Iron deficiency is one of the most common nutritional deficiencies worldwide and it is substantially more common in menstruating women. It is also routinely missed, because its main symptom is fatigue and fatigue gets attributed to everything else first.
Deficiency comes before anemia
The most important thing to understand is that iron deficiency and iron deficiency anemia are different stages, and symptoms often begin at the earlier one.
Iron stores deplete first. Hemoglobin holds steady for a while, drawing down reserves. Only when those reserves are exhausted does hemoglobin fall and anemia appear. This means a normal complete blood count does not rule out iron deficiency — a point that leads to a lot of people being told their bloodwork is fine while they still feel unwell.
The test that measures stores is ferritin. If fatigue is being investigated, it is worth asking whether ferritin was measured, not just hemoglobin.
One caveat on interpretation: ferritin rises during inflammation and infection, so a normal result in someone with an inflammatory condition can be misleading. Clinicians read it alongside other markers rather than in isolation.
Symptoms beyond tiredness
- Fatigue that sleep does not fix
- Breathlessness on exertion that is new for you
- Reduced exercise tolerance — the run that used to be easy
- Poor concentration and a sense of mental fog
- Hair shedding
- Brittle or spooned nails
- Restless legs, particularly at night
- Unusual cravings for ice or non-food substances
- Headaches, dizziness, cold hands and feet
- Pale skin, or pallor visible inside the lower eyelid
Restless legs and ice craving are worth flagging specifically. Both are strongly associated with low iron and both are frequently reported to clinicians without anyone connecting them.
Why it is common in women
The dominant reason is menstrual blood loss, and heavy periods in particular. Heavy menstrual bleeding is significantly underreported, partly because it is difficult to know what other people experience. Soaking through protection hourly, bleeding beyond seven days, passing large clots, or flooding overnight are all worth mentioning.
Pregnancy raises requirements substantially. Breastfeeding, frequent blood donation, endurance training, and diets low in bioavailable iron all contribute. Conditions affecting absorption — celiac disease, inflammatory bowel disease, previous gastric surgery, and long-term acid-suppressing medication — matter too.
Food, and its limits
Heme iron from meat, poultry and fish is absorbed far more efficiently than non-heme iron from plants. That does not make plant sources useless — lentils, beans, tofu, fortified cereals, pumpkin seeds and dark leafy greens all contribute — but absorption is more dependent on context.
Vitamin C markedly improves non-heme absorption, so pairing plant iron with citrus, peppers or tomato helps. Tea, coffee and calcium inhibit it, so separating them from iron-rich meals by an hour or two is worth doing.
Diet alone will maintain adequate stores. It will not reliably correct an established deficiency in a reasonable time, particularly when ongoing loss continues.
Treatment
Oral iron is the usual first step, and how it is taken affects both tolerance and absorption. Current evidence supports less frequent dosing than was traditionally recommended — every other day rather than multiple times daily improves absorption and reduces side effects. Nausea, constipation and dark stools are common; taking it with food reduces absorption but improves tolerance, which is often the right trade if it means you continue.
Repletion takes months, not weeks, and treatment should continue beyond the point where hemoglobin normalises in order to rebuild stores. Intravenous iron is available where oral is not tolerated, not absorbed, or where loss outpaces replacement.
What to ask for
If you have been persistently tired, ask specifically whether your ferritin was checked. Ask what the number was rather than whether it was normal — the threshold for symptoms is debated and sits above the level that defines anemia. And if your periods are heavy, say so plainly, because it is the most common cause and the one most often left unmentioned.
