Does iron supplementation help athletes?

It helps the athletes whose iron is low, and the evidence that it helps anyone else is weak. In a 2014 meta-analysis of trials in women of reproductive age, daily oral iron raised relative VO2max by 2.35 mL/kg/min across 18 studies. A 2024 meta-analysis of 13 randomized trials in 449 healthy athletes found oral iron raised ferritin, while the gain in VO2max did not reach statistical significance.

Established. In iron-deficient athletes without anemia, a 2015 meta-analysis of 17 studies found iron treatment moderately improved VO2max, with a standardized effect (Hedges g) of 0.61. The pooled studies mixed tablets and injections, and the abstract does not grade their quality.

What the trials found

The pattern across the pooled analyses is consistent once you sort people by their starting iron. The 2014 review covered women of reproductive age, anemic and not, athletes and not. Only 3 of its 24 studies were at low risk of bias overall. Besides VO2max, heart rate at a fixed workload fell by 4.05 beats per minute.

The 2024 review is the one closest to the question as most people ask it. It took only healthy, physically active adults using oral iron. The VO2max effect was a standardized difference of 0.49 with a confidence interval from -0.09 to 1.07, a trend that did not reach significance, on evidence graded moderate to low. The doses that moved blood markers ranged from 16 to 100 mg of elemental iron a day, taken for 6 to 8 weeks.

A 2018 systematic review sharpened the threshold. Across 12 studies in 283 iron-deficient athletes without anemia, performance improved in six studies and not in the other six. All six positive studies treated athletes whose ferritin was 20 mcg/L or lower. The authors call the evidence equivocal and did not pool it.

Unsettled. Above that line the trials mostly come up empty. In 65 teenage basketball players with ferritin under 100 mcg/L, three months of 100 mg iron left VO2max at 53.6 against 54.4 mL/kg/min on placebo. One 500 mg iron injection in 15 elite iron-deficient runners did not change VO2max or time to exhaustion after four weeks. In 14 distance runners with ferritin of 30 to 100 mcg/L, injected iron improved fatigue and mood scores with no change in performance. All three trials are small, and two of them enrolled people with ferritin well above 20 mcg/L, the level at which the positive studies in the 2018 review treated.

Two more results come from people outside sport. A 2022 abridged Cochrane review of 21 trials with 3514 adults who were iron-deficient without anemia found intravenous iron raised peak oxygen uptake by 1.77 mL/kg/min. The reviewers rated most outcomes low or very low quality, and most participants were patients. In 73 untrained iron-depleted women, 42 mg of iron a day for eight weeks raised VO2peak by 1.87 mL/kg/min (95% CI 0.15 to 3.60). Their estimated VO2max did not change significantly.

For iron status itself the answer is clearer. A 2026 meta-analysis in active women found ferrous sulfate raised hemoglobin by 0.42 g/dL and ferritin by 12.6 ng/mL, with moderate heterogeneity. That review reports no pooled effect on performance.

Who should be careful

Not for everyone. The IOC consensus treats iron as a supplement for after a deficiency has been found. It warns that iron in athletes whose stores are already adequate can cause vomiting, diarrhea and abdominal pain, and over time hemochromatosis and liver failure. The NIH sets the upper intake level at 45 mg a day for adults and 40 to 45 mg for children and teens. Trial doses of 100 mg a day exceed that level, and they were given after blood tests under supervision.

The form matters for the gut. In a 12-week trial of 57 exercising women with ferritin under 50 mcg/L, ferrous sulfate raised ferritin by 109% against 7% with a polymaltose iron. It also caused more gut symptoms, in 33% of women against 28%. That trial was single-blind and had no placebo arm.

What expert bodies say

The IOC consensus statement names iron, with calcium and vitamin D, among the nutrients athletes often need to supplement once a full nutritional assessment has found a deficiency. It does not give the same advice to athletes whose stores are adequate. The NIH upper limit above applies to everyone.

