Iron for runners: what's being used and what the research says
We report what runners are using and what the research says. We don't recommend taking any supplement. Talk to your GP or a registered sports dietitian before trying one.
Quick answer
Research suggests it can when iron is low, but not otherwise. In iron-deficient female athletes, a systematic review found endurance gains of 2% to 20%[1]. In distance runners whose iron was not low, intravenous iron raised iron stores but not 3,000 m speed[2]. Sports bodies say low iron should be confirmed with tests first[3].
- Research
- Emerging (proposed)Some gains when iron is low, mostly shown in women. No benefit shown when iron stores are normal.
- Proposed by our editor; not yet confirmed by an expert reviewer.
- WADA status
- Permitted
- Distances in the research
- 800 m–5K: limited research10K–half: not studiedMarathon: not studiedUltra: not studied
What is iron?
Iron is a mineral the body needs to make red blood cells, which carry oxygen around the body[4]. Iron tablets come in several types, including ferrous sulfate, ferrous fumarate and ferrous gluconate[5].
The Australian Institute of Sport lists iron in Group A of its framework as a medical supplement rather than a performance supplement[6].
Also called: iron tablets, ferrous sulfate, ferrous fumarate, ferrous gluconate, iron supplements.
Why is iron getting attention?
Low iron is common in endurance athletes, particularly women, according to the international athletics federation's consensus[7]. Reported rates are about 15 to 35% of female athletes and 3 to 11% of males[8].
At the Zurich marathon, 28% of female runners had depleted iron stores, compared with under 2% of men[9]. Of 1,073 women surveyed at the 2015 London Marathon, 45% said they had taken iron at some point, including in multivitamins[10].
How does iron work?
Iron carries oxygen in the blood, so it matters most in events that rely on aerobic energy, from middle distance upwards[11].
Iron can run low for reasons linked to training, such as red blood cells damaged by foot strike and iron lost in sweat, urine and the gut, and for other reasons, such as menstrual losses and low intake[3]. After exercise, hepcidin, the hormone that regulates iron, rises for several hours, which alters how iron is absorbed[12][11].
Does iron improve running performance?
Sometimes, when iron is low. In endurance athletes with low iron but normal haemoglobin, a meta-analysis of 17 studies found iron improved iron status and VO2max[13]. A later meta-analysis of randomised oral iron trials found iron raised ferritin mainly in athletes who started very low and did not significantly improve VO2max; its authors conclude there is no benefit when ferritin is normal[8].
800 m to 5K (Limited research)
In 14 distance runners whose iron was not clinically low, intravenous iron raised iron stores but did not improve 3,000 m time[2]. A systematic review lists an older trial in 12 iron-deficient female runners, in which the 6 given oral iron improved 3,000 m running measures by about 4%[1].
10K to half marathon (Not studied)
We found no iron trials with a 10 km or half-marathon result. Lab studies in distance runners were mixed: in iron-depleted women, 8 weeks of oral iron raised iron stores but not endurance[14], while in runners with the lowest iron, intravenous iron raised VO2max and time to exhaustion[15].
Marathon (Not studied)
We found no iron trials with a marathon result. At the Zurich marathon, 28% of female runners had depleted iron stores, while one in six men had signs of too much iron[9].
Ultra (Not studied)
We found no iron trials in ultra runners. The rise in hepcidin after exercise grows with the length of the session[12].
The key studies, in order
- 1992Trial18 iron-depleted female distance runners: 8 weeks of oral iron raised iron stores, but time to exhaustion did not differ from a placebo. [14]
- 2010Observational study170 Zurich marathon runners: iron stores were depleted in 28% of women and under 2% of men, while one in six men had signs of iron overload. [9]
- 2014Non-randomised trialNon-randomised comparison of intravenous and oral iron in 27 highly trained distance runners: in those with the lowest iron, intravenous iron raised haemoglobin mass, VO2max (3.3%) and time to exhaustion (9.3%). [15]
- 2014Trial14 distance runners without clinical iron deficiency: intravenous iron doubled iron stores but did not improve 3,000 m time. Self-reported fatigue and mood scores improved. [2]
- 2015Meta-analysis17 studies of endurance athletes with low iron but normal haemoglobin: iron treatment improved iron status and had a moderate effect on VO2max. [13]
- 2016Survey1,073 women surveyed at the 2015 London Marathon: 45% said they had taken iron at some point, including in multivitamins. [10]
- 2018ConsensusDeficiencies should be identified before supplementing. Iron taken when stores are already adequate can cause harm. Even vitamin and mineral products have rarely contained banned substances. [3]
- 2019ConsensusCompromised iron status is common in endurance athletes, particularly females. Recommends routine screening; injected iron only in a medical setting under a physician's supervision. [7]
- 2019Expert reviewIron matters most for events that stress the aerobic energy system, from middle distance up. After exercise, a rise in the hormone hepcidin alters iron absorption and recycling. [11]
- 2023Meta-analysisExercise raised hepcidin, the hormone that regulates iron, 1.5 to 2.5-fold, peaking 3 to 6 hours later. The size of the rise depended mostly on how long the session lasted. [12]
- 2024Meta-analysis13 randomised trials, 449 athletes (432 women): oral iron raised ferritin, mostly in those starting at 12 µg/L or below, and did not significantly improve VO2max. The authors see no benefit when ferritin is normal. [8]
- 2025Systematic review23 studies, 669 female athletes: iron deficiency cut endurance performance by 3-4%, and treating it with about 100 mg of iron a day improved endurance by 2-20%. [1]
What the research can't tell us yet
Most participants were women: in the meta-analysis of oral iron trials, 432 of 449 participants were female[8].
