The short version
- You can be iron deficient with a normal haemoglobin — ferritin is the test that shows it
- Heavy periods, pregnancy, a plant-based diet and gut conditions are common causes
- Symptoms include exhaustion, breathlessness on exertion, hair loss and restless legs
- Finding the cause matters as much as correcting the level, particularly after menopause
What low iron actually feels like
The classic picture is exhaustion that sleep does not fix. Alongside it people often notice breathlessness climbing stairs, a racing heart, poor concentration, hair shedding, brittle nails, headaches, restless legs at night, and feeling cold when nobody else is.
None of that is specific. It overlaps with thyroid disease, depression, sleep apnoea and simply being under-slept — which is why it is a blood test question rather than a guessing one.
Anaemia and deficiency are not the same thing
Your body stores iron, and it draws on those stores before your haemoglobin drops. That means you can feel thoroughly unwell with empty stores and a normal full blood count.
The test that shows this is ferritin, which reflects stored iron. A low ferritin confirms deficiency even when haemoglobin is normal. Ferritin can also be falsely raised by inflammation, so your GP interprets it alongside other markers rather than in isolation.
Who is most commonly affected
- Women with heavy periods — by far the most common cause in this age group
- Pregnant women, and women who have recently given birth
- People eating little or no red meat, particularly if iron-rich plant foods are limited
- Endurance athletes
- People with coeliac disease, inflammatory bowel disease, or on long-term reflux medication
- Regular blood donors
Why the cause matters
Correcting the number without asking why it dropped can mean missing the actual problem. In premenopausal women, heavy periods explain most cases — and heavy periods are themselves treatable rather than something to endure.
In men, and in women after menopause, unexplained iron deficiency is treated more seriously, because blood loss from the gut is a possible cause and needs excluding. Your GP will ask about bowel habit and may arrange further investigation.
Treatment, and why it takes patience
Treatment depends on the cause and how low the stores are. Dietary change alone is rarely enough to refill depleted stores — supplementation is usually needed, and it is taken for months rather than weeks, because the stores refill long after the symptoms improve.
Supplements vary in dose and tolerability, and taking more is not better — alternate-day dosing is often better absorbed than daily. Your GP will advise on what suits you, arrange follow-up blood tests, and discuss other options where tablets are not tolerated or absorption is the problem.
Book a standard appointment and say it is about tiredness, so blood tests can be arranged at the same visit. See pathology and blood tests.
Common questions
Yes. Iron stores deplete before haemoglobin falls, so you can have significant symptoms with a normal full blood count. Ferritin is the test that reveals it.
Symptoms often improve within weeks, but stores take months to refill. Treatment usually continues well after you feel well, with follow-up blood tests.
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