How we searched

What would change this answer

• Large placebo-controlled trials in athletes split by starting ferritin, 20 mcg/L or lower against 20 to 50 mcg/L, with a timed performance test as the outcome. Most trials so far measured VO2max in small groups.
• Results from two registered trials, one of iron with curcumin and one on correcting deficiency in college athletes. Both are listed as completed with no results posted.

More on the mineral itself is in our iron guide.

Sources

1. ev-feath-01 · Meta-analysis or systematic review · systematic review and random-effects meta-analysis of RCTs · n = 18 studies
   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.
   
   Who: women of reproductive age randomized to daily oral iron versus control; 22 studies with extractable data
   Effect: relative VO2max MD 2.35 mL/(kg min) (95% CI 0.82 to 3.88; 18 studies); absolute VO2max MD 0.11 L/min (0.03 to 0.20); submaximal heart rate MD -4.05 bpm (-7.25 to -0.85)
   Certainty: Only 3 of 24 studies at overall low risk of bias; includes non-athletes and anemic women.
   J Nutr, 2014 · checked 2026-10-07 · we read the abstract
2. ev-feath-02 · Meta-analysis or systematic review · systematic review and meta-analysis · n = 17 studies
   Analysis of pooled data indicated that iron treatments had a large effect on improving sFer (Hedges' g=1.088, 95% CI 0.914 to 1.263, p<0.001), sFe (Hedges' g=1.004, 95% CI 0.828 to 1.181, p<0.001) and Tsat (Hedges g=0.741, 95% CI 0.564 to 0.919, p<0.001) and a moderate effect on improving [Hb] (Hedges' g=0.695, 95% CI 0.533 to 0.836, p<0.001) and (VO(2max)) (Hedges' g=0.610, 95% CI 0.399 to 0.821, p<0.001).
   
   Who: iron-deficient non-anemic endurance athletes treated with iron
   Effect: VO2max Hedges g 0.610 (95% CI 0.399 to 0.821); serum ferritin g 1.088 (0.914 to 1.263); hemoglobin g 0.695 (0.533 to 0.836)
   Certainty: Mixed oral and parenteral treatments; standardized effect only; quality grading not reported in the abstract.
   Br J Sports Med, 2015 · checked 2026-10-07 · we read the abstract
3. ev-feath-03 · Meta-analysis or systematic review · systematic review, meta-analysis and meta-regression of RCTs · n = 449
   Following OIS, a trend of small positive effect on VO2max (SMD = 0.49, 95% CI - 0.09 to 1.07, p = 0.086) was observed in young healthy athletes.
   
   Who: healthy adult physically active people using oral iron only, any sex or sport
   Effect: serum ferritin SMD 1.27 (95% CI 0.44 to 2.10); hemoglobin SMD 1.31 (-0.29 to 2.93, NS); VO2max SMD 0.49 (-0.09 to 1.07, p=0.086)
   Certainty: GRADE moderate to low for all outcomes.
   Sports Med, 2024 · checked 2026-10-07 · we read the abstract
4. ev-feath-04 · Meta-analysis or systematic review · systematic review, meta-analysis and meta-regression of RCTs · n = 449
   The doses of OIS, that induced a beneficial effect on hematological parameters differed from 16 to 100 mg of elementary iron daily, over the period between 6 and 8 weeks.
   
   Who: healthy adult athletes in 13 RCTs of oral iron
   Effect: doses with a beneficial effect on hematological parameters: 16-100 mg elemental iron/day for 6-8 weeks
   Certainty: Meta-regression across trials; GRADE moderate to low.
   Sports Med, 2024 · checked 2026-10-07 · we read the abstract
5. ev-feath-05 · Meta-analysis or systematic review · systematic review and random-effects meta-analysis of interventional trials · n = —
   Oral iron supplementation in the form of ferrous sulfate resulted in a significant increase in hemoglobin (mean difference [MD] = 0.42 g/dL; 95% confidence interval [CI]: 0.10 to 0.74; p = 0.0109; I2 = 56.6%) and ferritin (MD = 12.61 ng/mL; 95% CI: 8.29 to 16.92; p < 0.0001; I2 = 57.38%).
   
