Wellness · Nutrition
Iron and fatigue, the most common missed cause.
Iron deficiency is the most common nutritional cause of tiredness — and often missed because ferritin sits at the bottom of a “normal” range.
Why trust this guide
- 01
Clinically reviewed
Written by our editorial team and reviewed by a registered UK clinician before publication.
- 02
Sourced from the guidelines
Grounded in BSG, NICE CKS and RCOG guidance — not opinion.
- 03
Practical, not preachy
Built for real UK patients who want to know what to test, what to take, and when it points to something bigger.
Key facts
Iron deficiency at a glance.
The essentials, in plain English — what it is, who it affects, what to test and how it is treated.
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What it is
Low iron stores — anaemia is the late stage, not the whole story.
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Common groups
Menstruating women, vegetarians, coeliac disease, older adults.
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Ferritin cut-offs
Below 30 µg/L is likely deficient; below 100 in someone symptomatic warrants treatment.
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Symptoms
Fatigue, hair loss, cold intolerance, restless legs, pica.
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Test
Ferritin plus full iron studies and FBC — request them together.
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Treatment
Dietary changes and iron supplementation — a course, not a snack.
Why this guide matters
One label — three very different problems.
“Low iron” hides a spectrum, and the fix depends on which end of it you are on. The three points below shape the rest of this page.
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It is not just anaemia
Symptoms start long before haemoglobin drops — ferritin is the earlier warning.
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A number, not a diagnosis
A low ferritin points to a cause — often heavy periods, coeliac or a slow bleed.
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Treatment is a course
Weeks of iron, not days — and a recheck to confirm it worked.
Testing and steps
From symptoms to a treated deficiency — step by step.
The path most patients take from a suspicious set of symptoms to a fully corrected iron store.
Phase 1 · Test and treat
Diagnose, address the obvious cause, start iron
Phase 2 · Follow-up
Dose sensibly and recheck the numbers
Phase 3 · Escalate
Look deeper or move to IV iron
- 01
Test and treat
Blood test — the full picture
Ferritin, iron, TIBC, transferrin saturation and FBC together — not ferritin alone.
- 02
Test and treat
Address obvious causes
Heavy periods, GI blood loss, coeliac screen — the cause matters as much as the number.
- 03
Test and treat
Dietary iron with vitamin C
Pair iron-rich foods with a vitamin-C source at the same meal.
- 04
Follow-up
Oral iron, every other day
Alternate-day dosing improves absorption and reduces side effects.
- 05
Follow-up
Recheck at 8–12 weeks
Ferritin and haemoglobin should be climbing — if not, look again.
- 06
Escalate
If no response — look further
Investigate absorption (coeliac) or an occult bleed.
- 07
Escalate
Consider IV iron if oral fails
Intolerance, malabsorption or ongoing loss can all point to IV iron.
Typical timeline: 8–12 weeks from first dose to a meaningful recheck.
Signs it affects you
What iron deficiency actually feels like.
Eight signals — a few of them together, especially with heavy periods or a low-meat diet, is worth a blood test.
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Persistent fatigue
Not fixed by a good night’s sleep or a weekend off.
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Hair thinning
Diffuse shedding, often noticed in the shower or on the brush.
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Cold intolerance
Cold hands and feet out of proportion to the room.
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Restless legs
An urge to move the legs at night, worse when tired.
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Pica (unusual cravings)
Craving ice, chalk or earth — a classic pointer to iron deficiency.
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Brain fog
Poor concentration and sluggish thinking that is not about workload.
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Heavy menstrual bleeding
The most common cause of iron deficiency in the UK — and often normalised.
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Red flag
Unexplained iron deficiency in post-menopausal women or men — investigate a GI cause urgently.
Treatment
What actually restores iron stores.
Food alone rarely does the job once stores are depleted — this is what a proper course looks like.
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Iron-rich meals
Red meat, pulses, dark leafy greens — the foundation, not the whole answer.
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Vitamin-C pairing
Orange juice, peppers or tomatoes at the same meal boost absorption.
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Oral iron every other day
Better absorption and fewer side effects than daily dosing.
