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 ((beta) over cap) was estimated for each individual study, and pooled meta-analysis undertaken. The overall pooled (beta) over cap 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; I-2 84.5%). An overall <(beta)over cap> of 0.08 means that for every doubling in Zn intake, the difference in Zn serum or plasma concentration is 2((beta) over cap) (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.