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Iron for exercise performance

Goal: What trials of iron used to improve exercise capacity in women and athletes with low iron.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Updated 9 Nov 2026
Dose

16 to 100 mg of elemental iron a day in trials that raised blood iron markers in athletes.[1] A review of female athletes with low ferritin reported better endurance with about 100 mg a day.[2]

Form

Iron by mouth, without other nutrients, in the 2024 review of athletes.[1]

When to take

Every day.[1]

How long

6 to 8 weeks; shorter courses did not raise blood iron markers.[1] Gains in maximal aerobic capacity came after 36 to 126 days.[2]

What studies found

In 18 trials in women of childbearing age, iron raised VO2max by 2.35 mL/kg/min.[3] In 13 studies in athletes, the effect on VO2max was small and not significant.[1] In adults with low iron but no anemia, iron did not improve measured physical capacity.[4]

Ask a doctor first

In athletes, ferritin rose mainly in those who started at 12 µg/L or lower.[1] In menstruating women, iron about doubled the risk of constipation and of loose stools.[5] The US upper limit for adults is 45 mg a day, and doctors sometimes prescribe more to treat iron deficiency anemia.[6]

Ask a doctor before taking iron for sport. A ferritin blood test shows whether iron stores are low.[6]

References

  1. Effects of Oral Iron Supplementation on Blood Iron Status in Athletes: A Systematic Review, Meta-Analysis and Meta-Regression of Randomized Controlled Trials. Šmid AN, Golja P, Hadžić V, Abazović E, Drole K, Paravlic AH Sports Med, 2024. PMID 38407751
  2. Iron deficiency, supplementation, and sports performance in female athletes: A systematic review. Pengelly M, Pumpa K, Pyne DB, Etxebarria N J Sport Health Sci, 2025. PMID 39536912
  3. Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis. Pasricha SR, Low M, Thompson J, Farrell A, De-Regil LM J Nutr, 2014. PMID 24717371
  4. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. Houston BL, Hurrie D, Graham J, Perija B, Rimmer E, Rabbani R, et al. BMJ Open, 2018. PMID 29626044
  5. Daily iron supplementation for improving anaemia, iron status and health in menstruating women. Low MS, Speedy J, Styles CE, De-Regil LM, Pasricha SR Cochrane Database Syst Rev, 2016. PMID 27087396
  6. Iron: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov