Iron for endurance athletes specifically

Iron deficiency is common in endurance athletes generally, and the combination of endurance training and a plant-based diet warrants active management rather than assumption.

Why athletes lose more iron

Several mechanisms, all documented.

Foot-strike haemolysis. Repeated impact destroys red blood cells in the feet. Relevant for runners in particular.

Gastrointestinal blood loss, which occurs in some endurance athletes, particularly during prolonged hard efforts.

Sweat losses, modest but real.

Haematuria, small amounts of blood in urine after hard efforts in some athletes.

Increased requirements for red cell production and for muscle myoglobin during training adaptation.

The hepcidin problem

The mechanism that is less well known and genuinely important for timing.

Exercise causes a transient inflammatory response, which raises hepcidin — a hormone that reduces iron absorption from the gut.

Hepcidin rises after exercise and peaks a few hours later.

The practical implication: iron absorption is reduced in the hours after training.

Which means iron-rich meals and iron supplements are better taken in the morning, or well away from hard sessions, rather than immediately after training when many athletes take them.

This is a genuinely useful piece of applied physiology that most athletes have never heard.

Testing

Do it. Do not assume, in either direction.

The relevant tests: full blood count, ferritin, and where interpretation is unclear, transferrin saturation and inflammatory markers.

Ferritin reflects stores and is the most useful single measure. It is also an acute phase reactant, which means it rises with inflammation — including after hard training — which can mask depleted stores.

Test when rested, not the day after a hard session.

The thresholds for athletes are debated. Some sports medicine practitioners use higher ferritin thresholds than the general clinical cutoffs for identifying athletes who may benefit from intervention, on the basis that performance may be affected before frank anaemia develops.

The evidence for treating low ferritin without anaemia is mixed, and there is reasonable evidence that correcting genuinely low stores improves performance in deficient athletes.

Test annually at minimum, and more often for female endurance athletes.

Who is at highest risk

Female endurance athletes, by a clear margin — menstrual losses plus training losses plus frequently restricted intake.

Athletes on plant-based diets.

Athletes in a deficit.

Adolescent athletes during growth.

Athletes training at altitude, where red cell production increases.

Runners particularly, because of impact.

The dietary management

Everything in our general iron article applies, with additional emphasis.

Vitamin C with iron-containing meals, which increases absorption substantially. This is the most effective single measure.

Tea and coffee away from meals, by at least an hour. Athletes who drink coffee with breakfast are undermining the iron in it.

Legumes, tofu, pumpkin seeds, fortified cereals as regular components.

Soaking, sprouting and fermenting where practical, to reduce phytate.

Cast iron cookware, which adds a modest amount, particularly with acidic foods.

Calcium supplements away from iron-rich meals.

Supplementation

Only on the basis of a test result and ideally with medical guidance.

Where indicated, some points that have emerged from recent research:

Alternate-day dosing has evidence for better fractional absorption than daily dosing, because a large dose raises hepcidin and blocks absorption for the following day.

It also causes fewer gastrointestinal side effects, which improves adherence.

Morning dosing, when hepcidin is lowest.

With vitamin C, and away from food where tolerated, though many people need food to avoid nausea.

Away from training, for the hepcidin reason.

Repletion takes months. Ferritin rises slowly and treatment should continue and be monitored rather than stopped as soon as haemoglobin normalises.

Why not to supplement without testing

Iron overload is harmful, and haemochromatosis — a genetic condition causing excessive absorption — affects a meaningful number of people who do not know they have it.

Excess iron also causes gastrointestinal side effects and may affect zinc absorption.

And unexplained iron deficiency sometimes has an underlying cause requiring investigation, which supplementation masks.

The symptoms to notice

Declining performance despite training. Unusual fatigue. Breathlessness at intensities that were previously comfortable. Poor recovery. Reduced motivation. Feeling cold.

These overlap almost entirely with the symptoms of under-fuelling, of overtraining and of inadequate sleep, which is precisely why testing rather than guessing is the useful step.

General information rather than individual advice. Do not take iron supplements without testing. Work with a sports dietitian and your doctor, and investigate unexplained iron deficiency rather than only supplementing it.