Zinc nutritional status during pregnancy: a longitudinal study

Abstract

Dietary zinc (Zn) intake and selected biochemical indices of Zn status were studied longitudinally at monthly intervals in 46 pregnant middle-income women, 10 of whom received a daily supplement of 15 mg Zn. Mean dietary Zn intake for the nonsupplemented subjects (group A) was 11.3 +/- 4.1 mg/day (56% of the Recommended Dietary Allowances), and for the Zn-supplemented subjects (group B) was 21.7 mg/day (109% of the Recommended Dietary Allowance), including an average intake of 11.1 mg/day as supplemental Zn. The mean plasma Zn concentration of group A at 2 months gestation, 71.4 +/- 9.8 micrograms/dl, was 17% lower than that of nonpregnant control women, and continued to decline significantly (p less than 0.01) between 2 and 10 months gestation. Plasma Zn of group B did not differ significantly from group A at any stage of gestation. Mean serum alkaline phosphatase activity of group B was higher than that of group A at 7 of 8 months studied (p less than 0.05). The level of prenatal iron supplementation in group A was negatively correlated with alkaline phosphatase activity and plasma Zn in the 2nd and 3rd trimesters, respectively. It is concluded that an early and progressive decline in plasma Zn which is not influenced by Zn intake occurs during gestation. Tentative standards for lower limits of normal at monthly intervals have been suggested. The higher alkaline phosphatase activity of group B compared with group A suggested that the dietary Zn intake of the latter was suboptimal. Prenatal supplemental iron may adversely affect maternal Zn status.