The studies were small and defined low iron in different ways, and the quality of evidence ranged from moderate to low[8]. The one runner study with a positive result on VO2max was not randomised and had no placebo group[15].
How is iron used in studies?
The NHS says men need 8.7 mg of iron a day and women aged 19 to 49 need 14.8 mg, and most people can get enough from a varied diet. It says 17 mg or less a day from supplements is unlikely to cause harm, unless a GP advises a higher dose[4].
In a meta-analysis of oral iron trials in athletes, doses that improved iron status ranged from 16 to 100 mg of elemental iron a day, taken for 6 to 8 weeks[8]. The international athletics federation says injected iron should only be given in a medical setting under a doctor's supervision[7].
The NHS advises leaving a 2 hour gap between iron tablets and tea, coffee, dairy products or eggs, which can stop the body absorbing iron[16].
| What studies used | When | Ref. |
|---|---|---|
| 16 to 100 mg of elemental iron a day, by mouth | 6 to 8 weeks, in trials of athletes (meta-analysis) | [8] |
| About 100 mg of elemental iron a day, by mouth | Up to 56 days, in iron-deficient female athletes | [1] |
| Three 100 mg intravenous injections over 4 weeks | Distance runners without clinical iron deficiency | [2] |
What are the side effects, and who should be careful?
The NHS lists constipation, feeling or being sick and stomach pain as side effects of high doses (over 20 mg), and warns that very high doses can be fatal, particularly for children[4].
Darker poo is common and usually nothing to worry about, but the NHS says to talk to a doctor or call 111 straight away if it is black, tar-like or red[17].
The IOC warns that iron taken when stores are already adequate can cause vomiting, diarrhoea and abdominal pain, and can go on to cause iron overload and liver failure[3].
Be careful if
- You feel tired but haven't had a blood test: the NHS says there may be other reasons you lack energy, and to talk to a doctor or pharmacist before taking iron[5].
- You have haemochromatosis, a condition in which iron builds up in the body: the NHS says you'll usually be advised to avoid iron and vitamin C supplements[18].
- You take other medicines, such as antacids, some antibiotics or levothyroxine: they can interact with iron[19].
Is iron allowed in competition?
Iron is not on the World Anti-Doping Agency's Prohibited List. But intravenous infusions or injections of more than 100 mL in 12 hours are a prohibited method, unless legitimately received during hospital treatment, surgery or clinical investigations; otherwise they need a Therapeutic Use Exemption[20].
The IOC notes that even common vitamin and mineral products have, rarely, been found to contain prohibited substances, and athletes are responsible for anything found in their sample[3].
Independent quality-assurance schemes, often called batch testing, check supplement products for prohibited substances[3]. WADA says using a product from one of these schemes can reduce, but not eliminate, the risk of an anti-doping violation[20], and the IOC says no product can be guaranteed entirely safe[3].
Myth or evidence?
5 things runners hear about iron. Pick an answer to see what the research says.
1.Iron supplements make every runner faster.
2.Female runners are more likely to have low iron.
Show the answer
Evidence. At the Zurich marathon, 28% of women had depleted iron stores, against under 2% of men[9].
3.Hard running changes how the body handles iron.
Show the answer
Evidence. Hepcidin, the hormone that regulates iron, rises 1.5 to 2.5-fold after exercise[12].
4.Extra iron is harmless if you don't need it.
