Relative zinc availability in human breast milk, infant formulas, and cow’s milk

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Abstract
The concentration and bioavailability of zinc was analyzed in 10 varieties of milk. The concentration of zinc averaged 4.1 µg/ml in unprocessed (raw) cow's milk; fortified infant formulas contained about 3 to 5 µg Zn/ml; human breast milk and processed cow's milk contained approximately 2 µg Zn/ml; sweetened condensed milk contained 1.3 µg Zn/ml, and reconstituted nonfat dry milk contained 0.4 µg Zn/ml. The mean values for zinc bioavailability to rats were as follows: sweetened condensed milk = 66%; human breast milk = 59.2%; processed cow's milk = 43.7 to 50.9%; unprocessed (raw) cow's milk = 42%; nonfat dry milk = 41.2%; and infant formulas = 26.8 to 39.5%. Assuming similar absorption of zinc in rats and humans, our experimental results provide some guidelines for estimating the quantity of zinc that would actually be absorbed from various types of milk.