Overnutrition is a risk factor for iron deficiency in children and young people: a systematic review and meta-analysis of micronutrient deficiencies and the double burden of malnutrition

Introduction Traditionally associated with undernutrition, increasing evidence suggests micronutrient deficiencies can co-exist with overnutrition. Therefore, this work aimed to systematically review the associations between iron, zinc and vitamin A status and weight status (both under- and overweight) in children and young people. Methods Ovid Medline, Ovid Embase, Scopus, and Cochrane databases were systematically searched for observational studies assessing micronutrient status (blood, serum, or plasma levels of iron, zinc, or vitamin A biomarkers) and weight status (body mass index or other anthropometric measurement) in humans under 25 years of any ethnicity and gender. Risk of bias assessment was conducted using the American Dietetic Association Quality Criteria Checklist. Where possible, random effects restricted maximum likelihood (REML) meta-analyses were performed. PROSPERO (CRD42020221523). Results After screening, 83 observational studies involving 190,443 participants from 44 countries were identified, with many studies having reported on more than one micronutrient and/or weight status indicator. Iron was the most investigated micronutrient, with 46, 28, and 27 studies reporting data for iron, zinc, and vitamin A status, respectively. Synthesizing 16 records of odds ratio (OR) from 7 eligible studies, overnutrition (overweight and obesity) increased odds of iron deficiency (OR [95%CI]: 1.51 [1.20, 1.82], p<0.0001, I2=40.7%). Odds appeared to be higher for children living with obesity (1.88 [1.33, 2.43], p<0.0001 I2=20.6%) in comparison to those with overweight (1.31 [0.98, 1.64], p<0.0001 I2=40.5%), although between group differences were not significant (p=0.08). Conclusions Overnutrition is associated with increased risk of iron deficiency, but not zinc or vitamin A deficiencies, with an inverted U-shaped relationship observed between iron status and bodyweight. Our results highlight significant heterogeneity in the reporting of micronutrient biomarkers and how deficiencies were defined. Inflammation status was rarely adequately accounted for, and the burden of iron deficiency may well be under-recognised, particularly in children and young people living with overnutrition. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Protocols ### Funding Statement This research was funded by the project titled Addressing micronutrient deficiencies associated with the double burden of childhood malnutrition in China, a combined food system framework; BB/T008989/1 from UK Biotechnology and Biological Sciences Research Council (BBSRC). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present work are contained in the manuscript