5.It doesn't matter what you drink with an iron tablet.
Show the answer
Myth. The NHS advises a 2 hour gap from tea, coffee and dairy, which can stop your body absorbing iron[16].
Have you tried iron?
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Frequently asked questions
- Does iron improve running performance?
- Research suggests it can when iron is low: a meta-analysis found iron improved VO2max in endurance athletes with low iron[13]. In runners whose iron was not low, intravenous iron did not improve 3,000 m time[2].
- Why are female runners more likely to have low iron?
- Menstrual losses add to the ways running lowers iron, such as red blood cells damaged by foot strike and iron lost in sweat[3]. At the Zurich marathon, 28% of women had depleted iron stores, against under 2% of men[9].
- How do I know if my iron is low?
- Sports bodies say deficiency should be identified first, including with blood markers[3]. The NHS says that if you feel tired but haven't been diagnosed, you should talk to a doctor or pharmacist, as there may be other reasons you lack energy[5].
- What side effects can iron tablets cause?
- The NHS lists constipation, feeling or being sick and stomach pain at doses over 20 mg[4]. Darker poo is common, but black, tar-like or red poo needs a doctor or a call to 111[17].
- Can I take iron with coffee or breakfast?
- The NHS advises leaving a 2 hour gap between iron and tea, coffee, dairy products or eggs, which can stop your body absorbing it[16].
- Is iron allowed in sport? What about iron drips?
- Iron is not on the WADA Prohibited List, but infusions or injections of more than 100 mL in 12 hours are a prohibited method unless legitimately received during hospital treatment, surgery or clinical investigations; otherwise they need a Therapeutic Use Exemption[20].
References
- [1]
Pengelly M, Pumpa K, Pyne DB, Etxebarria N Iron deficiency, supplementation, and sports performance in female athletes: a systematic review. Journal of Sport and Health Science, 2025.
Systematic review23 studies, 669 female athletes: iron deficiency cut endurance performance by 3-4%, and treating it with about 100 mg of iron a day improved endurance by 2-20%.
doi.org/10.1016/j.jshs.2024.101009 - [2]
Woods A, Garvican-Lewis LA, Saunders PU, et al. Four weeks of IV iron supplementation reduces perceived fatigue and mood disturbance in distance runners. PLOS ONE, 2014.
Randomised controlled trial14 distance runners without clinical iron deficiency: intravenous iron doubled iron stores but did not improve 3,000 m time. Self-reported fatigue and mood scores improved.
doi.org/10.1371/journal.pone.0108042 - [3]
Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 2018.
Consensus statementDeficiencies should be identified before supplementing. Iron taken when stores are already adequate can cause harm. Even vitamin and mineral products have rarely contained banned substances.
doi.org/10.1136/bjsports-2018-099027 - [4]
NHS Iron: vitamins and minerals. NHS, 2026.
RegulatorMen need 8.7 mg a day and women aged 19 to 49 need 14.8 mg; most people can get enough from their diet. 17 mg or less a day from supplements is unlikely to cause harm.
www.nhs.uk/conditions/vitamins-and-minerals/iron/ - [5]
NHS Common questions about ferrous sulfate. NHS, 2026.
RegulatorOther types of iron include ferrous fumarate and ferrous gluconate. If you feel tired but haven't been diagnosed with low iron, talk to a doctor or pharmacist first: there may be other reasons.
www.nhs.uk/medicines/ferrous-sulfate/common-questions-about-ferrous-sulfate/ - [6]
Australian Institute of Sport AIS Sports Supplement Framework: Group A and linked fact sheets. Australian Sports Commission, 2026.
Consensus statementLists iron in Group A under medical supplements, separately from the performance supplements.
www.ausport.gov.au/ais/nutrition/supplements/group_a - [7]
Burke LM, Castell LM, Casa DJ, et al. International Association of Athletics Federations consensus statement 2019: nutrition for athletics. International Journal of Sport Nutrition and Exercise Metabolism, 2019.
Consensus statementCompromised iron status is common in endurance athletes, particularly females. Recommends routine screening; injected iron only in a medical setting under a physician's supervision.
doi.org/10.1123/ijsnem.2019-0065 - [8]
Šmid AN, Golja P, Hadžić V, et al. Effects of oral iron supplementation on blood iron status in athletes: a systematic review, meta-analysis and meta-regression of randomized controlled trials. Sports Medicine, 2024.
