Anaemia and Iron Deficiency in Athletes

Iron is essential for haemoglobin and myoglobin and for the enzymes of aerobic energy production, so a shortage particularly affects endurance performance. The body stores iron as ferritin, and serum ferritin is the best routine marker of iron stores, with the important caveat that it also rises as an acute-phase reactant during inflammation, infection or after hard exercise. Absorption is controlled by the hormone hepcidin, which reduces iron uptake from the gut, and hepcidin rises with the inflammatory response to exercise, so a hard session can blunt iron absorption for several hours afterwards.

Athletes become iron deficient through several routes, and the most important are menstrual blood loss, particularly heavy menstrual bleeding, low energy availability and inadequate dietary intake, gastrointestinal (GI) blood loss and blood donation. Adolescent growth, altitude exposure and malabsorption such as coeliac disease also contribute, as does the higher iron turnover of heavy training, with foot-strike haemolysis and sweat losses probable but smaller contributors, since iron released by haemolysis is largely recycled. Vegetarian and vegan diets add risk because the non-haem iron in plant foods is less well absorbed.

Iron deficiency develops as a spectrum: stores fall first, giving a low ferritin with normal haemoglobin, and only later does frank iron deficiency anaemia appear.

The usual picture is non-specific: tiredness, a drop in training tolerance, slow recovery, breathlessness on exertion and underperforming despite good preparation. Iron deficiency without anaemia may contribute to fatigue and reduced endurance, particularly when stores are markedly depleted, but these symptoms are non-specific and other causes must be considered. Established anaemia may add pallor, a fast heart rate and light-headedness.

A focused history covers menstrual loss, diet and energy availability, blood donation, GI symptoms, use of non-steroidal anti-inflammatory drugs, previous gut surgery, and any family history of gut disease or a haemoglobinopathy, since iron deficiency is often multifactorial. Certain groups warrant a low threshold for testing: endurance, menstruating and adolescent athletes, those on vegetarian or vegan diets, those with relative energy deficiency in sport (RED-S), and anyone training at altitude. The skill is to avoid two opposite traps, neither dismissing a genuine problem as ordinary sports anaemia nor giving every athlete iron without asking whether the deficiency has an underlying cause.

A full blood count (FBC) shows the haemoglobin and the red cell indices. Iron deficiency anaemia is classically microcytic and hypochromic, but the mean cell volume (MCV) can be normal early, the mean cell haemoglobin often falls sooner, and microcytosis is not specific, so a thalassaemia trait or other haemoglobinopathy is considered where microcytosis is disproportionate to the anaemia or persists despite normal iron studies.

Ferritin is the key test of iron stores: in the absence of inflammation, a value below 15 micrograms per litre is highly specific for absent stores and below around 30 micrograms per litre generally indicates low stores, while a transferrin saturation below about 20 per cent supports iron restriction. Because ferritin rises with inflammation, it is read alongside a C-reactive protein (CRP) and, ideally, measured when the athlete is rested, in the morning, well hydrated and having avoided muscle-damaging exercise for a couple of days.

Where iron deficiency anaemia is confirmed, coeliac serology and urinalysis are checked, ongoing blood loss is reviewed, and upper and lower GI investigation is arranged for men and postmenopausal women, and for others where there are concerning features, whereas isolated low ferritin with normal haemoglobin is assessed individually rather than proceeding automatically to endoscopy. Dilutional pseudoanaemia is considered in a well endurance athlete with a small, stable fall in haemoglobin, normal iron status and no concerning symptoms, comparing with previous results and excluding other causes, and remembering that iron deficiency can coexist with it.

Good management starts with the cause, whether diet, heavy menstrual bleeding, low energy availability or a gastrointestinal source. Dietary advice covers iron-rich foods, the better absorption of haem iron from animal sources, vitamin C alongside plant-based iron in food, and correcting energy availability.

For established iron deficiency anaemia, usual first-line treatment is one daily tablet of a standard ferrous salt such as ferrous sulphate, fumarate or gluconate. Alternate-day single dosing may improve tolerability and the fraction absorbed, since a large dose raises hepcidin and blunts absorption of the next, and it suits athletes who tolerate daily iron poorly or an individualised plan. Iron is taken on an empty stomach or between meals, away from tea, coffee and calcium-rich food, and routine vitamin C tablets are not needed with therapeutic iron. Timing is arranged around training, avoiding the raised hepcidin of the hours after hard exercise rather than any blanket rule.

Haemoglobin is reviewed within two to four weeks, and a rise of at least 10 grams per litre over about two weeks suggests an adequate response, with iron continued for roughly three months after it normalises to rebuild stores; a poor response prompts review of adherence, continued blood loss, malabsorption, the diagnosis or coexisting vitamin B12 or folate deficiency. Iron deficiency without anaemia is treated when the athlete is symptomatic or at risk of progression, after addressing diet and cause, recognising that benefit is likeliest with markedly low ferritin and is not guaranteed, so ferritin and symptoms are monitored. Intravenous (IV) iron is reserved for when oral iron is contraindicated, ineffective or not tolerated, malabsorption is likely, or correction is urgent, delivered through an appropriate medical service and not as a performance shortcut in a non-deficient athlete.

On anti-doping, iron itself is permitted, but an intravenous infusion or injection totalling more than 100 millilitres in any 12-hour period is prohibited unless received during hospital treatment, surgery or a clinical diagnostic investigation, so IV iron outside those settings may need a Therapeutic Use Exemption (TUE) depending on the athlete's level. Emergency treatment is never withheld for anti-doping reasons, and blood manipulation and erythropoiesis-stimulating agents such as erythropoietin (EPO) are prohibited.

Prevention centres on the at-risk groups, endurance, female, adolescent and vegetarian or vegan athletes and those with low energy availability, through dietary optimisation, education and attention to energy availability, with periodic checks of iron status in these higher-risk athletes rather than screening everyone, at a frequency reflecting previous deficiency, menstrual loss, diet, training load and altitude plans.

Iron deficiency without anaemia does not normally require withdrawal from sport, though training load may need adjusting if fatigue or performance is significantly affected. An athlete with severe or symptomatic anaemia, or breathlessness, dizziness or chest symptoms at rest, should not train intensely and needs urgent assessment. Return to full training follows correction rather than coinciding with it, building over weeks to months as stores and red cell mass recover, and it is individualised, with no single ferritin or haemoglobin value that alone clears every athlete.

• •Current United Kingdom guidance on the diagnosis and management of iron deficiency anaemia, including when to investigate for an underlying cause and to screen for coeliac disease, underpins the general approach here.
• •Sport and exercise medicine consensus statements and reviews address iron deficiency in athletes, the significance of iron deficiency without anaemia, the role of hepcidin, and supplementation strategy.
• •Guidance on relative energy deficiency in sport links low energy availability to impaired iron status and wider health.
• •United Kingdom anti-doping guidance covers the intravenous infusion limit and the permitted use of iron.

• •Iron deficiency, with or without anaemia, is very common in athletes and can impair performance.
• •Iron deficiency without anaemia, a low ferritin with normal haemoglobin, can still cause fatigue and underperformance.
• •Ferritin is an acute-phase reactant and can read falsely normal with inflammation or after hard exercise.
• •Dilutional pseudoanaemia is a normal endurance adaptation and does not need iron treatment.
• •Newly diagnosed iron deficiency anaemia in a man or postmenopausal woman needs the cause found, including gut investigation.
• •First-line oral iron is a daily ferrous salt, with alternate-day dosing an option, and routine vitamin C tablets are not needed.