The effects of a dietary zinc supplement during lactation on longitudinal changes in maternal zinc status and milk zinc concentrations.

Dietary zinc intakes, selected biochemical indices of zinc status, and milk zinc concentrations were determined at monthly intervals throughout lactation for 53 middle-income lactating women, 14 of whom received a daily supplement of 15 mg zinc. Overall mean dietary zinc intake for the non-supplemented group (NZS) was 10.7 +/- 4.1 mg/day (mean +/- SD). The mean dietary zinc intake of the zinc supplemented group (ZS) was 12.2 +/- 3.5 mg/day, with an additional 12.8 +/- 1.5 mg/day from the supplement. For the NZS group, the highest mean plasma zinc concentration of 79 +/- 10 mu/dl, which occurred at month 4, was significantly less than the mean for non-lactating control women (86 +/- 10 micrograms/dl). ZS plasma zinc levels had a pattern similar to that of the NZS group for months 1-7. The rate of decline in milk zinc during lactation was significantly less for the ZS group compared to that of the NZS group (p = 0.02). It is concluded that milk zinc concentrations are influenced by maternal zinc intake within a physiological range and that the effects of low maternal intakes are most apparent with prolonged lactation.