Iron Deficiency Cuts Endurance Performance 3–4% in Female Athletes — Here's the Fix
A systematic review of 23 studies shows iron deficiency meaningfully impairs female athlete performance, and targeted supplementation can reverse it.
Summary
A 2025 systematic review of 23 studies covering 669 high-level female athletes found that iron deficiency (serum ferritin <40 µg/L) reduces endurance performance by 3–4% and may impair maximal aerobic capacity and anaerobic power. Supplementing with approximately 100 mg of elemental iron per day orally, or bi-daily via injection over 8–10 days, improved endurance performance by 2–20% and boosted VO2max by 6–15%. The review spanned 16 sports and highlighted that performance decrements worsen with iron deficiency severity. Most studies were moderate quality with small group sizes, urging caution in generalizing findings beyond aerobic-dominant sports.
Detailed Summary
Iron is essential for erythropoiesis, oxygen transport, and mitochondrial energy production — all critical to athletic performance. Yet up to 60% of female athletes are iron deficient, largely due to menstrual iron losses, high training loads, and dietary inadequacies. Despite this prevalence, the precise performance consequences across diverse sports and iron deficiency stages have been poorly characterized, particularly in high-level female athletes.
This systematic review searched five major databases (MEDLINE, SPORTDiscus, Web of Science, Scopus, CINAHL) and identified 23 eligible studies involving 669 female athletes (mean age 22 years, mean VO2max 49.4 mL/kg/min) across 16 sports. Seven studies examined the effects of iron deficiency on performance without intervention; 16 studies assessed iron supplementation outcomes. Athletes were classified as iron deficient using serum ferritin <40 µg/L, and were required to meet high-level training criteria (VO2max >45 mL/kg/min or >5 h/week training). Study quality was assessed via a modified Downs and Black checklist.
Iron deficiency without anemia (IDNA) was associated with 3–4% reductions in endurance performance and variable impairments in VO2max. Notably, VO2max decrements appeared to scale with iron deficiency severity — mild IDNA showed modest or no change, while iron deficiency anemia (IDA) correlated with more pronounced aerobic capacity losses. Isokinetic strength and anaerobic power were also negatively affected in some studies (ranging –23% to +4%), though findings were inconsistent across sports.
Iron supplementation produced meaningful recovery. Oral supplementation of 100 mg/day of elemental iron for up to 56 days improved endurance performance by 2–20%. VO2max improved by 6–15% following 16–100 mg/day of elemental iron for 36–126 days. Lower-dose supplementation (16–60 mg/day for 42–56 days) enhanced energy efficiency, maximal work rates, and blood lactate dynamics. Parenteral (intravenous/intramuscular) administration of 100 mg bi-daily over 8–10 days was an effective alternative, particularly for rapid repletion. Effects on anaerobic power from supplementation were variable (–5% to +9%), underscoring that iron's role beyond aerobic metabolism is less predictable.
The review carries important caveats. Most studies (n=18) had group sizes of 20 or fewer athletes, limiting statistical power. Serum ferritin alone is an imperfect marker of iron status, as it is an acute-phase reactant elevated by inflammation. Study heterogeneity in supplementation dose, duration, route, and athlete classification prevented meta-analysis. Nonetheless, the consistent signal across diverse studies supports clinical action: high-level iron-deficient female athletes should seek evaluation from a sports medicine practitioner or dietitian, with supplementation tailored to deficiency stage, sport demands, and anti-doping compliance.
Key Findings
- Iron deficiency reduces endurance performance by 3–4% in high-level female athletes.
- Oral supplementation of ~100 mg/day elemental iron for up to 56 days improved endurance by 2–20%.
- VO2max improved by 6–15% with iron supplementation of 16–100 mg/day over 36–126 days.
- Isokinetic strength and anaerobic power were inconsistently affected, ranging from –23% to +4%.
- Performance decrements track with iron deficiency severity — anemic athletes show the greatest impairment.
Methodology
Systematic review (PRISMA) of 23 studies from 5 databases; included high-level female athletes (VO2max >45 mL/kg/min or >5 h/week training) with serum ferritin <40 µg/L. Quality assessed via modified Downs and Black checklist (21 items); meta-analysis was precluded by high methodological heterogeneity.
Study Limitations
Most studies had small samples (≤20 athletes), limiting statistical power to detect meaningful effects. Serum ferritin as a sole biomarker for iron deficiency is susceptible to exercise-induced inflammation, creating day-to-day variability. High heterogeneity across supplementation protocols, sport types, and athlete classification systems prevented pooled meta-analysis.
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