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The 60-second version
If you read nothing else
- The headline — iron deficiency and anaemia are not the same thing. You lose your iron stores first (that's deficiency); the haemoglobin drop (that's anaemia) comes much later. Treating only "anaemia" misses the earlier, fixable stage.
- Ferritin is the early-warning light — it reflects your iron savings. It falls first, often while the blood count still reads "normal". A normal haemoglobin does not rule out iron deficiency.
- It's massively under-diagnosed — iron deficiency without anaemia affects roughly 1 in 7 adults, and hits menstruating women, pregnancy and plant-based eaters hardest — yet is routinely waved through as "normal".1,2
- "Normal" ranges are set too low — symptoms are common at ferritin 15–30, and treating non-anaemic women with ferritin under 50 improves fatigue.1,3
- Iron needs a whole team — protein, stomach acid, a healthy gut, vitamin C, and cofactors (B12, folate, copper, vitamin A, zinc). It's rarely just "eat more red meat".
- Fix it properly — find the cause, use the right form and a smart schedule (often alternate-day dosing absorbs better), pair with vitamin C, keep it away from tea/coffee/dairy, and re-test.4,5
The core idea
Deficiency isn't anaemia
This is the single most useful idea in the guide. Iron runs down in stages, and the blood count is the LAST thing to change. Tap through the four stages to see what ferritin, haemoglobin and symptoms are doing at each one.
ↆ Click a stage to see what's happening
The number that moves first
Your ferritin
Ferritin is your iron savings account, and the first number to move. But it's read by ranges many experts say are set far too low — so a result can be flagged "normal" while you feel awful. And the numbers differ for women and men. Pick your sex and drag the slider to see where a value lands by optimum, not just "reference".
Why it matters
What iron does
Iron isn't only about "blood". It's a workhorse mineral your body uses everywhere — which is why running low shows up as such a wide, easily-dismissed spread of symptoms.
🫁 Carries oxygen
Iron sits at the heart of haemoglobin, ferrying oxygen from your lungs to every cell.
⚡ Makes energy
It's essential for producing energy inside cells (the mitochondria) — low iron literally leaves cells short of fuel.
🧬 Builds DNA
Iron supports DNA synthesis and cell division — needed wherever the body renews itself.
🛡️ Runs immunity
A working immune system depends on adequate iron to defend the body properly.
🦋 Supports hormones
Low iron blunts thyroid hormone production and can disrupt sex hormones and cycles.
🌡️ Holds temperature
Iron helps hold body temperature — feeling cold is a classic low-iron clue.
The machinery
How your blood is made
Red cells are made in the bone marrow, on demand, from raw materials in the blood. Two simple pictures explain most of it — the loop that drives production, and what haemoglobin is actually built from.
🔄 The oxygen loop that drives it
Your kidneys constantly sense oxygen. When it drops, they release erythropoietin (EPO) — a protein hormone — which tells the bone marrow to make more red cells. Those cells mature: stem cell → megaloblast → (needs B12 & folate) → reticulocyte → red blood cell, then head to the lungs to load oxygen.
Two things to keep: EPO is made by the kidneys — which is why kidney disease causes anaemia — and building red cells needs enough protein overall.
🧱 What haemoglobin is built from
A red cell is packed with haemoglobin = globin (a protein) + haem. Haem itself is built from iron + glycine (an amino acid) + succinic acid, and it's the part that actually binds oxygen.
So you need iron AND protein AND B-vitamins to build it — a shortfall in any one stalls the whole line, which is why anaemia is so often a nutrition story, not just an "iron" story.
Where it goes wrong
Why it runs low
Anaemia isn't one problem — it's any break in the chain from "enough oxygen in" to "enough raw materials to build a red cell". Four groups cover most of it, and one nutritional group is by far the most common and the most fixable.
🫁 Oxygen delivery (lungs/airways)
Low oxygen coming in, poor gas exchange, or a badly blocked nose / deviated septum means less oxygen reaching the blood — a driver of the whole loop. Good gas exchange also needs surfactant, a fatty film lining the lungs.
🫘 Kidneys
Kidney disease lowers EPO, so fewer red cells are made — and low overall protein leaves less material for EPO and haemoglobin.
🦴 Bone marrow
Where blood is actually made. It can be disrupted by some illnesses, by low vitamin D, and by systemic disease.
🩸 Blood-building supplies (the common one)
Not enough iron, not enough protein (including the amino acid glycine), low succinic acid, and low B-vitamins (B9/B12) all stall red-cell production. This nutritional group is by far the most common — and the most fixable.
Getting it in
Getting iron in
Eating iron and absorbing it are two different things. Absorption is fussy — it depends on the form of iron, your gut, and what else is on the plate. Expand each to see what helps and what blocks it.
Is this me?
Who's at risk & the symptoms
Iron deficiency isn't random — a few groups are much more likely to run low, and the symptoms are wide, vague, and often blamed on everything except iron. Crucially, many appear at Stage 1 — before any anaemia.
