Iron Deficiency & Anaemia
The commonest nutritional deficiency in the world — and a finding that always has a cause
What it is
Iron deficiency means the body's iron stores are depleted. Iron deficiency ANAEMIA is the later stage, when stores have fallen far enough that the body can no longer make enough haemoglobin and the red cell count drops. The distinction matters clinically and is almost always lost in consumer health writing: you can be iron deficient — and symptomatic with it — while your haemoglobin is still entirely normal. Ferritin, not haemoglobin, is what identifies that state. It is the most common nutritional deficiency worldwide, and it is emphatically not the same thing as anaemia, which has many other causes.
Why it matters
Iron deficiency is genuinely worth finding and treating: it causes fatigue, breathlessness on exertion, poor concentration, hair shedding, restless legs, and reduced exercise capacity, and correcting it in a deficient person reliably improves those things. But the reason this page exists is the question that comes before the treatment. Adults do not become iron deficient without a reason — iron is lost through bleeding, not absorbed, or not eaten. In menstruating people the usual answer is heavy periods, which are treatable and chronically under-treated. In men and postmenopausal women there is no normal route of iron loss, and new iron deficiency anaemia in that group is investigated as gastrointestinal bleeding — including colorectal cancer — until proven otherwise. An iron supplement corrects the number while the cause continues. That is the single most important thing anyone can know about low iron, and it is the thing you will not be told by anyone selling it.
What BioSignal knows about treating this
What works for Iron Deficiency & Anaemia
BioSignal’s clinical summary, most important first.
- FIND THE CAUSE — iron deficiency is a finding, not a diagnosis. Adults do not lose iron for no reason, and correcting the number without finding the reason is the central mistake of self-treatment
- In men and postmenopausal women, investigate the gastrointestinal tract — there is no normal route of iron loss in this group, and guidelines worldwide treat new iron deficiency anaemia here as possible GI bleeding, including cancer, until proven otherwise
- In menstruating people, address heavy menstrual bleeding — it is the commonest cause, it is treatable, and it is routinely normalised by patients and clinicians alike
- Replace the iron, once deficiency is confirmed — oral iron salts are first-line, cheap and effective, and correction reliably improves fatigue and exercise capacity in people who are genuinely deficient
- Take it in a way that is actually absorbed: ALTERNATE-DAY dosing is better absorbed than daily dosing (daily iron raises hepcidin, which blunts absorption of the next dose), and vitamin C or a source of ascorbate taken with it improves uptake of non-haem iron
- Treat coeliac disease, inflammatory bowel disease, or other malabsorption if that is the cause — supplementation alone will not keep up with an untreated cause
- Intravenous iron where oral iron is not tolerated, not absorbed, or not fast enough — a clinician's decision, and a genuinely effective one
- Recheck ferritin after treatment, and keep going: stores take months to refill after haemoglobin has normalised, and stopping early is why deficiency so often recurs
Signal Records relevant to this condition
Interventions and contributing factors — some of these records describe a cause rather than a cure. The rating shown is BioSignal’s confidence in that Signal Record, not a claim about how well it treats this condition. Open any of them for the full evidence.
- Vitamin CHigh confidence
Does not prevent colds — one of the best-tested negatives in nutrition. Shortens them slightly, but only if you were already taking it. Megadoses are mostly excreted: absorption saturates around 200 mg/day. Genuinely useful for iron absorption, and genuinely essential — scurvy is still real.
- PsylliumHigh confidence
The best-evidenced intervention in the gut ecosystem: constipation, IBS, LDL, and glucose — cheap, boring, and genuinely effective.
- AlcoholHigh confidence
A Group 1 carcinogen with dose-dependent harms. The heart-protection belief does not survive the methods designed to test it. Cutting back helps, even without quitting.
New to this? Read these first
How this usually unfolds
- Recognize risk factors
- Get diagnosed
- Track key biomarkers
- Lifestyle first
- Evidence-based treatment
- Long-term monitoring
Who is at risk
- Heavy menstrual bleeding — the most common cause in menstruating people, and frequently normalised rather than treated
- Pregnancy, and the postpartum period — iron requirements roughly double
- Gastrointestinal blood loss: ulcers, colorectal cancer, angiodysplasia, inflammatory bowel disease, long-term NSAID or aspirin use
- Coeliac disease — a classic and commonly missed cause of malabsorption
- Bariatric surgery and other gastric surgery
- Long-term proton pump inhibitor use (stomach acid is needed to absorb dietary iron)
- Vegetarian and vegan diets — non-haem iron is absorbed far less efficiently than haem iron
- Endurance athletes, particularly female distance runners
- Blood donation, especially frequent donation
- Infants, young children, and adolescents during growth spurts
How it's diagnosed
The test that matters is FERRITIN, which reflects iron stores and falls first — long before haemoglobin does. A full blood count adds whether anaemia has yet developed and shows the characteristically small, pale red cells (low MCV, low MCH). Ferritin has one important trap that catches clinicians as well as patients: it is an acute-phase reactant, so infection, inflammation, obesity, liver disease and malignancy all RAISE it. A 'normal' ferritin in someone with active inflammation does not exclude iron deficiency, which is why ferritin is interpreted alongside CRP, and why transferrin saturation is used when the picture is muddied. Once deficiency is confirmed, the investigation is not finished — it has only started, because the cause has still to be found.
