Gymnastik- och idrottshögskolan, GIH

Introduction: The first period of military service consists of a physically and mentally challenging basic combat training (BCT) program. Factors like demanding physical exercise, limited recovery time, and restricted diet choice and food intake may challenge iron intake and homeostasis in recruits undergoing BCT. Iron-deficient individuals may experience reduced work capacity, fatigue, weakness, frequent infections, and increased injury risk. Limited knowledge is available on the extent of this potential health risk among military recruits. The aim of the present study was to systematically review published studies on the prevalence and change in prevalence of anemia, iron deficiency (ID), and ID anemia (IDA) among recruits undergoing BCT.

Materials and methods: Electronic searches were conducted in the databases Medline (Ovid), Embase (Embase.com), and Web of Science (Clarivate Analytics) from database inception up until April 16, 2024. Inclusion criteria were observational studies with both cross-sectional and observational longitudinal designs that examined the effects of BCT (intervention) on iron status (outcome) in military recruits (population). Extracted data were the number of participants (n), age, sex, country/population, BCT duration, and relevant measures of prevalence and changes in prevalence of anemia, ID, and IDA (primary outcome) and physical performance, mood state, stress fractures, attrition rate, and nutritional supplements (secondary outcomes). The study quality and risk of bias were assessed using the JBI Critical Appraisal Checklist for Studies Reporting Prevalence Data and The National Institutes of Health Quality Assessment Tool for Before-After (Pre-Post) Studies With No Control Group. Meta-analyses were performed using restricted maximum-likelihood models, and the effect size was calculated as Cohen's h with 95% CI.

Results: Twenty-two articles were systematically reviewed (n = 111,764 men and 12,650 women), and six of these papers (n = 388 men and 773 women) were included in the meta-analysis. There was a varying prevalence of anemia, ID, and IDA among military recruits at the start of BCT. Results from meta-analyses showed negligible and nonsignificant effects of BCT on the prevalence of anemia, ID, and IDA. The quality of the included cross-sectional studies ranging from fair to good, whereas a large proportion of the included longitudinal studies were classified as poor. No sign of publication bias was found.

Conclusions: The prevalence of anemia, ID, and IDA in military recruits seems not to be affected by the completion of BCT shorter than 16 weeks, whereas the effects of longer BCT durations remain unclear. Even though body iron homeostasis seems unaffected, adequate energy and nutritional intake should remain a priority. Future research could focus on dietary interventions to determine the optimal diet among female recruits in specifically exposed populations.