Iron for endurance athletes: why it matters and what to do

Why endurance athletes run low on iron

Training itself drains iron through several routes at once, and the early stages of depletion sap your performance long before a doctor would call it anaemia. Iron carries oxygen in your blood and muscles, so when it runs low, your engine loses power, you fatigue early, and no amount of extra training fixes it.

This is one of the most common and most missed issues in endurance sport. Here is who is at risk, how to spot it, and the important bit: why you should never just start taking iron on a hunch.

How training depletes iron

Several mechanisms chip away at your stores.

Foot-strike haemolysis. Every time your foot hits the ground, the impact destroys some red blood cells. Runners get this most, but it happens to a degree in other weight-bearing sport too.

Sweat and gut losses. You lose small amounts of iron in sweat, and hard training can cause minor gastrointestinal bleeding that adds up over time.

Hepcidin, the quiet culprit. Hard exercise triggers a hormone called hepcidin, which spikes for several hours afterwards and blocks your gut from absorbing iron. So the very training that depletes you also temporarily shuts the door on replacing it. That matters for how you time any iron you do take.

Menstrual losses. For women, monthly blood loss is a major ongoing drain on top of all the above.

Who is most at risk

Not everyone needs to worry equally. The high-risk groups are clear.

• Female athletes. Menstrual blood loss combined with training losses makes this the highest-risk group by a distance.

• Plant-based athletes. Iron from plants (non-haem iron) is far less well absorbed than the haem iron in meat and fish, roughly 20% versus up to 35%. Vegetarian and vegan athletes can absolutely get enough, but they have to be deliberate about it.

• High-volume runners. Foot-strike haemolysis stacks up with mileage.

• Athletes who have been chronically tired and flat despite good training and recovery.

The signs

Low iron creeps in. The classic flags: unexplained fatigue, struggling on efforts that used to feel fine, breathlessness, heavy legs, poor recovery, and sometimes pale skin, headaches or feeling cold. The frustrating thing is these overlap with overtraining and under-fuelling, which is exactly why you should not guess. The only way to know is a blood test.

Test, do not guess

This is the most important point in this whole piece. Do not start supplementing iron based on symptoms alone. Before you take any iron supplement, speak to your doctor. This is not a disclaimer for the sake of it. It is genuinely important.

Iron deficiency is diagnosed with a blood test, primarily ferritin, which reflects your stored iron, alongside a full blood count. Many sports physicians consider ferritin levels that a standard lab calls "normal" to still be too low for an endurance athlete, with practical targets often cited around 40-50ng/mL and above for performance, though there is debate about exact thresholds.

The reason to test rather than guess matters: iron overload is harmful. Taking iron you do not need can cause toxicity and gut problems, and excess iron is hard for the body to get rid of. A small number of people also have a genetic condition that makes them store too much. Blind supplementing is not a harmless "just in case." Get the test, get a professional opinion, then act on the result.

Food first

For most people, the best approach is to get iron from food and protect your absorption.

Haem iron (well absorbed)Non-haem iron (less absorbed)Red meatLentils, beans, chickpeasLiverTofu, tempehShellfish (mussels, clams)Spinach, kalePoultry, fishFortified cereals, oatsPumpkin seeds, dark chocolate

Two practical habits that genuinely help.

Pair non-haem iron with vitamin C. Lentils with peppers, beans with a squeeze of lemon, fortified cereal with orange juice. Vitamin C markedly boosts absorption of plant iron.

Mind the blockers. Tea, coffee and calcium-rich foods reduce iron absorption, so do not wash down your iron-rich meal with a strong brew.

If you do supplement

Only ever on the back of a blood test and with guidance from your doctor or a sports dietitian. Self-prescribing iron is not something to do based on symptoms or a feeling.

If supplementation is recommended, timing matters. Because hepcidin blocks absorption for hours after exercise, taking iron away from training, or in the morning before a session rather than straight after, can improve how much you actually absorb. Alternate-day dosing is also emerging as better tolerated and absorbed than daily dosing. Iron supplements commonly upset the gut, so dosing strategy is worth discussing with whoever is advising you.

FAQ

How often should I test? For at-risk athletes, once or twice a year is reasonable, and sooner if you are suddenly flat for no clear reason. Test when rested and not right after a hard block, as inflammation skews ferritin.

Can I fix low iron with diet alone? Mild cases, often yes, especially by improving absorption habits. Established deficiency usually needs supervised supplementation to top up, then food to maintain.

I am vegan. Am I doomed to low iron? Not at all. Plenty of strong plant-based endurance athletes maintain good iron. It just takes intent: regular iron-rich foods, vitamin C pairing, and periodic testing.

In M0VE we build your everyday eating around real, varied food, which is the foundation that keeps iron and everything else where it should be. But iron is one to take seriously. If you are tired and flat with no obvious reason, get a blood test before you reach for a supplement. Know your numbers, then act on them with professional guidance.