Methods of assessment of zinc status in humans: an updated review and meta-analysis

Abstract

Background: The assessment of zinc status is difficult, but vitally important for the identification of zinc deficiency and evaluation of interventions to improve zinc status. Objective: The purpose of this systematic review (SR) and meta-analysis was to update the previously published SR of biomarkers of zinc status, conducted by the European Micronutrient Recommendations Aligned (EURRECA) network in 2009, to answer the question: which putative measures (biomarkers) of zinc status appropriately reflect a change in zinc intake over a period of at least two weeks.
Methods: A structured search strategy was used to identify articles published between January 2007 and September 2022 from MEDLINE (OVID), Embase (OVID), Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials (CENTRAL). Relevant articles were identified using previously defined eligibility criteria. Data were extracted and combined with data from the previous SR. A random-effect model was used to calculate pooled mean differences using STATA. The risk of bias and the certainty of evidence for all outcomes were assessed.
Results: Additional data on 7 of the 32 previously reported biomarkers were identified, along with data on an additional 40 putative biomarkers from studies published since 2007. Pooled data analysis confirmed that in healthy participants, both plasma/serum zinc concentration, and urinary zinc excretion responded to changes in zinc intake [plasma/serum: mean effect, (95% CI), controlled studies: 2.17 µmol/L (1.73, 2.61), p<0.005, I2 =97.8; before and after studies: 2.87 µmol/L (2.45, 3.30), p <0.005, I2=98.1%; urine zinc: 0.39 mmol/mol creatinine (0.17, 0.62), p<0.005, I2= 81.2; 3.09 µmol/d (0.16, 6.02), p=0.039, I2= 94.3].
Conclusions: The updated analyses support the conclusion that plasma/serum and urinary zinc respond to changes in zinc intake in studies of healthy participants. Several additional putative biomarkers were identified, but more studies are needed to assess the sensitivity and reliability.