CICoach ImpactOS

Evidence Lab

Iron

Iron is essential for oxygen transport and energy metabolism. Supplementation can improve iron status and aerobic capacity in iron-deficient athletes, but iron should not be used as a routine performance supplement without evidence of need.

Evidence rating: Strong

Published 8/14/2026 | Last reviewed 8/14/2026

Overview

Iron is a component of hemoglobin, myoglobin and many enzymes involved in energy metabolism. Athletes can be vulnerable to low iron stores because of menstrual blood loss, low energy availability, restrictive diets, gastrointestinal losses, foot-strike hemolysis and increased training demands. The evidence based use of iron supplementation is targeted treatment of deficiency. Meta-analysis in iron-deficient, non-anemic endurance athletes shows that iron treatment can improve iron status and can improve maximal aerobic capacity. More recent reviews in female athletes similarly support a performance cost of iron deficiency and benefit when deficiency is corrected. This does not justify routine iron supplementation in athletes with adequate status. Excess iron causes gastrointestinal effects, can be toxic, and is particularly inappropriate in iron-overload disorders. Ferritin, hemoglobin and the broader clinical picture should guide treatment rather than fatigue alone.

Common use

Prevention or treatment of iron deficiency under appropriate nutrition or clinical guidance; not a routine ergogenic supplement for iron-replete athletes.

Common forms

Ferrous sulfate, ferrous fumarate, ferrous gluconate, iron bisglycinate and other oral forms; intravenous iron is a medical treatment, not a general supplement strategy.

Practical notes

Suspected deficiency should be evaluated with appropriate blood tests and clinical context. Dietary iron, menstrual history, energy availability and gastrointestinal issues can matter. Last evidence review: 14 August 2026.

Claim-level evidence

Strong

Iron supplementation can improve iron status and may improve aerobic capacity in iron-deficient athletes.

Population: Iron-deficient athletes, including iron-deficient non-anemic endurance athletes.

Correct documented deficiency because it can meaningfully affect training and performance.

Limitations: Benefit depends on baseline deficiency, treatment response and the outcome measured.

Strong

Routine iron supplementation is not an evidence based performance strategy for iron-replete athletes.

Population: Athletes with adequate iron status.

Test and identify need rather than supplementing blindly.

Limitations: Iron status markers can be affected by inflammation and training load, so interpretation requires context.

Strong

Female endurance athletes are an important risk group for iron deficiency.

Population: Female athletes, especially with menstrual blood loss, high training volume, low energy availability or low dietary iron.

Include iron-risk screening in nutrition and health review when signs or risk factors are present.

Limitations: Risk is individualized and not every female athlete requires supplementation.

Dosing context

  • General adult intake context - NIH ODS lists an RDA of 8 mg/day for adult men and postmenopausal women and 18 mg/day for premenopausal adult women. - Across meals and food intake. - Ongoing nutritional intake.Vegetarian diets generally require more dietary iron because nonheme iron is less bioavailable.
  • Deficiency treatment context - Treatment doses commonly exceed the RDA and should be individualized to laboratory status, tolerance and the cause of deficiency. - Often separated from inhibitors of absorption; exact scheduling depends on the product and treatment plan. - Usually weeks to months with follow-up testing.Do not use the adult UL as a treatment target; clinician-directed treatment can appropriately exceed it.
  • Adult safety ceiling - Tolerable upper intake level: 45 mg/day from all sources for adults. - Across the day. - Chronic unsupervised intake.The UL does not apply to clinician-supervised treatment of iron deficiency.

Safety notes

  • Iron overload and hemochromatosisPeople with hereditary hemochromatosis or other iron-overload conditions should avoid unsupervised iron supplements because excess iron can damage organs.
  • Gastrointestinal adverse effectsOral iron commonly causes nausea, constipation, abdominal discomfort and dark stools. Tolerability can influence form and schedule.
  • Accidental poisoningIron overdose can be life-threatening, particularly in children. Keep supplements securely stored and seek emergency care for suspected overdose.
  • Unexplained fatigue or anemiaFatigue has many causes and anemia is not always due to iron deficiency. Appropriate testing is required before high-dose treatment.

Interactions

  • LevothyroxineIron can reduce levothyroxine absorption when taken together; dosing separation and thyroid monitoring may be needed.
  • Levodopa and levodopa/carbidopaIron can reduce absorption of levodopa products; follow prescribing or pharmacy guidance on separation.
  • Proton-pump inhibitors and low gastric acidReduced gastric acidity can impair absorption of nonheme iron and some oral iron preparations.
  • Calcium, tea and coffee around the doseThese can reduce nonheme iron absorption. Food interactions matter most when treating deficiency, but tolerability also matters.

References

  1. Burden RJ, Morton K, Richards T, Whyte GP, Pedlar CR. Impact of iron deficiency and iron supplementation on exercise capacity of young athletes in training: a systematic review and meta-analysis British Journal of Sports Medicine. 2015.Source
  2. NIH Office of Dietary Supplements. Iron - Health Professional Fact Sheet National Institutes of Health. 2026.Source
  3. Pengelly M, et al.. Iron deficiency, supplementation, and sports performance in female athletes: a systematic review Journal of Sport and Health Science. 2025.Source