Iron (Fe) is an essential mineral involved in:
- Oxygen transport and storage through haemoglobin and myoglobin.
- Energy metabolism: chemical and biological processes that help cells meet their energy needs.
- Normal immune function
- Neurotransmitter synthesis
- And many other functions.
Preparing for events such as the Valencia Half Marathon makes adequate iron status important. When oxygen availability is reduced, the kidneys can increase production of erythropoietin, also known as EPO, which stimulates red blood cell production. Iron is needed to make haemoglobin, but one hard run does not instantly generate new red blood cells.
At altitude, oxygen’s partial pressure is lower, even though its percentage in air is similar. This can stimulate erythropoietin and red-cell production over time. Some athletes train at altitude to seek adaptations, but the performance response varies and requires adequate iron and suitable planning.
Red blood cells are produced in bone marrow and circulate for around several months before being removed, mainly by macrophages in the spleen and liver. Most of their iron is recycled for reuse. Smaller amounts are lost through normal shedding, sweating and bleeding.
How much iron is needed?
Serum iron is often reported in micrograms per decilitre (µg/dL), but a value below 55 µg/dL is not a universal diagnosis of deficiency. Interpretation requires the laboratory range and other markers.
The original article cites these daily intake reference values for Spain; they are examples, not personalised athlete prescriptions:
- 10 mg daily for men aged 20–59
- 18 mg daily for women aged 20–49
- 15 mg daily for adolescent girls
- 11 mg daily for adolescent boys
Both too little and too much iron can be harmful. Excess iron can contribute to oxidative damage, so do not take high-dose supplements without an indication.
Athletes may develop low iron status during intense training or high-load blocks. Contributing factors include inadequate intake, gastrointestinal or urinary losses, and menstrual bleeding. The main cause differs by person.
Low serum iron does not always mean anaemia. Anaemia is generally identified by a low haemoglobin concentration for the relevant population and circumstances, not simply a low red-cell count. Iron deficiency is one cause; vitamin B12 or folate deficiency and other conditions can also contribute. In endurance training, plasma-volume expansion can dilute measured concentrations, sometimes called sports pseudoanaemia.
A clinical assessment may therefore consider several markers, including:
- Serum iron
- Ferritin
- Haemoglobin
- Transferrin saturation
- Mean corpuscular volume
Anaemia can cause fatigue and poor concentration, but these symptoms have other causes too. The liver produces hepcidin, which regulates iron absorption and release from stores. It generally rises with higher stores or inflammation and falls when iron supply is low or red-cell production increases. This regulation does not guarantee that deficiency cannot occur.
Supporting iron absorption
It helps to distinguish two forms:
Haem iron: found mainly in animal tissues, including haemoglobin and myoglobin, and generally more readily absorbed.
Non-haem iron: found in plant foods and also some animal foods and fortified products. Its absorption is more affected by the meal’s composition.
The original estimate of roughly 10% absorption is only an approximation. Absorption varies with iron status, the form and amount of iron, other foods and physiological demands such as increased red-cell production at altitude.
To support absorption of non-haem iron, consider:
- Foods rich in vitamin C. Vitamin C helps keep iron soluble and reduces ferric iron to the more readily absorbed ferrous form, not the reverse as the source stated. After absorption and export into the blood, transferrin transports iron. Citrus fruit, peppers, tomatoes and broccoli are useful sources. Try lentil salad with broccoli and berries, or chickpea hummus with cumin and lemon.
- Protein foods containing lysine, histidine, cysteine and methionine. Specific amino acids and animal-tissue factors may affect iron availability, but they are not a replacement for treating deficiency.
- Foods providing vitamin A support normal health. Supplementing vitamin A alongside iron should be based on identified needs rather than used routinely.
- Copper also supports normal iron metabolism and red-cell formation.
Factors that can reduce absorption
Some meal components reduce absorption in single-meal studies. That does not mean nutritious foods containing them should be eliminated from a varied diet.
- Phytates: found in cereals, nuts and pulses. The source quotes a 10–50% reduction and examples using 50 mg or 150 mg vitamin C with an almost 30% improvement. These are context-dependent findings, not universal formulas for every meal.
- Oxalates: found in spinach, chard and cocoa. Their practical effect on iron status is less clear than a simple inhibitor list suggests.
- Polyphenols, including tannins: found in tea, coffee, wine and some fruit. Tea and coffee taken with meals can reduce non-haem iron absorption.
- Calcium-rich foods. Calcium can reduce iron absorption in some single-meal studies, but long-term effects are more complex. Routine separation of all calcium and iron foods is not necessary for everyone; follow specific advice when treating deficiency.
Practical recommendations
Learn what your body needs, eat a varied diet and look beyond marketing claims. An iron claim on a sweet pastry does not make it the best everyday source.
Requirements depend on age, menstruation, diet, training and health. If symptoms or risk factors suggest deficiency, arrange appropriate clinical assessment rather than supplementing blindly.
Iron deficiency remains common even where food is readily available. Causes can include inadequate intake, blood loss, impaired absorption and inflammation-related changes in hepcidin. Do not assume one mechanism explains every low result; investigate the cause.
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