The relationship between zinc intake and serum/plasma zinc concentration in pregnant and lactating women: A systematic review with dose–response meta-analyses

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Abstract

Recommendations for zinc intake during pregnancy and lactation vary widely across Europe. Using data on zinc intake and biomarkers of zinc status reported in randomized controlled trials (RCTs) and observational studies can provide estimates of dose–response relationships that may be used for underpinning zinc reference values. This systematic review included all RCTs, prospective cohort studies, nested case–control studies and cross-sectional studies in healthy pregnant and lactating populations published by February 2010 which provided data on zinc intake and biomarkers of zinc status. An intake-status regression coefficient (βˆ) was calculated for each individual study and calculated the overall pooled βˆ and SE (βˆ) using random effects meta-analysis on a double log scale. The pooled dose–response relationship between zinc intake and zinc status found that a doubling of zinc intake was associated with an increase in serum/plasma zinc status by 3% in pregnant women and by 1% in lactating women. These modest associations are likely to reflect the low-moderate zinc bioavailability dietary patterns and the widespread use of other micronutrients in the populations included in this review, physiologic adjustments of zinc homeostasis, insensitivity of serum/plasma zinc as a biomarker of zinc status, and wide heterogeneity between study results which reflect real uncertainty in the current evidence base. Although this review provides useful information for dietary zinc requirements in populations vulnerable to zinc deficiency, it also highlights a need for further studies in pregnant and lactating women with different dietary patterns in order to provide useful complementary evidence that can be utilized when setting zinc recommendations as a basis for nutrition policies in Europe.

Introduction

An adequate zinc status in women who are pregnant or lactating is imperative for the optimal health of both mother and infant but at present the dietary recommendations for zinc during pregnancy and lactation vary widely across Europe. During pregnancy recommendations range from 7 to 20 mg zinc per day in the UK and Spain, respectively [1]. The maternal dietary requirements for zinc during lactation are quantitatively greater than those during pregnancy and recommended intakes range from 10 to 25 mg/day across European countries representing an increase of up to 90% over non-pregnant, non-lactating levels [2]. The European Micronutrient Recommendations Aligned (EURRECA) Network of Excellence project attempts to consolidate the basis for the definition of micronutrient requirements across Europe, taking into account relationships among intake, status and health outcomes, in order to harmonize these recommendations [3]. Understanding the relationship between dietary intake and micronutrient status is essential for deriving dietary recommendations. In addition, when the predictive value of the zinc biomarker data on specific health outcomes is available, a curve modeling the zinc status as a function of intake is informative to determine the zinc intake dose necessary to achieve normal or optimal levels of zinc status. Although a sensitive and specific biomarker has yet to be identified, a recent systematic review concluded that plasma (or serum) zinc concentration was responsive to both zinc supplementation and depletion and is the most widely used biomarker for zinc [4]. However, meta-analytic methods have not yet been used to model zinc status as a function of zinc intake levels. This paper presents a systematic review of the data from all available randomized controlled trials (RCTs) and observational studies meeting EURRECA's quality standard, which investigated zinc intake and biomarkers of zinc status in pregnant and lactating women, and combines these studies in meta-analyses to model zinc concentrations in serum or plasma as a function of zinc intake.

Section snippets

Search strategy

This research was conducted within the EURRECA framework which aims to identify micronutrient requirements for optimal health in European populations (www.eurreca.org). This review was part of a wider review process to identify studies assessing the effect of zinc intake on different outcomes (biomarkers of zinc status and health outcomes). This wider review process involved searches of literature published up to and including February 2010 using MEDLINE, Embase, and Cochrane using search terms

Results

Six RCTs on zinc intake and serum/plasma status in pregnant women were eligible for meta-analysis [5], [6], [7], [10], [15], [16]. None of the observational studies provided sufficient data to be included in a meta-analysis. One RCT included two distinct zinc-treated groups and two control groups [5] and was treated as two independent estimates in the analysis. Therefore seven estimates of zinc intake/status were included in the analysis. These seven estimates included 1530 participants in

Discussion

Data on zinc intake and plasma/serum zinc status were extracted and analyzed from 6 RCTs in pregnancy and 3 RCTs in lactation. The majority of studies reported that zinc supplementation significantly increased zinc plasma/serum status or significantly reduced the number of low serum values in their participants. A meta-analysis of 7 estimates in 6 RCTs during the third trimester of pregnancy and 3 RCTs in lactation provided an estimate of the dose–response relationship between zinc intake and

References (27)

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The work reported herein has been carried out within the EURRECA Network of Excellence (www.eurreca.org) which is financially supported by the Commission of the European Communities, Specific Research, Technology and Development (RTD) Programme Quality of Life and Management of Living Resources within the Sixth Framework Programme, contract no. 036196. This report does not necessarily reflect the Commission's views or its future policy in this area. The original conception of the systematic review was undertaken by the EURRECA Network and coordinated by partners based at Wageningen University (WU), the Netherlands and the University of East Anglia (UEA), UK. Susan Fairweather-Tait (UEA), Lisette de Groot (WU), Pieter van’ t Veer (WU), Kate Ashton (UEA), Amélie Casgrain (UEA), Adriënne Cavelaars (WU), Rachel Collings (UEA), Rosalie Dhonukshe-Rutten (WU), Esmée Doets (WU), Linda Harvey (UEA) and Lee Hooper (UEA) designed and developed the review protocol and search strategy.

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