Ferritin holds the buffer that can be called on when demand rises.
Visual field guide 02Blood + nutrition
Iron stores fall
before the tank
looks empty.
Iron deficiency is a balance problem: iron leaves or is needed faster than food and absorption can replace it. Anaemia is a later stage—not the definition.
Follow the iron ↘A practical, 6-minute visual guide
YOUR IRON RESERVEFerritin reflects stored iron
IRON IN−IRON OUT=STORES
THE SEQUENCEDeficiency can begin
Deficiency can begin
before anaemia.
Haemoglobin may stay in range while the stored reserve is already running down.
Ferritin falls first. Fatigue or reduced exercise tolerance can occur, but symptoms are not specific.
There is not enough available iron to make the usual amount of haemoglobin in red blood cells.
Possible cluesFatigueBreathlessnessPalpitationsHeadacheRestless legsPica
These symptoms have many causes. Blood tests are needed to know whether iron is involved.
THE LEAKY-BUCKET QUESTIONReplace iron—and find
Replace iron—and find
why it fell.
A supplement can refill the bucket. It cannot repair an ongoing leak by itself.
Iron is leaving
Heavy periods, bleeding from the stomach or bowel, blood donation, surgery, parasites, or repeated blood tests can drain iron faster than it is replaced.
More is needed
Pregnancy, growth in childhood or adolescence, and rebuilding red blood cells after blood loss all raise iron requirements.
Too little arrives
A low-iron or very restricted diet can contribute—especially when needs are high. Food alone may be too slow to correct established deficiency.
The gate is blocked
Coeliac disease, inflammatory bowel disease, H. pylori or atrophic gastritis, bariatric surgery, low stomach acid, and inflammation can reduce uptake or iron availability.
DO NOT MISS THE SOURCENew iron deficiency in an adult can be a sign of hidden bleeding.
Heavy menstrual bleeding is common, but stomach or bowel bleeding also needs consideration—especially in men, post-menopausal women, or anyone with gastrointestinal symptoms, weight loss, black stools or visible blood.
CONFIRM THE PATTERNOne number rarely tells
One number rarely tells
the whole story.
Results are interpreted together with symptoms, life stage, inflammation and the suspected cause.
Usually the most useful marker of stored iron. A low result strongly supports deficiency.
Shows haemoglobin, cell size and whether anaemia is present—but normal haemoglobin does not rule out early deficiency.
Helps show how much iron is available to tissues, especially when ferritin may be misleading.
Inflammation can raise ferritin even when iron is unavailable. CRP and clinical context help interpretation.
Ferritin is not a universal pass/fail line.
Cut-offs vary with age, pregnancy, inflammation, chronic disease and guideline. Treat the person and the pattern—not an isolated screenshot of a result.
REPLACEMENT ROUTESDifferent labels.
Different labels.
One useful comparison.
Look for elemental iron, tolerance, cost and objective response—not the biggest number on the bottle.
USUAL FIRST STEP
Sulfate, fumarate or gluconate
These familiar tablets all deliver ferrous iron. No oral form is clearly best for everyone; ferrous sulfate is usually the least expensive.
What differs
The amount of elemental iron—not the large salt weight printed on the front.
Typical trade-off
Effective and widely available, but nausea, constipation, pain or diarrhoea can limit use.
Useful adjustment
Once-daily at most; every-other-day dosing may be easier to tolerate for some people.
THE LABEL TRAP
Salt weight ≠ elemental iron
Ferrous fumarate is about 33% elemental iron by weight, sulfate about 20%, and gluconate about 12%. Product labels should state the elemental amount. Compare that number.
THE ABSORPTION GATEWhat can keep iron
What can keep iron
on the wrong side.
These effects matter most when stores are low or when a tablet is not working. Do not turn them into a needlessly restrictive diet.
GUTFeFeFe
→ABSORPTION GATE
→BLOOD
Tea + coffee
Polyphenols can bind non-heme iron. Move them away from an iron-rich meal or tablet when iron is low.
Calcium
A large calcium dose may compete with absorption. Take separate calcium and iron supplements at different times.
Phytate
Bran, whole grains, legumes, nuts and seeds contain phytate. These foods are still nutritious; soaking, sprouting, fermenting or pairing with vitamin C can help.
Low stomach acid
Antacids and acid-suppressing medicines can reduce absorption of non-heme iron. Do not stop a prescription without medical advice.
Inflammation
Hepcidin rises during inflammation and closes the iron-export gate, trapping iron in storage and reducing gut uptake.
Gut disease or surgery
Coeliac disease, inflammatory bowel disease, gastritis, H. pylori and bariatric surgery can impair uptake or create ongoing loss.
PRACTICAL TIMING
Improve absorption without making treatment impossible
Vitamin C improves non-heme iron absorption. If empty-stomach dosing causes symptoms, a small tolerated meal can be a reasonable trade-off.
More frequent or larger dosing can raise side effects and hepcidin; it is not automatically more effective.
Ask a pharmacist for exact spacing—especially with levothyroxine, some antibiotics, antacids or bisphosphonates.
A COMPLETE RESPONSERefill the reserve.
Refill the reserve.
Close the leak.
Use blood tests and context—not symptoms alone.
Look for loss, higher need, low intake, malabsorption or inflammation.
Choose an oral form and schedule you can sustain, or IV iron when indicated.
Confirm haemoglobin and stores are responding; investigate if they are not.
SEEK URGENT CARE
Chest pain, fainting, severe breathlessness, a racing heartbeat at rest, vomiting blood, black tarry stools, or heavy uncontrolled bleeding need prompt medical assessment.
SOURCESEvidence behind