Between 40 and 50% of elite female athletes present ferritin levels below the optimal performance threshold — without ever being officially “anemic.” Sifan Hassan, triple medallist at the 2024 Paris Olympic Games (gold in the marathon, bronze in the 5,000 m and 10,000 m), is a prime example of high-level iron management: her coach Tim Rowberry and she integrate a regular blood-monitoring program into their preparation, as documented in an interview with Athletics Illustrated in September 2024. Competing on the track and the marathon in the same Olympic season demands precise control of biomarkers — and ferritin is at the top of the list.
Definition: Iron Deficiency without Anemia (IDNA) refers to a state of iron depletion in which stores are insufficient to support optimal performance (ferritin < 30–50 ng/mL), without hemoglobin falling below clinical thresholds. It is the most common and most insidious stage of iron deficiency in female endurance athletes.
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Key Takeaways
- Low ferritin (< 40 ng/mL) costs −3 to 4% of VO2max in female athletes (Pyne et al., 2024).
- 3 distinct stages: low stores, IDNA, iron-deficiency anemia — only anemia is detected in routine medicine.
- Ferrous bisglycinate produces 64% fewer gastrointestinal side effects than ferrous sulfate (Fischer et al., 2023).
- Morning iron supplementation raises ferritin by +25.9 µg/L vs. +9.8 µg/L in the evening (McKay et al., 2023).
- Recommended ferritin target: 50–70 ng/mL for elite female athletes during the competition phase.
The 3 Stages of Iron Deficiency in Endurance Athletes
Iron deficiency is not just anemia. It progresses through three stages, of which only the last is routinely detected in a standard blood panel. Understanding these stages helps explain why so many athletes drag unexplained fatigue for months without a general practitioner raising any concern.
IDNA is the critical stage for elite athletes: it impairs neurotransmitter synthesis (dopamine, serotonin), disrupts the mitochondrial electron transport chain, and reduces recovery capacity, as confirmed by Borówka et al. (2026) in Quality in Sport (DOI: 10.12775/qs.2026.52.69538). The “brain fog” reported by many runners during intense preparation blocks often corresponds to this clinically invisible picture — neither hemoglobin nor hematocrit sounds the alarm.
−3 to 4% VO2max: The True Performance Cost of Low Ferritin for an Endurance Athlete
Three to four percent of VO2max may sound trivial. At elite level over 10,000 m, that translates to 30–45 seconds lost. Over a marathon, it means 3 to 5 minutes. For Sifan Hassan, whose margins over direct rivals in track finals are often measured in fractions of a second, such a drop would be decisive.
This is precisely what the systematic review by Pyne D.B., Pumpa K., Pengelly M. and Etxebarria N. (2024), published in the Journal of Sport and Health Science (DOI: 10.1016/j.jshs.2024.101009), quantifies. Covering 23 studies and 669 female athletes across 16 sports disciplines, it establishes that ferritin below 40 µg/L produces a measurable aerobic performance decline of 3 to 4% in athletes with VO2max > 45 mL/kg/min. Appropriate supplementation (100 mg elemental iron/day) yields an improvement of 2 to 20% depending on baseline deficit severity — a remarkable return on a simple nutritional intervention.
Cognitive performance is also affected. Iron deficiency disrupts myelin synthesis and reduces nerve conductance, manifesting as slowed tactical decision-making. For athletes competing across multiple disciplines in the same season — as Sifan Hassan did at Paris 2024, initially targeting four events before withdrawing from the 1,500 m — keeping ferritin above 50 ng/mL is not a luxury but a documented physiological necessity.
Foot-Strike Hemolysis and Hepcidin: The 2 Mechanisms Specific to Endurance Runners
Endurance athletes lose iron through two mechanisms not found in sedentary individuals: foot-strike hemolysis and the post-exercise hepcidin spike.
Foot-strike hemolysis is the mechanical destruction of red blood cells from the repeated impact of the foot against the ground. A PRISMA systematic review by Gartner A.M. et al. (2024), published in the Kansas Journal of Medicine (DOI: 10.17161/kjm.vol17.22673), documents a 16% increase in reticulocytes and a 21% drop in haptoglobin post-race in long-distance runners. Hemoglobin remains within normal range, masking this chronic iron depletion process — the very definition of a silent problem.