Key biomarkers
Lifestyle
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Frequently asked questions
Should I just take an iron supplement?
Not without being tested, and not without asking why. Two reasons. First, iron is not harmless: taking it when you are not deficient causes real gastrointestinal side effects, and in people with haemochromatosis — an inherited iron-overload disorder that is far from rare — routine supplementation is actively dangerous. Second, and more importantly, an adult does not become iron deficient for no reason. Supplementing corrects the blood count while the cause carries on, and that is how a treatable bleed, coeliac disease, or a bowel cancer goes undetected for a year while somebody feels a bit better. Get a ferritin test, and then find out why it is low.
Can I be iron deficient if my blood count is normal?
Yes, and this is the single most commonly missed thing in this area. Iron deficiency and anaemia are different stages. Your body draws down its iron STORES first; only when they are exhausted does haemoglobin start to fall. So you can have a completely normal full blood count and be genuinely, symptomatically iron deficient — tired, breathless on the stairs, foggy, shedding hair. Ferritin is the test that sees that state. If you have been told your blood count is normal and you still feel exhausted, ferritin is a reasonable thing to ask about specifically.
When is low iron a red flag?
When there is no normal reason for it. In a man of any age, or a woman past menopause, there is no routine route of iron loss — so new iron deficiency anaemia in that group is investigated as gastrointestinal bleeding, including colorectal cancer, until proven otherwise. That is not alarmism; it is standard practice in every major guideline, and endoscopic investigation is the recommended next step rather than a trial of supplements. Seek prompt assessment if low iron comes with blood in the stool or black stools, unintentional weight loss, a change in bowel habit, or abdominal pain. In menstruating people the usual cause is heavy periods — which is common, is not something to simply put up with, and is treatable.
Does vitamin C help iron absorption?
Yes, for non-haem (plant) iron, and it is one of the few supplement pairings with a real mechanism behind it: ascorbate keeps iron in the form the gut can take up. Taking your iron with orange juice, or with a meal containing vitamin C, measurably improves absorption. It is worth being clear about the size of this, though: vitamin C is an absorption aid, not a treatment. It does not correct a deficiency and it does not remove the need to find out why the iron is low.
Why does my iron supplement upset my stomach — and is there a better way to take it?
Nausea, constipation and dark stools are extremely common with oral iron, and they are the main reason people abandon treatment before their stores are refilled. There is good evidence for a better approach: ALTERNATE-DAY dosing is absorbed more efficiently than daily dosing. A dose of iron raises hepcidin, the hormone that blocks iron absorption, and it stays raised for about a day — so yesterday's tablet is part of why today's is poorly absorbed. Taking iron every other day gives more absorbed iron with fewer side effects. If oral iron still cannot be tolerated or is not working, intravenous iron is effective and is a reasonable conversation to have with a clinician.
Is all anaemia iron deficiency?
No, and treating it as though it were is a common and consequential error. B12 and folate deficiency cause anaemia through a different mechanism, and B12 deficiency in particular can cause irreversible neurological damage if it is missed and treated as though it were iron. Chronic kidney disease causes anaemia by reducing erythropoietin. Chronic inflammatory and autoimmune disease causes anaemia of chronic disease, in which iron is present but locked away — and in which giving more iron does not help. Thalassaemia and other inherited disorders produce small red cells that can look like iron deficiency and are not. This is exactly why anaemia is investigated rather than assumed.
I'm vegetarian or vegan — am I at higher risk?
At higher risk of deficiency, yes, though not inevitably deficient. Plant (non-haem) iron is absorbed far less efficiently than the haem iron in meat and fish, so intake has to be higher to achieve the same absorbed amount. The practical response is not to assume you are deficient and supplement — it is to get a ferritin test, which will tell you, and to pair plant iron with vitamin C and keep tea and coffee away from meals, which measurably improves what you do absorb.
Evidence summary
The evidence here is unusually solid, and it is solid in a direction that consumer health content rarely reports. Iron deficiency causes fatigue and reduced exercise capacity, and repletion in genuinely deficient people improves both — this is well established in randomized trials, including in iron-deficient women without anaemia, which is the group most likely to be told their blood count is 'normal'. Ferritin is the best single test of iron stores, with the well-characterised caveat that inflammation raises it and can mask deficiency. Alternate-day oral dosing produces greater fractional absorption than daily dosing, via hepcidin, and is supported by direct trial evidence. Ascorbate enhances non-haem iron absorption. What the evidence does NOT support is the practice on which most iron sales depend: supplementing iron in people who have not been shown to be deficient, which does not improve fatigue and carries real harm in those with iron overload. And no trial result anywhere alters the clinical rule that gives this page its purpose — in men and postmenopausal women, iron deficiency anaemia is a reason to investigate the gastrointestinal tract, not a reason to take a tablet.
References & sources
- British Society of Gastroenterology — guidelines for the management of iron deficiency anaemia
- NICE Clinical Knowledge Summaries — Anaemia (iron deficiency)
- British Society for Haematology — guideline on the laboratory diagnosis of iron deficiency
- WHO — guidance on ferritin concentrations for assessing iron status
- Randomized trials of alternate-day versus consecutive-day oral iron dosing and hepcidin response
Educational information — not medical advice
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