Dietary zinc intake and zinc concentrations of plasma, erythrocytes, and breast milk in antepartum and postpartum lactating and nonlactating women: a longitudinal study.

The zinc status of a group of 23 lactating and 13 nonlactating women was assessed longitudinally from 37-wk gestation through 6 months postpartum. Dietary zinc intake was determined by chemical analysis of 3-day duplicate plate food composites. In addition, zinc concentrations were measured in plasma, erythrocytes, and breast milk. The mean dietary zinc intake of both groups of postpartum women as determined by direct analyses was 42% of the Recommended Dietary Allowances or less. The plasma and erythrocyte zinc concentrations were not significantly different between the lactating and nonlactating women. Plasma zinc concentration increased from the time of delivery to one month postpartum for both groups and did not significantly increase further through 6 months postpartum. Erythrocyte zinc decreased from delivery through 6 months postpartum for both groups. Breast milk zinc concentration decreased with the duration of lactation. The calculated zinc intake of infants from breast milk was less than 50% of the Recommended Dietary Allowances. There was no correlation of maternal dietary zinc intake or maternal plasma and erythrocyte zinc with the concentration of zinc in breast milk.