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

The concentration and bioavailability of zinc was analyzed in 10 varieties of milk. The concentration of zinc averaged 4.1 microgram/ml in unprocessed (raw) cow's milk; fortified infant formulas contained about 3 to 5 microgram Zn/ml; human breast milk and processed cow's milk contained approximately 2 microgram Zn/ml; sweetened condensed milk contained 1.3 microgram Zn/ml, and reconstituted nonfat dry milk contained 0.4 microgram 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.