Iron Deficiency in Active Women: Risk Factors and Why Testing Matters

Iron deficiency is the most common nutritional deficiency worldwide, and anaemia affects a substantial share of women of reproductive age globally (World Health Organization). Among athletes, reported prevalence varies widely between studies and populations, and iron deficiency is consistently described as more common in female athletes than male athletes (Sim et al., 2019).

The reason this matters for training is that low iron degrades exactly the things training depends on: oxygen transport, oxygen storage in muscle, and mitochondrial energy production. The reason it is worth writing about carefully is that its symptoms are indistinguishable, from the inside, from ordinary training fatigue, poor sleep, or a stressful month.

So read this as education about risk and about what a proper assessment involves. Train and recover by the symptoms and performance you actually log, but do not diagnose yourself from a symptom list, and do not treat yourself from an article. Iron status is determined by a blood test, interpreted in context, and iron supplementation is a clinical decision with real risks when it is taken without one.

Why Active Women Are at Higher Risk

Three things stack up.

Menstrual Blood Loss

Iron is lost with menstrual blood, and the loss repeats every cycle. That makes recurring blood loss the single largest driver of higher iron requirements in premenopausal women. Heavier bleeding means more iron lost, which is one of several reasons that unusually heavy periods are worth raising with a clinician rather than tolerating.

Exercise-Related Losses and Absorption Effects

Sim and colleagues (2019) review the mechanisms studied in athletes: mechanical breakdown of red blood cells with repeated foot strike, small gastrointestinal losses with hard endurance work, losses in sweat, and, importantly, the effect of exercise on hepcidin. Hepcidin is the hormone that regulates iron absorption, it rises with the inflammatory response to intense exercise, and while it is elevated, absorption of dietary iron is reduced. That combination, higher losses plus periods of reduced absorption, is why hard-training people can drift downward even with a reasonable diet.

Dietary Patterns

Iron in food comes in two forms. Heme iron, from animal tissue, is absorbed considerably more efficiently than non-heme iron from plants, eggs, and dairy. Diets low in red meat, plant-based diets, and periods of restricted intake all reduce the amount of iron actually absorbed, independent of what the label says.

Symptoms Overlap With Everything Else

This is the honest core of the article. Iron deficiency can present as fatigue, worse endurance, breathlessness at intensities that used to feel manageable, slow recovery, poor concentration, or restless legs.

Every one of those also describes under-recovery, poor sleep, high life stress, insufficient energy intake, or an ordinary hard training block. A symptom list cannot separate them, which is precisely why the next step is a test rather than a supplement.

What Testing Actually Involves

Serum ferritin is the marker most used to assess iron stores, because it falls before haemoglobin does. That means a standard full blood count can look normal while iron stores are depleted, which is why "my bloods were fine" is not always the end of the conversation.

Two things make interpretation a clinical job rather than a lookup:

• Reference ranges and thresholds vary between laboratories and between guidelines, and thresholds proposed for athletes differ from those used to diagnose anaemia in the general population. There is no single number that means the same thing everywhere.
• Ferritin is an acute phase reactant, meaning it rises with inflammation and infection. A recent hard training block or an illness can push it up and mask depleted stores, which is one reason clinicians look at ferritin alongside other markers rather than in isolation.

If your training has flattened out and fatigue is persistent, the useful action is to see a clinician and ask whether iron studies are appropriate for you, rather than requesting a single number and interpreting it yourself. Bring context: your training load, your dietary pattern, how heavy your periods are, and any relevant history.

Food First, Without Prescribing

Improving the iron content of your diet is a reasonable thing to do whether or not you are deficient, and it carries none of the risk of self-supplementation.

Heme sources, absorbed more efficiently: red meat, dark poultry meat, shellfish, sardines and other oily fish, liver.

Non-heme sources: lentils and beans, tofu, spinach and other leafy greens, pumpkin seeds, fortified cereals.

Things that help absorption of non-heme iron: vitamin C in the same meal, such as citrus, peppers, tomatoes, or berries, and eating a small amount of animal protein alongside plant sources.

Things that reduce it: tea and coffee with meals, and calcium-rich foods eaten at the same time as your highest-iron meal. Separating them by an hour or so is a low-effort adjustment.

This is diet quality advice. It is not a treatment for a diagnosed deficiency, and it will not correct depleted stores on its own if you are genuinely deficient.

Why We Are Not Publishing Doses

You will find specific iron doses, timing strategies, and dosing schedules widely repeated in fitness content. We are deliberately not repeating them, for three reasons.

Iron supplementation without a demonstrated deficiency is not benign. Excess iron accumulates, gastrointestinal side effects are common, and some people carry conditions such as haemochromatosis in which supplementation is actively harmful. Iron also interacts with other medications and with the absorption of other nutrients. And the correct dose, form, schedule, and duration depend on how depleted your stores are and on why they are depleted, which is information only testing provides.

If a clinician establishes that you need iron, they will also tell you the dose, how to take it, and when to retest. That combination is the treatment. An article that hands you the middle piece without the other two is not helping.

When to Make the Appointment

Talk to a healthcare provider if:

• Fatigue or declining performance has persisted for weeks despite adequate sleep, food, and a sensible training load
• Your periods are heavy enough to be disruptive, or have become heavier
• You are breathless at efforts that were previously comfortable
• You follow a plant-based or restricted diet and have never had iron status checked
• You have been told before that your iron was low, and have not been rechecked since

Keep Reading

• Training during your period: symptom-led training decisions, including when bleeding needs a clinician
• Symptom tracking: the log that makes persistent fatigue legible
• Menstrual cycle and training: the full picture on cycle and training
• Science and evidence: the equations and references behind the numbers we publish

Sources

• Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. European Journal of Applied Physiology, 2019.
• World Health Organization. Anaemia fact sheet.
• National Institutes of Health, Office of Dietary Supplements. Iron: fact sheet for health professionals.
• American College of Obstetricians and Gynecologists. Heavy menstrual bleeding.
• Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023.