🎯 Most at risk
- Menstruating women — especially with heavy periods
- Pregnancy and the postpartum months
- Plant-based eaters (non-haem iron only)
- Endurance athletes and frequent blood donors
- Teenagers during growth spurts
- People with gut conditions (coeliac, IBD) or on acid-blockers
- Anyone with unexplained GI bleeding
🩺 What it feels like
- Persistent fatigue and breathlessness on exertion
- Hair thinning / loss; brittle, spoon-shaped nails
- Restless legs; palpitations; headaches
- Brain fog, poor concentration, low mood
- Feeling cold; reduced exercise tolerance
- A craving to chew ice (pica)
- Note: these can appear at Stage 1 — before any anaemia
Ask for the right bloods
What to test
A single haemoglobin is not an iron panel — it only catches the very last stage. To see deficiency early, you need the store (ferritin) plus a few numbers that help interpret it honestly.
| Test | What it tells you |
|---|---|
| Full blood count (FBC/CBC) | Haemoglobin and red-cell size (MCV). Falls last — a normal result does not rule out deficiency. |
| Ferritin | Your iron stores — the earliest number to drop. The single most useful iron test. |
| Total protein & albumin | The raw material for haemoglobin (globin) and for carrying iron — low protein undermines the whole build. |
| B12 (total/active) & folate (B9) | Needed to build red cells; a shortfall causes its own anaemia and often overlaps with iron deficiency. |
| Transferrin saturation & serum iron / TIBC | How much iron is actually in transit — often better than ferritin when inflammation is around. |
| CRP | Inflammation marker — needed to interpret ferritin, which is an acute-phase reactant that rises with inflammation. |
| Reticulocytes | Are new red cells actually being made? A quick read on whether the marrow is responding. |
Putting it right
Correcting it
Fixing iron well is more than swallowing a tablet. It means finding the cause, absorbing what you take, being patient, and re-testing to a real target — not just until the anaemia clears.
Shared practical basics
- Find and fix the cause — periods, gut bleeding, coeliac. Supplements alone won't fix ongoing loss.
- Food first — haem iron (meat, fish) plus vitamin-C-rich plants alongside non-haem iron.
- Supplement smartly — take with vitamin C, on an empty stomach if tolerated, away from tea/coffee/dairy.
- Consider alternate-day dosing — it often absorbs better and causes fewer gut side-effects, because a dose raises hepcidin and blocks absorption for ~24 h.4,5
- Re-test in ~8–12 weeks — ferritin and FBC. Keep going until stores are replete, not just until anaemia clears.8
The same facts get read two ways. Both are reasonable — they're answering slightly different questions. Here they are, side by side.
🩺 The conventional read
- Treats mainly when anaemia is present (low Hb), or ferritin is clearly low.
- Standard is oral iron salts (ferrous sulfate / fumarate / bisglycinate); IV iron for severe or intolerant cases.
- May not chase symptoms while the FBC still reads "normal", and is cautious about over-testing and over-treating.
- Rightly emphasises finding GI bleeding in the patients who need that work-up.
🌿 The functional / integrative read
- Treats symptomatic iron deficiency before anaemia, aiming for an optimal ferritin — not just above the floor.
- Reads a fuller panel (with CRP and transferrin saturation) and looks upstream — stomach acid, gut health, protein and cofactors.
- Prefers gentler, well-absorbed forms (e.g. bisglycinate) and re-tests to a target.
- Fair critique: optimal targets are partly consensus, ferritin is confounded by inflammation, and iron is genuinely harmful in excess — so test, don't guess, and don't take iron indefinitely without monitoring.
What to do
In practice
A tidy checklist
- Ask for ferritin, not just a blood count — with CRP to interpret it. A normal haemoglobin doesn't clear you.
- Read it by optimum (women ~30–100, men ~50–150 µg/L), not just "above the floor", and match it to your symptoms.
- Find the cause — heavy periods, gut issues, low protein, low stomach acid. Don't just top up and ignore why.
- Absorb it well — vitamin C with iron; away from tea/coffee/dairy; consider alternate-day dosing; be patient (weeks, not days).
- Re-test in ~8–12 weeks and continue until stores are full, not just until anaemia is gone — always with a clinician, because too much iron is harmful.
Keep reading — it's free
You've got the part that shows you where you stand. The rest is what to actually do about it — and I'll send it straight to your screen.
Still to come in this guide:
- Getting iron in
- Who's at risk & the symptoms
- What to test
- Correcting it
- In practice
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Go deeper
Sources
The evidence behind the numbers above. Superscript numbers in the text map to this list.
- Sex, lies, and iron deficiency: a call to change ferritin reference ranges — ASH Education 2023. Why "normal" ferritin ranges are argued to be set too low.
- Symptomatic iron deficiency without anaemia — an under-recognised phenomenon (ASH, Blood 2023). Deficiency symptoms before the blood count changes.
- Iron therapy improves fatigue in non-anaemic iron-deficient women — RCT. Treating ferritin under ~50 improves fatigue.
- Stoffel et al. — alternate-day oral iron increases fractional absorption. Why every-other-day dosing can absorb better.
- Moretti et al. — oral iron raises hepcidin and lowers later absorption (Blood 2015). The ~24-hour absorption block.
- WHO — serum ferritin concentrations for assessing iron status. Thresholds, and the effect of inflammation.
- Hurrell & Egli — iron bioavailability: enhancers and inhibitors (AJCN 2010). Vitamin C helps; phytate, tannins and calcium block.
- Alternate-day vs consecutive-day oral iron in iron-depleted women — RCT (eClinicalMedicine 2023). Dosing schedule and tolerance.