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Ferrous fumarate or bisglycinate
Bisglycinate tends to be gentler on the gut — good if fumarate is a struggle.
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Recheck at 8–12 weeks
A blood test to confirm the numbers are moving — do not treat blind.
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Tranexamic acid for heavy periods
A GP option that reduces menstrual blood loss and iron drain.
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Coeliac screen
A simple blood test if deficiency is unexplained or does not respond.
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IV iron infusion
Considered when oral iron fails, is not tolerated, or loss is ongoing.
What this guide is based on
The evidence behind every claim on this page.
UK specialist and primary-care guidance — current at the time of last review.
Key references
The guidelines we relied on.
A quiet reminder
This guide is for information, not medical advice.
Your GP or a haematologist can tell you what your specific results mean and what to do about them.
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British Society of Gastroenterology. Guidelines on the management of iron deficiency anaemia.
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National Institute for Health and Care Excellence. Clinical Knowledge Summary — Anaemia, iron deficiency.
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Royal College of Obstetricians and Gynaecologists. Guideline on heavy menstrual bleeding.
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NHS. Iron deficiency anaemia — patient information.
Red flags
When iron deficiency needs more than a supplement.
Most iron deficiency is treatable in primary care. These are the situations that need a doctor’s eye, not a pharmacy shelf.
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Iron deficiency in men or post-menopausal women
Almost always warrants investigation for a GI cause.
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GI blood loss suspected
Dark stools, rectal bleeding or unexplained anaemia — do not wait.
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New deficiency + weight loss
Consider malignancy — needs urgent GP review.
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Coeliac symptoms
Bloating, diarrhoea, weight change — screen before treating blind.
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IBD flare
Iron loss and impaired absorption together — specialist input needed.
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Post-bariatric surgery
Altered anatomy affects iron absorption — long-term monitoring.
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Repeated failed oral iron
Adherence, absorption or ongoing loss — investigate rather than repeat.
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Pregnancy with severe anaemia
Needs prompt obstetric-led management.
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Athletes with recurrent deficiency
Look at diet, GI losses and haemolysis — do not just top up.
Living with it
A course to finish, not a habit to graze on.
Four ideas that decide whether iron stores actually recover — or whether you are back here in six months.
A quiet reminder
Feeling better is not the same as being replete.
Energy often returns weeks before iron stores fully refill — keep going and recheck the blood test.
- 01 Course
Treat it as a course, not a snack
Iron replacement runs for months after ferritin normalises — stopping early is the commonest reason it comes back.
- 02 Cause
Fix the cause, not just the number
Heavy periods, coeliac and GI bleeding are common causes — treat those and iron often looks after itself.
- 03 Timing
Take iron away from tea, coffee and calcium
They meaningfully reduce absorption — a gap of an hour or two is enough.
- 04 Recheck
Ferritin at 8–12 weeks, then again later
One good result is not the end — re-test to confirm stores have refilled.
Frequently asked
Everything we get asked about iron and fatigue.
Quick answers on ferritin cut-offs, dosing, side effects and when to worry.
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Is a normal ferritin enough to rule out iron deficiency?
No — ferritin can sit in the lower part of the “normal” range and still cause symptoms. Below 30 µg/L is likely deficient, and below 100 in a symptomatic patient often warrants a trial of treatment.
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Why alternate-day iron rather than daily?
Iron blocks its own absorption for around 24 hours by raising hepcidin. Alternate-day dosing gives higher total absorption and fewer gut side effects.
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How long does it take to feel better?
Energy often improves within 2–4 weeks, but full replenishment of iron stores takes 3–6 months of consistent treatment.
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Do I need to avoid tea and coffee?
Not entirely — but do not take them at the same time as your iron tablet or an iron-rich meal. A gap of an hour or two is enough.
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What if oral iron upsets my stomach?
Try alternate-day dosing, switch from fumarate to bisglycinate, or take with a small amount of food. If it still fails, ask about IV iron.
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When should iron deficiency worry a doctor?
In men and post-menopausal women, or with weight loss, GI symptoms or repeated failed treatment — these need investigation, not just another prescription.
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