Meta-analysis13 randomised trials, 449 athletes (432 women): oral iron raised ferritin, mostly in those starting at 12 µg/L or below, and did not significantly improve VO2max. The authors see no benefit when ferritin is normal.
doi.org/10.1007/s40279-024-01992-8 - [9]
Mettler S, Zimmermann MB Iron excess in recreational marathon runners. European Journal of Clinical Nutrition, 2010.
Observational study170 Zurich marathon runners: iron stores were depleted in 28% of women and under 2% of men, while one in six men had signs of iron overload.
doi.org/10.1038/ejcn.2010.16 - [10]
Bruinvels G, Burden R, Brown N, et al. The prevalence and impact of heavy menstrual bleeding (menorrhagia) in elite and non-elite athletes. PLOS ONE, 2016.
Survey1,073 women surveyed at the 2015 London Marathon: 45% said they had taken iron at some point, including in multivitamins.
doi.org/10.1371/journal.pone.0149881 - [11]
Castell LM, Nieman DC, Bermon S, et al. Exercise-induced illness and inflammation: can immunonutrition and iron help?. International Journal of Sport Nutrition and Exercise Metabolism, 2019.
Expert reviewIron matters most for events that stress the aerobic energy system, from middle distance up. After exercise, a rise in the hormone hepcidin alters iron absorption and recycling.
doi.org/10.1123/ijsnem.2018-0288 - [12]
Fensham NC, Govus AD, Peeling P, et al. Factors influencing the hepcidin response to exercise: an individual participant data meta-analysis. Sports Medicine, 2023.
Meta-analysisExercise raised hepcidin, the hormone that regulates iron, 1.5 to 2.5-fold, peaking 3 to 6 hours later. The size of the rise depended mostly on how long the session lasted.
doi.org/10.1007/s40279-023-01874-5 - [13]
Burden RJ, Morton K, Richards T, et al. Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis. British Journal of Sports Medicine, 2015.
Meta-analysis17 studies of endurance athletes with low iron but normal haemoglobin: iron treatment improved iron status and had a moderate effect on VO2max.
doi.org/10.1136/bjsports-2014-093624 - [14]
Klingshirn LA, Pate RR, Bourque SP, et al. Effect of iron supplementation on endurance capacity in iron-depleted female runners. Medicine and Science in Sports and Exercise, 1992.
Randomised controlled trial18 iron-depleted female distance runners: 8 weeks of oral iron raised iron stores, but time to exhaustion did not differ from a placebo.
doi.org/10.1249/00005768-199207000-00013 - [15]
Garvican LA, Saunders PU, Cardoso T, et al. Intravenous iron supplementation in distance runners with low or suboptimal ferritin. Medicine and Science in Sports and Exercise, 2014.
Non-randomised trialNon-randomised comparison of intravenous and oral iron in 27 highly trained distance runners: in those with the lowest iron, intravenous iron raised haemoglobin mass, VO2max (3.3%) and time to exhaustion (9.3%).
doi.org/10.1249/MSS.0b013e3182a53594 - [16]
NHS About ferrous sulfate. NHS, 2026.
RegulatorLeave a 2 hour gap before tea or coffee, dairy products or eggs, which can stop the body absorbing iron.
www.nhs.uk/medicines/ferrous-sulfate/about-ferrous-sulfate/ - [17]
NHS Side effects of ferrous sulfate. NHS, 2026.
RegulatorDarker poo is common with iron. Talk to a doctor or call 111 straight away if poo is black, tar-like or red.
www.nhs.uk/medicines/ferrous-sulfate/side-effects-of-ferrous-sulfate/ - [18]
NHS Haemochromatosis: treatment. NHS, 2026.
RegulatorPeople with haemochromatosis are usually advised to avoid iron and vitamin C supplements, which may be harmful for people with high iron levels.
www.nhs.uk/conditions/haemochromatosis/treatment/ - [19]
NHS Taking ferrous sulfate with other medicines and herbal supplements. NHS, 2026.
RegulatorIron interacts with some medicines, including antacids, some antibiotics and levothyroxine.
www.nhs.uk/medicines/ferrous-sulfate/taking-ferrous-sulfate-with-other-medicines-and-herbal-supplements/ - [20]
World Anti-Doping Agency The Prohibited List. World Anti-Doping Agency, 2026.
RegulatorThe substances and methods prohibited in sport. Iron is not on it; infusions or injections over 100 mL in 12 hours are a prohibited method outside hospital care.
www.wada-ama.org/en/prohibited-list
Who wrote and reviewed this
Written by Grant MacMillan, Editor, RunV. Not yet reviewed by an expert.
Last checked against its references . Next review due . How pages are reviewed · How we grade research
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