives
Adding ascorbic acid (vitamin C) to cow’s milk formulas significantly increases iron absorption, sometimes doubling it, while the amount of milk fat, added carbohydrates, or acidification of the milk does not have a notable effect . This suggests that vitamin C is a key enhancer of iron absorption in fortified milks.
Iron Fortification and Supplementation Strategies
Iron-fortified formulas use different iron salts, and their bioavailability varies. For example, iron from ferrous ammonium phosphate and ferrous sulfate is absorbed much better than from ferric pyrophosphate when added to milk . However, even with fortification, the percentage of iron absorbed from formula is still lower than from breast milk 12.
When iron supplements are given to young children, absorption is higher if the supplement is taken with juice (which often contains vitamin C) rather than with cow’s milk, again highlighting the inhibitory effect of cow’s milk on iron absorption .
Conclusion
Human milk provides iron in a highly bioavailable form, allowing infants to absorb much more of the iron it contains compared to cow’s milk or most formulas, despite its lower iron content. The superior absorption from human milk is not solely due to its overall composition or the presence of specific proteins like lactoferrin, but likely results from a combination of factors, including the absence of certain inhibitory proteins and the presence of unique enhancers. Cow’s milk proteins, especially casein and whey, inhibit iron absorption, but this can be partially overcome by hydrolyzing the proteins or adding vitamin C. For infants who are not breastfed, iron-fortified formulas with added vitamin C and careful choice of iron compounds can help improve iron status, but breast milk remains the gold standard for iron bioavailability in early infancy 12356789+1 MORE.
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