Toward revising dietary zinc recommendations for children aged 0-3 years: a systematic review and meta-analysis of zinc absorption, excretion and needs for growth

Abstract

Context The Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) are updating their dietary zinc recommendations for children aged 0-3 years.
Objective
Retrieve and synthesise available evidence regarding zinc needs for growth, zinc losses, absorption, and bioavailability from the diet, needed to update dietary zinc recommendations.
Data Sources
Search of the literature was undertaken, from inception to August 2020, in MEDLINE, EMBASE and the Cochrane Library. Studies assessing the above factors in healthy children aged 0-9 years were included with no study design or language limit.
Data extraction:
Ninety-four studies reporting on endogenous zinc losses via urine, faeces, or integument (N=40); zinc content in tissue (N=27); absorption (N=47) and factors affecting zinc bioavailability (N=30) met the inclusion criteria. Data was extracted by four reviewers and checked for accuracy by two reviewers.
Data Analyses:
Studies were synthesised narratively, meta-analyses were undertaken for zinc losses and gains, subgrouping by age, feeding type, country’s income, and P:Zn molar ratio. The Joanna Briggs Institute (JBI) Critical Appraisal Checklist, Cochrane Risk of Bias (RoB), and Grading of Recommendations Assessment, Development and Evaluation (GRADE) guideline were employed to assess the risk of bias and to appraise the quality of the generated evidence. Meta-analysis of data revealed an overall mean [95% CI] urinary and endogenous faecal (EFZ) excretion of 17.48 µg/kg/d [11.80,23.15], I2=94% and 0.07 mg/kg/d [0.06,0.08], I2=82% respectively, with a mean fractional zinc absorption (FZA) of 26.75% [23.69,29.81], I2=99%. Subgrouping by age revealed differences in mean values associated with the transition from milk-based diets to solid food during the first three years of life.
Conclusion: This review synthesises data that may be used to formulate zinc requirements in young children. Caution is required in interpreting the results of the meta-analyses due to considerable heterogeneity in the evidence.
Systematic review registration
PROSPERO registration no. CRD42020215236