Your ferritin value tells you how much iron you hold in reserve. Ferritin is the protein that stores iron, and that reserve ultimately determines how much oxygen reaches your muscles under load, because iron is the binding site in haemoglobin. A declining store therefore affects your endurance before anaemia appears. Endurance athletes also lose more iron than non-athletes, through sweat, through the gut and through red cell breakdown in the sole of the foot. At the same time a heavy training block lifts ferritin temporarily, which can make a deficit invisible. Measuring at the wrong moment therefore produces a reassuring number that is worth nothing.
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Source: Star-shl Reference population: Dutch primary-care population (Star-shl, Roche Cobas e801)
Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.
Check your own valueFerritin is the storage protein for iron, and the measured value, in micrograms per litre (µg/l), reflects the reserve your body draws on when it produces new red cells. Under heavy training that is the most interesting of all the iron values, because the store is the buffer a training block has to survive.
Iron sits at the centre of every haemoglobin molecule, binding the oxygen that travels to your muscles. As the reserve declines, production capacity falls first and the haemoglobin itself only much later. Your performance therefore drops while a standard blood count still looks normal, and that is exactly why ferritin yields more information in athletes than the blood count alone.
Star-shl uses 30 to 400 µg/l for men and 15 to 150 µg/l for women. That band describes the general population and no performance optimum. There is no scientifically established ferritin level above which you become faster, and that distinction matters: the lower end of the band is clinically relevant, while the upper end is nothing to aim at.
Always assess the result together with serum iron, transferrin saturation and CRP, the inflammation value. Because the assay differs between laboratories, the reference values on your own report take precedence.
A ferritin value after a heavy training week often tells you more about your inflammation than about your iron, because ferritin rises with inflammation and hard exertion is an inflammatory event. After a long run, a heavy strength session or a race, your CRP climbs and your ferritin is pulled up with it, and a measurement in that window can mask an empty store entirely. This is the most common error when assessing iron status around a training block, and the reason the result is always read alongside a CRP.
On top of that, endurance training actively inhibits iron uptake. Hard exertion raises hepcidin, the hormone that throttles iron absorption from the gut, peaking in the hours after exercise. Anyone training hard daily therefore spends a considerable share of the time in a state where iron enters less readily, precisely when the requirement is higher.
Losses are greater in athletes too. Iron is lost through sweat and through small bleeds in the gastrointestinal tract during intensive endurance work, and in runners there is also foot-strike haemolysis: red cells mechanically damaged in the sole of the foot with every landing. Each of these routes is small, but they run day after day.
The result is a pattern that is often missed. An athlete with an iron deficit presents with impaired recovery, a higher heart rate at the same load, less finishing speed and a sense of heavy legs, while the blood count and haemoglobin are entirely normal. The literature often counts an empty store from around 30 µg/l, well above the 15 µg/l used to establish anaemia, and the complaints you experience as loss of form sit exactly in that zone.
The reverse also holds: a higher value does not make you faster. Supplementing without a demonstrated deficiency improves no performance measure and accumulates iron, which the body cannot actively excrete.
Been ill? Wait a little
RequiredHad a fever, an infection or a vaccination in the past 2 weeks? Wait with the draw until you are fully recovered. These values react to inflammation and would give a distorted picture.
Preferably fasting
RecommendedComing fasting gives a slightly cleaner value, but it is not required. If it suits you, eat nothing from 22:00 the evening before and drink only water.
For an athlete, the timing of the draw determines whether the result is usable more than it does for anyone else. Do not measure within 48 to 72 hours of a hard endurance session, a race or an exhausting strength session: the acute-phase response lifts your ferritin and the number then describes your inflammatory status rather than your iron store. After a genuinely heavy effort such as a marathon, waiting several days to a week is wiser.
A rest day or an easy week is the best moment to measure. If you are mid-block, schedule the test at the start of a recovery day and always request a CRP alongside it. If that is raised, your ferritin cannot be interpreted and you repeat the measurement once it has normalised.
Sensible reasons to measure include unexplained loss of form, recovery that structurally takes longer than you are used to, a higher heart rate at a familiar load, or the start of a block in which volume rises sharply. A switch to plant-based eating is also a good reason, because the absorbability of the iron falls with it.
Preferably measure the whole iron panel at once: ferritin, serum iron, transferrin, transferrin saturation and CRP. Ferritin itself barely changes with a meal, but the laboratory lists the test as a fasted draw and serum iron fluctuates across the day, so follow the instruction that comes with your appointment and draw in the morning. If you repeat the measurement later in the season, keep the same time of day and the same position in the week.
With a declining iron store you notice something in your training first and in your blood count much later. The pattern is recognisable: recovery between sessions takes longer, your heart rate sits higher at a load you know well, the closing part of an effort feels heavier and your finishing speed drops. General complaints also occur, including persistent fatigue, breathlessness on exertion, dizziness, cold hands and feet, hair loss and restless legs.