The hepcidin spike is the second mechanism. Intense exercise triggers interleukin-6 (IL-6) release, which stimulates hepatic hepcidin synthesis — the master regulator of iron homeostasis. This spike occurs 3 to 6 hours after training and can reduce intestinal iron absorption by approximately 36%, according to Borówka et al. (2026) in Quality in Sport (DOI: 10.12775/qs.2026.52.69538). An athlete taking iron supplements in the late afternoon absorbs a third less of their dose — a silent waste explaining why many supplementation protocols struggle to raise ferritin.
For a runner like Sifan Hassan, training at high frequency during intense preparation blocks, these two mechanisms compound each other: mechanical losses from hemolysis and reduced absorption from the hepcidin spike. This is precisely why regular blood monitoring — not annual testing — is essential for elite athletes competing across multiple race formats.
Which Form of Iron Should You Choose, and How Should You Take It?
The form: Ferrous bisglycinate (chelated iron) stands as the reference standard for athletes. The meta-analysis by Fischer J.A.J. et al. (2023), published in Nutrition Reviews (DOI: 10.1093/nutrit/nuac106), demonstrates that bisglycinate produces 64% fewer gastrointestinal side effects than standard ferrous sulfate (IRR 0.36, p < 0.01). The meta-analysis by Gallo Ruelas M. et al. (2024) in European Journal of Nutrition (DOI: 10.1007/s00394-024-03564-y) further shows that heme iron (meat, offal) causes 38% fewer side effects than non-heme iron. For vegetarians, read our article on vegetarian diet and endurance performance.
The timing: The randomized controlled trial by McKay A.K.A. et al. (2023), published in the European Journal of Sport Science (DOI: 10.1080/17461391.2023.2224285), is unambiguous: morning supplementation raised ferritin by +25.9 ± 10.5 µg/L versus only +9.8 µg/L for evening supplementation (p < 0.001). The practical rule: take iron in the morning, fasted or with a glass of orange juice (vitamin C potentiates absorption), before the post-training hepcidin spike takes effect.
Optimal hydration also supports intestinal iron absorption during supplementation. To replace sweat electrolyte losses during endurance training without added sugar, the Decathlon sugar-free lemon electrolyte tablets (40 × 4 g) provide sodium, potassium, and magnesium — ideal dissolved in 500 mL of water alongside your morning iron supplement.
Sugar-Free Electrolyte Effervescent Tablets — Lemon — 40 × 4 g (Decathlon)
Sugar-free electrolyte tablets providing sodium, potassium, and magnesium — essential to compensate sweat losses during endurance efforts, especially when iron supplementation is ongoing, as optimal hydration supports intestinal absorption. View electrolyte tablets on Decathlon. Product image: https://contents.mediadecathlon.com/p2521599/k$fb8db958836ab004914449de2b52afb4/picture.jpg?format=auto&f=400×400
For more on the synergy between minerals and recovery, see our article on magnesium bisglycinate for endurance athletes.
Should You Supplement with Iron Without a Prior Blood Test?
No. Iron supplementation without a blood test is not recommended for two reasons: the risk of iron overload (functional hemochromatosis, cellular oxidative stress) and the pointlessness of supplementing in the absence of a real deficit. Excess iron is pro-oxidant and can promote lipid peroxidation — a particularly damaging phenomenon for the mitochondria of endurance athletes.
The recommended minimum panel includes: serum ferritin, hemoglobin, hematocrit, transferrin saturation, and CRP (to rule out acute inflammation, which artificially elevates ferritin). A sports medicine physician can interpret these values in context: a ferritin of 25 ng/mL in a runner during an intensity block is very different from the same value in a sedentary individual.
The optimal target for elite female athletes is 50–70 ng/mL during the competition phase, according to the converging recommendations of recent literature. Below 30 ng/mL with symptoms (fatigue, performance decline, difficulty concentrating), supplementation is warranted. Between 30 and 50 ng/mL, targeted dietary optimization and quarterly monitoring are often sufficient.
