Bioavailability of caseinophosphopeptide-bound iron.

Iron deficiency, one of the main worldwide nutritional deficiencies, results from the low bioavailability of most dietary iron, including cow milk. Hydrolysis of the cow milk protein casein produces low molecular weight caseinophosphopeptides (CPPs). Binding of iron to CPPs keeps it soluble in the digestive tract and prevents the formation of high molecular weight ferric hydroxides, which are poorly absorbed. Previous experimental studies have shown that iron bound to the phosphopeptide containing the first 25 amino acids of beta-casein, or beta-CN (1-25), is well absorbed and corrects efficiently iron deficiency. We sought to assess in vivo iron absorption and uptake by tissues involved in iron metabolism and storage (liver, spleen, bone marrow), using radiolabeled iron. beta-CN (1-25)-Fe displayed better absorption and tissue uptake by the vascularized rat loop model compared with a control substance, ferric ascorbate. The metabolism of beta-CN (1-25)-Fe labeled with iron 59, added to cow milk, was also studied in young women. Although the absorption of beta-CN (1-25)-Fe was not significantly higher than that of ferrous sulfate, it displayed significantly higher tissue uptake. This increase was transient and had disappeared by the 14th day of the study, suggesting that iron was used for metabolic purposes.