Objective: To evaluate the effects of usual dietary intake of zinc and of zinc supplementation during pregnancy on plasma and erythrocyte zinc concentrations.
Design: A randomized, double-blind, placebo-controlled trial.
Subjects: Low-income African-American women (n = 580) assigned randomly to groups at 19 weeks of gestation.
Intervention: A daily dose of zinc (25 mg) or a placebo until delivery.
Main outcome measures: Plasma, erythrocyte, and dietary zinc levels.
Statistical analyses: Multiple regression and repeated measures analysis of variance.
Results: In both the placebo and the supplemented groups, when all subjects were grouped by usual dietary zinc intake above or below the median (12 mg/day), results were the same: Women with high dietary zinc intake had higher erythrocyte zinc levels at the time of randomization and at all subsequent measurements during pregnancy than those who had low dietary zinc intake (P < or = .06; difference not significant for zinc-supplemented group); no difference was observed for plasma zinc levels. On the other hand, when the subjects were stratified at the median by total daily zinc intake (usual dietary zinc + 25 mg zinc supplement) during pregnancy, a significant difference in plasma zinc levels (P < .005) was found between women with high total zinc intake (mean = 38 mg/day) and low total intake (mean = 13 mg/day) at 26, 32, and 38 weeks of gestation; however, no such differences were found in erythrocyte zinc levels.
Applications: These results should help dietitians and other health professionals better understand the expected changes in plasma and erythrocyte zinc levels during pregnancy, and the relationship between dietary and supplemental zinc and zinc nutriture.