   Who: active females of reproductive age in interventional trials of diet or supplements
   Effect: hemoglobin MD 0.42 g/dL (95% CI 0.10 to 0.74; I2 56.6%); ferritin MD 12.61 ng/mL (8.29 to 16.92; I2 57.38%)
   Certainty: Iron-status outcomes only; abstract reports no pooled performance effect; moderate heterogeneity.
   Sports Med, 2026 · checked 2026-10-07 · we read the abstract
6. ev-feath-06 · Meta-analysis or systematic review · systematic review without pooling · n = 283
   In the 6 studies that showed improved performance with iron supplementation, all used a ferritin level cutoff of ≤20 μg/L for treatment.
   
   Who: iron-deficient non-anemic athletes in level 1 to 3 studies
   Effect: performance improved in 6 studies (146 participants), not in 6 (137); all positive studies treated at ferritin <=20 mcg/L with oral iron
   Certainty: Authors call the evidence equivocal; no meta-analysis.
   Sports Health, 2018 · checked 2026-10-07 · we read the abstract
7. ev-feath-07 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs (Cochrane update) · n = 3514
   Intravenous iron compared with placebo resulted in significantly increased physical function measured by mean peak oxygen consumption (mean difference [MD] 1.77 mL/kg/min, 95% confidence interval [CI] 0.57 to 2.97).
   
   Who: adults with non-anemic iron deficiency, IV iron versus placebo
   Effect: peak VO2 MD 1.77 mL/kg/min (95% CI 0.57 to 2.97)
   Certainty: Quality rated low or very low for most outcomes; mostly patients, not athletes.
   J Cachexia Sarcopenia Muscle, 2022 · checked 2026-10-07 · we read the abstract
8. ev-feath-08 · Randomized controlled trial(s) · double-blind placebo-controlled RCT · n = 40
   At the beginning of a training season, 40 rowers were randomized to receive either 100 mg·d FeSO4 (n = 21) or placebo (n = 19) using a double-blind design.
   
   Who: non-anemic female rowers with depleted iron stores during training; 31 completed
   Effect: design only in the quoted sentence: 21 on ferrous sulfate, 19 on placebo; outcomes not carded
   Certainty: Small trial with dropout; 4-km time trial not reported as improved.
   Med Sci Sports Exerc, 2014 · checked 2026-10-07 · we read the abstract
9. ev-feath-09 · Randomized controlled trial(s) · double-blind placebo-controlled RCT · n = 15
   There were no differences between groups in red cell indices, total hemoglobin mass, V˙O2max, submaximal blood lactate, running economy, RPE, or time to exhaustion (P > 0.05).
   
   Who: national and international standard runners, iron-deficient non-anemic
   Effect: no difference in VO2max, hemoglobin mass, running economy or time to exhaustion at 4 weeks
   Certainty: Very small trial; single injection; 4-week follow-up.
   Med Sci Sports Exerc, 2015 · checked 2026-10-07 · we read the abstract
10. ev-feath-10 · Randomized controlled trial(s) · randomized placebo-controlled trial · n = 65
    There were no differences in performance between the groups (VO2 max: 53.6 ± 4.3 vs. 54.4 ± 5.7 mL/kg/min, p = .46; peak lactate: 9.1 ± 2.2 vs. 9.1 ± 2.6 mmol/L, p = .90).
    
