Effects of Daily Iron Supplementation on Physical Performance in Women of Reproductive Age: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Abstract

Objectives: Animal and human observational studies suggest iron deficiency impairs physical exercise performance but findings from randomized trials are conflicting. Iron deficiency and anaemia are especially common in women of reproductive age (WRA). We therefore performed a systematic review and meta-analysis to determine the effect of iron supplementation on exercise performance in WRA. Methods: We searched the Cochrane Central Register of Clinical Trials, MEDLINE, Scopus (comprising Embase and MEDLINE), WHO regional databases and other sources in July 2013. Randomised controlled trials that measured exercise outcomes in WRA randomized to daily oral iron supplementation versus control were eligible. Random-effects meta-analysis was used to calculate Mean Differences (MD) and Standardised MDs (SMD). Risk of bias was assessed using the Cochrane risk-of-bias tool. Results: Of 6757 titles screened, 22 eligible studies contained extractable data. Only 3 were at overall low risk of bias. Iron supplementation improved both maximal exercise performance, demonstrated by an increase in VO2 max (relative VO2 max: MD 2.35 mL/kg/min [95% CI 0.82, 3.88], P=0.003, 18 studies; absolute VO2 max: MD 0.11 L/min [0.03, 0.20], P=0.01, 9 studies; overall VO2 max: SMD 0.37 [0.11, 0.62] P=0.005, 20 studies), and submaximal exercise performance demonstrated by a lower heart rate (MD -4.05 beats per minute [-7.25, -0.85], P=0.01, 6 studies) and proportion of VO2 max (MD -2.68% [-4.94, -0.41], P=0.02, 6 studies) required to achieve defined workloads. Conclusions: Daily iron supplementation improves maximal and submaximal exercise performance in WRA, providing a rationale to prevent and treat iron deficiency in this group.