Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis.
Animal and human observational studies suggest that iron deficiency impairs physical exercise performance, but findings from randomized trials on the effects of iron are equivocal. Iron deficiency and anemia are especially common in women of reproductive age (WRA). Clear evidence of benefit from iron supplementation would inform clinical and public health guidelines. Therefore, we performed a systematic review and meta-analysis to determine the effect of iron supplementation compared with control on exercise performance in WRA. We searched the Cochrane Central Register of Clinical Trials, MEDLINE, Scopus (comprising Embase and MEDLINE), WHO regional databases, and other sources in July 2013. Randomized controlled trials that measured exercise outcomes in WRA randomized to daily oral iron supplementation vs. control were eligible. Random-effects meta-analysis was used to calculate mean differences (MDs) and standardized MDs (SMDs). Risk of bias was assessed using the Cochrane risk-of-bias tool. Of 6757 titles screened, 24 eligible studies were identified, 22 of which contained extractable data. Only 3 studies were at overall low risk of bias. Iron supplementation improved both maximal exercise performance, demonstrated by an increase in maximal oxygen consumption (VO2 max) [for relative VO2 max, MD: 2.35 mL/(kg ⋅ min); 95% CI: 0.82, 3.88; P = 0.003, 18 studies; for absolute VO2 max, MD: 0.11 L/min; 95% CI: 0.03, 0.20; P = 0.01, 9 studies; for overall VO2 max, SMD: 0.37; 95% CI: 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; 95% CI: -7.25, -0.85; P = 0.01, 6 studies) and proportion of VO2 max (MD: -2.68%; 95% CI: -4.94, -0.41; P = 0.02, 6 studies) required to achieve defined workloads. Daily iron supplementation significantly improves maximal and submaximal exercise performance in WRA, providing a rationale to prevent and treat iron deficiency in this group. This trial was registered with PROSPERO (http://www.crd.york.ac.uk/PROSPERO/prospero.asp) as CRD42013005166.
Nossal Institute for Global Health, School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, VIC, Australia Medical Research Council (MRC) Human Immunology Unit, MRC Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, UK sant-rayn.pasricha@unimelb.edu.au.
Sant-Rayn
SR
Pasricha
Department of Clinical Haematology and Bone Marrow Transplant, The Alfred Hospital, Melbourne, VIC, Australia.
Michael
M
Low
School of Medicine, Faculty of Health Sciences, University of Adelaide, Adelaide, SA, Australia.
Jane
J
Thompson
Monash Health, Clayton, VIC, Australia; and.
Ann
A
Farrell
The Micronutrient Initiative, Ottawa, ON, Canada.
Luz-Maria
LM
De-Regil
D018798:Anemia, Iron-Deficiency / Q000188:drug therapy / Q000517:prevention & control; D019587:Dietary Supplements; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D019266:Iron, Dietary / Q000008:administration & dosage*; D064887:Observational Studies as Topic; D010101:Oxygen Consumption; D016032:Randomized Controlled Trials as Topic; D012098:Reproduction / Q000187:drug effects*
D019266:Iron, Dietary