    Who: young male basketball players aged about 16 years, ferritin <100 mcg/L
    Effect: ferritin 75.5 vs 54.9 mcg/L; VO2max 53.6 vs 54.4 mL/kg/min (p=0.46); peak lactate 9.1 vs 9.1 mmol/L
    Certainty: Most players were only mildly iron-deficient by a high cutoff.
    Clin Cardiol, 2023 · checked 2026-10-07 · we read the abstract
11. ev-feath-11 · Randomized controlled trial(s) · double-blind 2x2 factorial RCT · n = 73
    There was no beneficial effect of iron supplementation for VO2max (mean difference: 0.53; 95% CI: -0.75, 1.81; P = 0.42), but a significant benefit was observed for VO2peak (mean difference: 1.87; 95% CI: 0.15, 3.60; P = 0.03).
    
    Who: sedentary iron-depleted non-anemic women aged 18 to 26, ferritin <25 mcg/L
    Effect: VO2peak MD 1.87 (95% CI 0.15 to 3.60); estimated VO2max MD 0.53 (-0.75 to 1.81, NS)
    Certainty: Not athletes; shows effect in iron-depleted women starting training.
    J Nutr, 2019 · checked 2026-10-07 · we read the abstract
12. ev-feath-12 · Randomized controlled trial(s) · blinded placebo-controlled RCT · n = 14
    CONCLUSION: During 6 weeks of training, intravenous iron supplementation improved perceived fatigue and mood of trained athletes with no clinical iron deficiency, without concurrent improvements in oxygen transport capacity or performance.
    
    Who: distance runners without clinical iron deficiency
    Effect: 3,000 m time unchanged (625.6 to 625.4 s); fatigue score ES -1.54 vs placebo at week 6; mood disturbance ES -1.58
    Certainty: Very small trial analyzed with magnitude-based inference.
    PLoS One, 2014 · checked 2026-10-07 · we read the abstract
13. ev-feath-13 · Randomized controlled trial(s) · single-blind RCT · n = 57
    FS was superior in repleting ferritin concentrations after 12 weeks compared with IPC; however, FS also resulted in a greater number and severity of GI symptoms than IPC.
    
    Who: exercising women (athlete, premenopausal and postmenopausal cohorts) with serum ferritin <50 mcg/L
    Effect: ferritin +109% with ferrous sulfate vs +7% with polymaltose complex; symptom rate 33% vs 28%
    Certainty: Active comparator, no placebo; single-blind.
    Clin Nutr, 2026 · checked 2026-10-07 · we read the abstract
14. ev-feath-14 · Position of an expert body · consensus statement · n = —
    For example, iron supplementation in those with already adequate iron stores can result in symptoms that may begin with vomiting, diarrhoea and abdominal pain, and develop to haemochromatosis and liver failure.
    
    Who: high-performance athletes
    Effect: iron listed among nutrients often needing supplementation after assessment; harm when stores are already adequate
    Certainty: Expert consensus; no own pooled analysis.
    Br J Sports Med, 2018 · checked 2026-10-07 · we read the fulltext
15. ev-feath-15 · Position of an expert body · consensus statement · n = —
    Nutrients that often need to be supplemented under these circumstances include iron, calcium and vitamin D (table 1).
    
    Who: high-performance athletes after nutritional assessment
    Effect: supplement only after a complete nutritional assessment
    Certainty: Position of a sports body; no effect size.
    Br J Sports Med, 2018 · checked 2026-10-07 · we read the fulltext
16. ev-feath-16 · Position of an expert body · agency fact sheet · n = —
    The Tolerable Upper Intake Level for iron is 45 mg for adults, and it ranges from 40 mg to 45 mg for infants, children, and adolescents, depending on age.
    
    Who: General population, NIH Office of Dietary Supplements iron fact sheet
    Effect: UL 45 mg/day adults, 40-45 mg/day for infants, children and adolescents
    Certainty: Trial doses of 100 mg/day exceed the UL and are given after blood tests under supervision.
    NIH Office of Dietary Supplements, Iron fact sheet for health professionals · checked 2026-10-07 · we read the section