Iron deficiency in athletes: why endurance athletes are most at risk

You train the same as last season, but the intervals feel heavier and your heart beats higher at the same speed. Before you doubt your fitness: this is exactly the picture where iron can be the culprit. Iron deficiency creeps in, and in endurance athletes it creeps in faster than in non-athletes.

My take: as an endurance athlete you want to know your ferritin, not your haemoglobin. Waiting for haemoglobin to drop means waiting until the deficiency has already cost you weeks of pace.

Why endurance athletes lose more iron

In endurance sport several loss routes stack up. The impact of running breaks down red blood cells slightly faster, you lose iron through sweat, and intense effort can mildly irritate the gut so you absorb less. On top of that sits a brief inflammatory response after hard training that temporarily blunts iron uptake.

None of these routes is dramatic on its own. Together, week after week, your iron balance tips negative without you noticing. That is why in endurance athletes it is not chance but a pattern.

There is a lesser known mechanism at play too. After intense effort a hormone briefly rises that blunts iron uptake in the gut and locks iron in storage. The body does this as a protective response to the inflammation of hard training, but the side effect is that just after your hardest sessions you absorb iron least well. An iron-rich, protein-rich meal right after training is then less effective than you would hope. So spread your iron-rich food across the day rather than planning it all around training.

Who is most at risk

The Voedingscentrum lists menstruating women and people who eat little or no meat as groups at higher risk of low iron. Combine that with high training volume and the odds stack.

Why a standard blood test misses it

For fatigue, the GP often tests only your haemoglobin. That makes sense for detecting anaemia, but it is too late for an athlete. Haemoglobin only drops once your iron stores are truly empty. By then you have already had a long phase where your stores fell and your performance dipped while haemoglobin still sat neatly inside the range.

Ferritin reflects those stores and drops earlier. Note: ferritin also rises with inflammation, so a normal value just after a heavy block can mislead. That is why you add transferrin saturation and, if needed, CRP for a fairer picture.

What to test instead

• Ferritin: your stores, the earliest clue.
• Transferrin saturation: how much iron is available for transport.
• Haemoglobin: to rule out anaemia.
• CRP: to spot a distorted ferritin.

Test fasted and on a calm day, not right after a race. Compare with your previous measurement; a downward trend is more informative than a single number.

The three stages of iron deficiency

Iron deficiency does not appear at once, but in steps. Understand that order and you also understand why you want to catch it early.

The gain is in stage one. Anyone who only tests at stage three has left months of performance on the table that a simple measurement could have prevented.

What to do with low iron

Start with your diet. The Voedingscentrum points to iron-rich foods such as red meat, wholegrains, pulses and green vegetables, and to the role of vitamin C in absorbing plant iron. The Gezondheidsraad states that a varied diet provides enough iron for most adults, but that some groups, such as menstruating women, fall short sooner. Supplements can help, but too much iron is not harmless, so you do not do it on a guess. Always discuss supplementation and dosing with a doctor.

A few practical points raise your absorption without pills. Combine plant iron with a source of vitamin C, such as vegetables or fruit with the meal. Drink coffee and tea between meals rather than with them, because compounds in them blunt iron uptake. And do not expect a miracle from one good week: building a store takes months, not days. So patience, and a repeat measurement after a few months, matters more than switching fast.

This article is part of our guide blood values for endurance athletes. If you feel tired without a clear cause, also read tired despite good training. Build your own iron panel via composing your own blood test. How iron deficiency leaves your red cells smaller and paler shows up in your MCH value. Prefer a ready-made test? Our complete blood count gives your haemoglobin, haematocrit and red indices in one test.

A blood test gives direction, not a final verdict. Every result at Enhanced is assessed by a BIG-registered doctor, so you know what a low ferritin means in your situation.