Iron is a key part of your oxygen transport, and in endurance athletes that store runs down faster than many people think. While running you lose iron through sweat, through your gut and through the impact of each footstrike. Ferritin and haemoglobin can show part of that picture, though they do not prove a diagnosis.
Research among endurance athletes estimates that low ferritin is more common in female runners than in the average population. The exact percentage differs per study. But the direction is always the same: many kilometres can put your iron store under pressure.
My belief after hundreds of results: athletes only look at iron when their times have been off for weeks. By then the simplest clue is often months old. A blood value stays a tool, not a final verdict. You can find more context in our pillar on blood values for athletes.
Why is iron important for your endurance?
Iron sits in haemoglobin, the protein that carries oxygen through your blood. Without enough iron, less oxygen reaches your muscles. For an endurance athlete that can mean fatiguing sooner and tiring earlier. Your iron status can therefore affect how a long effort feels.
Oxygen is your fuel during endurance work. The more oxygen your muscles get, the longer you can hold a pace. Iron plays a central role in that.
Iron is not only in haemoglobin. It also sits in enzymes that help make energy inside your muscle cells. That is why a low store can be noticeable before your haemoglobin itself drops. That distinction comes back later.
How can endurance training lower your iron?
Endurance training can lower your iron in several ways. You lose small amounts through sweat and through your gut. With running, the repeated impact of your footstrike can damage red blood cells. After hard effort a protein that can briefly slow iron uptake sometimes rises too.
That last one, hepcidin, often peaks in the hours after a hard session. High hepcidin can temporarily reduce the uptake of iron from food. With many training days in a row, that may add up.
Footstrike haemolysis sounds more dramatic than it usually is. It is a small, gradual loss, mainly on hard surfaces and at high mileage. Read also how exercise shifts your values in exercise and your blood values.
What can ferritin and haemoglobin show in endurance athletes?
Ferritin says something about your iron store, haemoglobin about the oxygen transport itself. Together they give a first impression. Low ferritin can point to a small store, even if your haemoglobin is still normal. A doctor always looks at the whole picture, not one single number.
See ferritin as your savings account and haemoglobin as your daily spending. Your store can shrink while your daily balance still adds up.
The table below puts three commonly used values next to what they can suggest in endurance athletes and where you can have them measured. See it as a peg, not a diagnosis.
| Value | What it can suggest in endurance athletes | Where you have it measured |
|---|---|---|
| Ferritin | A low value can point to a small iron store, sometimes before your performance drops | At your GP or through a sport-focused blood test |
| Haemoglobin | A low value can go together with fatigue and breathlessness on exertion | Part of a blood count, often taken in the same tube |
| Transferrin saturation | Can help tell whether iron is available for red blood cell production | In addition to ferritin, in consultation with your GP |
If you want to know more about the whole iron puzzle, our explainer on spotting iron deficiency with a blood test helps. Which values make sense for you depends on your complaints and your training load.
What does low ferritin with normal haemoglobin mean?
This is the nuance many endurance athletes miss. Your ferritin can be low while your haemoglobin is still within range. Your store runs down before the oxygen transport visibly drops. Some athletes notice less resilience in that phase, though that link is not proven.
The body protects haemoglobin for as long as it can. That means a normal haemoglobin is no guarantee of a full iron store.
How low ferritin without anaemia translates into performance still differs per person. There is debate about the threshold at which it matters. So this is exactly the kind of thing to discuss with your GP or a sports doctor, not to act on yourself.
How do you best measure your iron as an endurance athlete?
A few practical points make your result more useful. Ferritin is an inflammation protein and can rise temporarily soon after a hard effort. A rest day before the draw therefore often gives a fairer picture. A morning appointment helps to compare measurements with each other.
Picture an appointment on a Monday morning after a quiet weekend. No race in your legs, no long run the day before. That way you avoid a temporary peak making your ferritin look higher than your store is.
Also mention which supplements you take, because iron pills can affect your values. A one-off measurement stays a snapshot. A doctor prefers to look at the pattern over time rather than one number.
When should you talk to your GP?
Some signals deserve attention sooner. Contact your GP if your fatigue lasts for weeks, your performance drops without a clear reason, or you have breathlessness, dizziness or palpitations. Do not take iron on your own, because too much iron can be undesirable.
That sounds cautious, but it is actually reassuring. This way treatable causes are not missed and you avoid unnecessary supplements. According to Thuisarts.nl, blood testing is sometimes useful, but not always needed.
A GP usually starts with your story: how long it has been going on, what has changed in your training, how you eat and recover. Blood comes after that, aimed at what fits your situation.
Frequently asked questions
How do I know if my iron is low because of the training?
You cannot read that from how you feel. Ferritin and haemoglobin can give an indication, but many factors play a part. Your GP can help work out whether your training load plays a role.
Does the risk differ between men and women?
Female endurance athletes on average have a higher risk of low iron, partly through menstrual blood loss. But men with high mileage can also have a low store. It stays individual.
Does an iron supplement help my endurance?
A supplement only helps with a proven deficiency, and then under guidance. Without one it adds little, and too much iron can actually be harmful. Always discuss this with your GP.
What I would suggest
Do not wait until your times have been off for months, but do not panic over one low value either. Look at ferritin and haemoglobin alongside your training, your recovery and your food. Blood is a tool within that, not a final verdict. Discuss your complaints and your result with your GP, especially if the fatigue persists. Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- RIVM. Iron and nutrition: figures and context. Accessed 2026.
- NHG guideline / Thuisarts.nl. Anaemia and iron deficiency. Dutch College of General Practitioners. Accessed 2026.
- Netherlands Nutrition Centre (Voedingscentrum). Iron in the diet. Accessed 2026.
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