Effects of Dietary Zinc Supplement during Lactation on Longitudinal Changes in Plasma and Milk Zinc Concentrations

Effects of dietary zinc supplement during lactation on maternal plasma zinc and milk zinc concentrations through 5 months of lactation were examined. One hundred and thirty eight healthy lactating mothers received a weekly 100 mg elemental zinc supplement (ZG, n = 67) or placebo (PG, n = 71) starting one week postpartum in a double blind, randomized design. Milk and plasma zinc concentrations were determined by atomic absorption spectrophotometer.
During the course of study, there was not a significant difference between ZG and PG groups in dietary zinc and energy intake. The mean plasma zinc concentration during the 1st week and 5th month were 134±49.1 and 115.6±23g/dl (p=0.005) for PG group, respectively: that of the ZG group these figures were 124.9±52.8 and 121±27.1g/dl (p=0.38), respectively. The mean serum alkaline phosphatase concentration of the 1st week and 5th month were 94.8±37 and 92.6±29.9 iu/l for PG group, respectively: that of the ZG group these figures were 90.5±36 and 90±29 iu/l (p=0.21), respectively. Milk zinc concentration declined significantly over the course of study for two groups, with the sharpest decline occurring during the first 2 months. The mean monthly zinc concentration of ZG group declined from 310±138 during the 1st week to 118±64g/dl at 5th month (declined by 52%). Corresponding means for PG group were 322±161 and 109±70g/dl (declined by 60%), respectively. Milk zinc concentration was significantly different between two groups for 3 and 4 months. A similar study, however, with different zinc dose and administration manner, in zinc marginal deficient lactating mothers is needed to assess the impact of zinc supplementation on milk zinc concentrations.