Conclusion
Iron deficiency without anemia is the hidden Achilles heel of female endurance athletes: invisible on a standard blood count, yet devastatingly effective at sabotaging VO2max (−3 to 4%), recovery, and mental clarity. Sifan Hassan and her technical staff, by integrating regular blood monitoring into their preparation, apply exactly what the science has been documenting since 2023: foot-strike hemolysis, hepcidin spikes, supplementation timing — iron management is a discipline in its own right for performing across multiple formats in the same season.
The practical takeaways: bisglycinate in the morning, vitamin C as a co-factor, ferritin target 50–70 ng/mL, blood panel every 3 months during intense training. If you want to cross-reference your biological data with body composition and training load, Ograal offers personalized tracking — free access.
Frequently Asked Questions
What ferritin level should a female endurance athlete aim for?
The optimal target is 50–70 ng/mL during the competition phase. Below 40 ng/mL, Pyne et al. (2024, Journal of Sport and Health Science, DOI: 10.1016/j.jshs.2024.101009) document a VO2max decline of 3 to 4%. Quarterly blood testing is recommended during high-intensity training periods.
Bisglycinate or ferrous sulfate: which iron form causes fewer digestive issues?
Bisglycinate is the recommended form for athletes: 64% fewer gastrointestinal side effects than ferrous sulfate, according to Fischer et al. (2023, Nutrition Reviews, DOI: 10.1093/nutrit/nuac106). For exercise-sensitive digestive systems, it is the first-choice form.
Can foot-strike hemolysis genuinely deplete a runner’s iron stores?
Yes, chronically and insidiously. Gartner et al. (2024, Kansas Journal of Medicine, DOI: 10.17161/kjm.vol17.22673) document a 16% rise in reticulocytes and a 21% drop in haptoglobin post-race. Hemoglobin remains normal, masking the depletion. Trail runners and marathoners are most at risk.
Are vegetarian athletes at greater risk of iron deficiency?
Yes. Non-heme (plant-based) iron is absorbed 2 to 3 times less efficiently than heme iron (animal-based). Gallo Ruelas et al. (2024, European Journal of Nutrition, DOI: 10.1007/s00394-024-03564-y) confirm a clear advantage for heme iron. For vegetarians, maximizing vitamin C at meals and fermenting grains remain the primary levers.
Sources
- Pyne D.B., Pumpa K., Pengelly M., Etxebarria N. (2024). Iron deficiency, supplementation, and sports performance in female athletes: A systematic review. Journal of Sport and Health Science. DOI: 10.1016/j.jshs.2024.101009
- Fischer J.A.J., Cherian A.M., Bone J.N., Karakochuk C.D. (2023). The effects of oral ferrous bisglycinate supplementation on hemoglobin and ferritin concentrations in adults and children: a systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews. DOI: 10.1093/nutrit/nuac106
- Gartner A.M., Dombrowski N., Lowe N., Zackula R., Behzadpour V. (2024). Foot-strike Hemolysis: A Systematic Review of Long-Distance Runners. Kansas Journal of Medicine. DOI: 10.17161/kjm.vol17.22673
- Borówka K., Kądziołka W., Tymińska P., Frączek J., Kawka N., Górka P., Domagała S. (2026). Iron Deficiency and Beyond: Implications for Cognitive Function and Recovery in Female Endurance Athletes. Quality in Sport. DOI: 10.12775/qs.2026.52.69538
- McKay A.K.A., Attwell C., Dugan C., Nicholas J., Hopper L., Sim M., Peeling P. (2023). Timing is everything, but does it really matter? Impact of 8-weeks morning versus evening iron supplementation in ballet and contemporary dancers. European Journal of Sport Science. DOI: 10.1080/17461391.2023.2224285
- Gallo Ruelas M. et al. (2024). A comparative analysis of heme vs non-heme iron administration: a systematic review and meta-analysis of randomized controlled trials. European Journal of Nutrition. DOI: 10.1007/s00394-024-03564-y
- Hassan S. (2024). Interview post-Paris 2024 Olympics. Athletics Illustrated, September 2024. athleticsillustrated.com
