A nutritional supplement containing zinc during preconception and pregnancy increases human milk zinc concentrations

Abstract

Introduction: During pregnancy and lactation minerals such as zinc are required to support maternal and infant health. Zinc is involved in various cellular processes, with requirements increasing in pregnancy and lactation. In the setting of a randomized trial, we investigated the effects on human milk (HM) zinc concentrations of a micronutrient-containing supplement including zinc in the intervention (but not control) group, started preconception and taken throughout pregnancy until birth. Additionally, we characterized longitudinal changes in HM concentrations of zinc and other minerals (calcium, copper, iodine, iron, magnesium, manganese, phosphorus, potassium, selenium, and sodium).

Methods: HM samples were collected across 7 time points from 1 week to 12 months from lactating mothers from Singapore (n = 158) and New Zealand (n = 180). HM minerals were quantified using sector field inductively coupled plasma mass spectrometry. Potential intervention effects on HM mineral concentrations were assessed using linear mixed models with a repeated measures design and time-weighted area-under-the-curve analyses.

Results: Over the first 3 months of lactation, HM zinc concentrations were 11% higher in the intervention group compared to the control group (p = 0.021). Higher HM zinc concentrations were most evident at 6 weeks of lactation. The intervention had no effect on HM concentrations of other minerals, which were not differently supplemented to the control and intervention groups. Temporal changes in HM minerals over 12 months of lactation were studied in the New Zealand mothers; HM zinc and copper concentrations progressively decreased throughout 12 months, while iron, potassium, sodium, and phosphorus decreased until 6 months then plateaued. HM calcium and magnesium initially increased in early lactation and iodine remained relatively constant throughout 12 months. HM manganese and selenium fell over the initial months of lactation, with a nadir at 6 months, and increased thereafter. The contrasting patterns of changes in HM mineral concentrations during lactation may reflect different absorption needs and roles at different stages of infancy.

Discussion: Overall, this study indicates that HM zinc concentrations are influenced by maternal supplementation during preconception and pregnancy. Further studies are required to understand the associations between HM zinc and other minerals and both short- and long-term offspring outcomes.

Trial registration: ClinicalTrials.gov, identifier: NCT02509988, Universal Trial Number U1111-1171-8056. Registered on 16 July 2015. This is an academic-led study by the EpiGen Global Research Consortium.

Keywords: human milk; minerals; pregnancy; supplement; zinc.

Figure 1

CONSORT diagram for number of human milk (HM) samples analyzed for mineral concentrations in the NiPPeR study. Reasons for exclusion during the preconception phase have been published previously (27), while reasons for exclusion during pregnancy and birth in Singapore (SGP) and New Zealand (NZL) are provided in Supplementary Table 2. There were no HM samples collected in the United Kingdom (UK), so all participants from that site were excluded from this diagram. *Number of participants who provided at least one HM sample during 12 months of lactation. ^†Number of participants who provided at least one HM sample during the first 3 months of lactation.

Figure 2

Zinc concentrations in human milk of control () and intervention () groups in the NiPPeR study during the first 3 months of lactation: (A) Overall, (B) Singapore, and (C) New Zealand. Data are the least-squares means (i.e., adjusted means) for each group, adjusted for visit, an interaction term (group*visit), study site, adherence, maternal pre-pregnancy body mass index, and gestational age at birth; error bars represent the respective 95% confidence intervals. *p < 0.01 for the difference between intervention and control groups at a given time point. The number of HM samples per group analyzed at a given time point are provided in the tables below the x axes.

Figure 3

Mineral concentrations in human milk of control () and intervention () groups in the NiPPeR study during the first 3 months of lactation: (A) calcium, (B) copper, (C) iodine, (D) iron, (E) magnesium, (F) manganese, (G) phosphorus, (H) potassium, (I) selenium, and (J) sodium. Data are the least-squares means (i.e., adjusted means) for each group, adjusted for visit, an interaction term (group*visit), study site, adherence, maternal pre-pregnancy body mass index, and gestational age at birth; error bars represent the respective 95% confidence intervals. *p < 0.05 for a difference between intervention and control groups at a given time point. The number of HM samples per group analyzed at a given time point are provided in the tables below the x axes.

Figure 4

Zinc concentrations in human milk from control () and intervention () groups in New Zealand in the NiPPeR study during 12 months of lactation. Data are the least-squares means (i.e., adjusted means) for each group adjusted for visit, a group*visit interaction term, adherence, maternal pre-pregnancy body mass index, and gestational age at birth; error bars represent the respective 95% confidence intervals. The number of HM samples per group analyzed at a given time point are provided in the tables below the x axes.

Figure 5

Mineral concentrations in human milk from control () and intervention () groups in New Zealand in the NiPPeR study during 12 months of lactation: (A) calcium, (B) copper, (C) iodine, (D) iron, (E) magnesium, (F) manganese, (G) phosphorus, (H) potassium, (I) selenium, and (J) sodium. Data are the least-squares means (i.e., adjusted means) for each group adjusted for visit, a group*visit interaction term, adherence, maternal pre-pregnancy body mass index, and gestational age at birth; error bars represent the respective 95% confidence intervals. **p < 0.01 for the difference between intervention and control at a given time point. The number of HM samples per group analyzed at a given time point are provided in the tables below the x axes.