Changes in zinc and copper concentrations in breast milk and blood of Japanese women during lactation.

To evaluate the changes in zinc and copper concentrations in breast milk and maternal blood during lactation, milk and blood samples were obtained from 80 lactating women during the period between 2 and 201 days of lactation. Zinc and copper concentrations were measured by atomic absorption spectrophotometry. Breast milk zinc and copper concentrations markedly decreased during the first few weeks of lactation and gradually declined for the remaining period. Mean values of milk zinc and copper levels were 1.76 and 0.29 micrograms/ml, respectively, between 15 and 84 days after parturition and were 0.76 and 0.19 microgram/ml between 85 and 201 days of lactation. Calculated daily intakes of these minerals for infants from breast milk were markedly lower than those of US Recommended Dietary Allowances. Plasma zinc levels of lactating mothers increased as lactation progressed, whereas erythrocyte zinc and plasma copper concentrations decreased. Plasma zinc and copper and erythrocyte zinc values returned to normal approximately three months after parturition.