Maternal zinc intakes and homeostatic adjustments during pregnancy and lactation

Abstract

Zinc plays critical roles during embryogenesis, fetal growth, and milk secretion, which increase the zinc need for pregnancy and lactation. Increased needs can be met by increasing the dietary zinc intake, along with making homeostatic adjustments in zinc utilization. Potential homeostatic adjustments include changes in circulating zinc, increased zinc absorption, decreased zinc losses, and changes in whole body zinc kinetics. Although severe zinc deficiency during pregnancy has devastating effects, systematic reviews and meta-analysis of the effect of maternal zinc supplementation on pregnancy outcomes have consistently shown a limited benefit. We hypothesize, therefore, that zinc homeostatic adjustments during pregnancy and lactation improve zinc utilization sufficiently to provide the increased zinc needs in these stages and, therefore, mitigate immediate detrimental effects due to a low zinc intake. The specific questions addressed are the following: How is zinc utilization altered during pregnancy and lactation? Are those homeostatic adjustments influenced by maternal zinc status, dietary zinc, or zinc supplementation? These questions are addressed by critically reviewing results from published human studies on zinc homeostasis during pregnancy and lactation carried out in different populations worldwide.

Keywords: diet; homeostasis; lactation; pregnancy; zinc.

Figure 1

Maternal and cord blood erythrocyte (RBC), and placental metallothionein (MT) at delivery, in Peruvian and Brazilian women. Peruvian women (□): n = 158 (maternal erythrocytes) and n = 30 (placenta and cord blood erythrocytes) [33]. Brazilian women (■): n = 40 (erythrocytes and placenta) [38]. Comparison of each variable between groups was done by t-test. All comparisons were significant (p < 0.05).

Figure 2

Percent zinc absorption during pregnancy and lactation in Californian and Brazilian women. Californian women (□), n = 13 [30]. Brazilian women (■), n = 8 [31]. Means within each group with different superscript letters are significantly different by repeated measures ANOVA and Tukey’s range test, p < 0.05.