Because these complaints also fit overtraining, under-recovery and low energy availability, the symptom pattern alone never identifies a cause. An iron deficit is, however, the simplest of those explanations to exclude, and the only one you can objectify with a single blood draw.
A raised ferritin rarely causes symptoms of its own in athletes, and the cause is usually not that you hold too much iron. The usual explanation is an acute-phase reaction after a heavy training period, an infection or an injury involving tissue damage, and alcohol use and fatty liver also lift the value. What you notice belongs in those cases to the underlying cause.
So do not read a high value after a heavy block as evidence of a well-filled store: it is more often an inflammatory signal than an iron signal, and it can conceal a deficit. Repeat the test in a quiet week, together with a CRP. If the value stays raised and transferrin saturation is raised as well, have a doctor assess it.
Low ferritin indicates depleted iron stores. Consider iron supplementation and dietary iron increase (red meat, spinach).
High ferritin may indicate inflammation, hemochromatosis, or liver disease. Consider CRP testing and comprehensive metabolic evaluation.
Low ferritin indicates depleted iron stores. Consider iron supplementation and dietary iron increase (red meat, spinach, fortified cereals).
High ferritin may indicate inflammation, hemochromatosis, or liver disease. Consider CRP testing and comprehensive metabolic evaluation.
The difference between the two forms of iron weighs more heavily at a high training load than for someone with modest turnover. Haem iron from meat, fish and poultry is absorbed considerably better than non-haem iron from pulses, wholegrain products, nuts and dark green leafy vegetables. Athletes eating plant-based therefore combine a higher requirement with a less absorbable source, and that is the group whose store declines fastest.
Use the timing of your meals. Hepcidin, which inhibits absorption, peaks in the hours after hard exertion, so an iron-rich meal is better placed away from that peak than directly on top of it. Take vitamin C with a plant-based iron source, because it clearly increases non-haem iron absorption, and keep coffee and tea out of that same meal: the tannins in them inhibit absorption, as does the calcium in a dairy-based protein shake.
Do not take iron on your own initiative, including in the run-up to a race. Supplementing without a demonstrated deficiency improves no performance measure, and the body cannot actively shed surplus iron. If a deficiency has been established, your doctor decides the approach, and if your ferritin stays low despite dietary adjustment, have the source of the loss investigated rather than raising the dose.
Iron forms the oxygen binding site in haemoglobin. As your store declines, the capacity to produce new red cells falls and your muscles receive less oxygen at the same effort. You notice this as a higher heart rate at a familiar load and less finishing speed, well before a standard blood count shows anything.
Indirectly, yes. Runners lose iron through sweat, through small gastrointestinal bleeds during long endurance efforts, and through foot-strike haemolysis, where red cells are damaged in the sole of the foot with every landing. Each route alone is small, but together and day after day they can noticeably erode the store during a build block.
Because ferritin is an acute-phase protein and hard exertion produces an inflammatory response. Your CRP climbs and ferritin rises with it, independently of how much iron you actually hold. A high value straight after a heavy block is therefore not evidence of a well-filled store and can in fact conceal a deficit.
In endurance athletes plasma volume increases, which makes haemoglobin look diluted without any iron being missing. That differs from a genuine iron deficiency. Ferritin helps separate the two: with dilution the store is normal, with a real deficit ferritin is low. Always assess both together.
Wait at least 48 to 72 hours after a hard effort, and after a marathon or comparable load preferably several days to a week. Always request a CRP alongside. If it is still raised, your ferritin describes the inflammatory response rather than your store, and the result carries no meaning for your iron status.
No ferritin level has been established above which you perform measurably better. The lower end of the reference band is clinically relevant; the upper end is no target. Correcting a deficiency can restore lost performance, but pushing beyond a normal store yields no demonstrable gain and accumulates iron the body cannot shed.
That is a decision for your doctor, based on the measured values rather than your training schedule. Supplementing iron without a demonstrated deficiency is harmful, and the right form and duration differ per person. With a low ferritin, also have the source of the loss investigated rather than simply refilling the store.
This marker is included in the following test panels.
Measure your ferritin, your iron store, key to endurance and energy. No referral needed.
A 5-biomarker inflammation panel inspired by InsideTracker's Inflammation category — hs-CRP, a complete blood count with differential, vitamin D and ferritin behind your inflammation score.
A 7-biomarker endurance panel inspired by InsideTracker's Endurance category — your complete blood count, full iron status, B12 and folate behind your endurance score.
Broad health panel: hormones, thyroid, vitamins, lipids, liver, kidney, and blood count.
Articles that explain this value in context.
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Ferritin
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