Factors that affect zinc bioavailability and losses in adult and elderly populations.

The most widely used method for estimating dietary zinc requirements is the factorial approach, in which it is assumed, in adults, that the physiological zinc requirement is the lowest intake that replaces endogenous zinc losses. Presented here are the results of two reviews: a narrative review of zinc losses from the human body and a systematic review of factors affecting zinc bioavailability in adult and elderly populations. The narrative review presents data on losses from integumental and excretory routes, obtained from 29 papers published up to April 2013. The systematic review includes a total of 87 publications describing dietary factors that impact zinc bioavailability, 30 of which examined phytate. A meta-analysis revealed an overall lowering of fractional zinc absorption by 0.14 (45% of control values) when the phytate : zinc molar ratio of the test meal or diet was greater than 15. These reviews provide a comprehensive resource for use in the setting of human dietary zinc requirements and emphasize the need for more high-quality data to improve estimates of zinc losses and gains.

The relationship between zinc intake and serum/plasma zinc concentration in adults: a systematic review and dose-response meta-analysis by the EURRECA Network.

Dietary Zn recommendations vary widely across Europe due to the heterogeneity of approaches used by expert panels. Under the EURopean micronutrient RECommendations Aligned (EURRECA) consortium a protocol was designed to systematically review and undertake meta-analyses of research data to create a database that includes 'best practice' guidelines which can be used as a resource by future panels when setting micronutrient recommendations. As part of this process, the objective of the present study was to undertake a systematic review and meta-analysis of previously published data describing the relationship between Zn intake and status in adults. Searches were performed of literature published up to February 2010 using MEDLINE, Embase and the Cochrane Library. Data extracted included population characteristics, dose of Zn, duration of study, dietary intake of Zn, and mean concentration of Zn in plasma or serum at the end of the intervention period. An intake-status regression coefficient (ß ) was estimated for each individual study, and pooled meta-analysis undertaken. The overall pooled ß for Zn supplementation on serum/plasma Zn concentrations from randomised controlled trials and observational studies was 0·08 (95 % CI 0·05, 0·11; P < 0·0001; I² 84·5 %). An overall ß of 0·08 means that for every doubling in Zn intake, the difference in Zn serum or plasma concentration is ß (2(0·08) = 1·06), which is 6 %. Whether the dose-response relationship, as provided in the present paper, could be used as either qualitative or quantitative evidence to substantiate the daily Zn intake dose necessary to achieve normal or optimal levels of biomarkers for Zn status remains a matter of discussion.

The relationship between zinc intake and serum/plasma zinc concentration in children: a systematic review and dose-response meta-analysis.

Recommendations for zinc intake during childhood vary widely across Europe. The EURRECA project attempts to consolidate the basis for the definition of micronutrient requirements, taking into account relationships among intake, status and health outcomes, in order to harmonise these recommendations. Data on zinc intake and biomarkers of zinc status reported in randomised controlled trials (RCTs) can provide estimates of dose-response relationships which may be used for underpinning zinc reference values. This systematic review included all RCTs of apparently healthy children aged 1-17 years published by February 2010 which provided data on zinc intake and biomarkers of zinc status. An intake-status regression coefficient (ß) was calculated for each individual study and calculated the overall pooled and SE (ß) using random effects meta-analysis on a double log scale. The pooled dose-response relationship between zinc intake and zinc status indicated that a doubling of the zinc intake increased the serum/plasma zinc status by 9%. This evidence can be utilised, together with currently used balance studies and repletion/depletion studies, when setting zinc recommendations as a basis for nutrition policies.