How to fix iron deficiency properly
Iron deficiency affects around a third of the world. It is the single most common nutritional deficiency on the planet, and in women of reproductive age it is close to routine rather than rare. Yet it is one of the most under-tested and under-treated problems we see, and one of the most badly managed once it has been found.
Most people who come to us with low iron have already tried to fix it. They have bought a supplement, taken it for a few weeks, stopped, and assumed their body simply does not hold onto iron. In almost every case the problem is not the person. It is that nobody explained how iron absorption actually works, what to test, or how long correction really takes.
This article is the explanation.
Why iron matters more than most people realise
Iron is best known for carrying oxygen. Haemoglobin in your red blood cells needs iron to pick up oxygen in the lungs and drop it off in your tissues. Without enough iron, every cell in your body is working on a slightly reduced oxygen supply.
But oxygen transport is only part of the story. Iron is also required for
Myoglobin, which stores oxygen inside muscle
The electron transport chain, where your cells actually make energy
Dopamine and serotonin synthesis, which affects mood, focus and motivation
Thyroid peroxidase, the enzyme that makes thyroid hormone
Collagen production and wound healing
Immune cell function
Hair follicle cell division, which is one of the fastest dividing tissues in the body
This is why iron deficiency does not present as one clean symptom. It presents as a slow, general decline across several systems at once, which is exactly why it gets missed and put down to stress, age, motherhood or a busy job.
The signs of low iron
Energy. Fatigue that sleep does not fix. Waking up tired. Needing a nap or a coffee to get through the afternoon. Being wiped out by exercise that used to feel easy, and taking days rather than hours to recover.
Dizziness and lightheadedness. Standing up too fast and greying out. Feeling faint in hot rooms, on public transport or after a long gap without food. Palpitations, or a heart that seems to be working harder than the activity deserves.
Breathlessness. Getting out of breath on stairs, on hills, or during a normal conversation while walking.
Hair. Diffuse shedding across the whole scalp rather than a receding pattern. More hair in the shower drain, on the pillow and in the brush. A ponytail that has thinned. Hair that grows more slowly, breaks more easily and will not grow past a certain length. Iron deficiency is one of the most common reversible causes of hair loss in women, and it is repeatedly missed because haemoglobin comes back normal.
Skin. Pallor, particularly in the inner eyelids, gums and palms. Dull, dry skin. Dark circles under the eyes that look like tiredness but do not respond to sleep. Slower healing of cuts and spots. Cracks at the corners of the mouth. A sore, smooth or burning tongue.
Nails. Brittle nails that peel and split. Ridges. In more advanced deficiency, nails that flatten out and then curve upwards into a spoon shape.
Brain and mood. Poor concentration, word-finding difficulty, low motivation, low mood, anxiety, and the sensation of thinking through fog.
Other patterns worth knowing. Restless legs at night, an unpleasant urge to move the legs when you lie down. Feeling cold constantly, especially hands and feet. Headaches. Frequent infections. Craving and chewing ice, or craving non-food items such as chalk or soil, which is a genuine clinical sign called pica.
The blood tests you actually need
This is where most testing goes wrong. A standard blood count is not an iron test. You can have a completely normal full blood count and be significantly iron deficient. This state is called iron deficiency without anaemia, and it is the stage where most symptomatic people sit.
A proper iron assessment includes the following.
Ferritin. Your iron storage protein, and the single most useful marker. It falls first, long before haemoglobin does, so it is the earliest warning you will get. It is also the last to recover.
Serum iron. The iron circulating in your blood right now. It swings widely across the day and after meals or supplements, so it means very little on its own.
Transferrin and total iron binding capacity. Transferrin is the protein that carries iron around. When stores are low, the body makes more of it, so a high transferrin or high binding capacity supports a diagnosis of deficiency.
Transferrin saturation. The percentage of your carrying capacity that is actually filled. Below about 20 per cent suggests you do not have enough iron available for use. This is one of the most useful numbers on the panel and one of the most often omitted.
C-reactive protein. This is the test that changes everything. Ferritin is an acute phase reactant, which means it rises during inflammation, infection, obesity, liver disease and autoimmune conditions. Someone with an inflammatory condition can have a ferritin of 90 and still be iron deficient. Without a CRP alongside it, a ferritin result cannot be interpreted safely.
Full blood count. Haemoglobin tells you whether you have tipped into anaemia. Mean cell volume and mean cell haemoglobin tell you whether the red cells are small and pale, which is typical of iron deficiency. Red cell distribution width often rises early, before the other indices move.
Extras worth adding in the right person. Reticulocyte haemoglobin content shows how much iron is reaching new red cells over the last few days, which is a good early measure of response to treatment. Soluble transferrin receptor is unaffected by inflammation, which makes it valuable when CRP is high and ferritin is unreliable. B12 and folate should be checked alongside, since deficiencies commonly travel together and can mask each other on a blood count. Coeliac antibodies should be checked in anyone with unexplained iron deficiency.
Getting an accurate result
Test in the morning after an overnight fast where possible. Serum iron and transferrin saturation are strongly affected by recent supplements, so stop oral iron for at least five to seven days before testing or you will get a falsely reassuring picture. Avoid testing in the week after an infection, a vaccination or a hard endurance event, since inflammation will artificially lift ferritin.
What the numbers mean
There is an important difference between a result that is normal and a result that is optimal.
Many laboratory ranges start at around 10 or 15 micrograms per litre for ferritin. That lower boundary was set to identify the point at which bone marrow iron stores are completely empty, not the point at which people feel well. A large number of people are told their iron is normal at a ferritin of 18 while shedding hair and struggling to climb stairs.
The evidence supports higher targets for symptoms.
Below about 30, most clinicians treating symptomatic patients would consider this deficient even without anaemia
For hair loss, the literature broadly supports aiming for at least 50 to 70 before expecting regrowth
For restless legs, the evidence points to targets above 75 to 100
For endurance athletes, most sports medicine guidance sets a floor around 40 to 50
Numbers are guides, not verdicts. They must be read with your symptoms, your CRP, your saturation and your history.
How iron absorption actually works
Understanding this one mechanism explains almost every treatment failure.
Iron comes in two forms. Haem iron is found in red meat, liver, poultry and fish. It is absorbed through a dedicated pathway and around 15 to 35 per cent of it gets in. Non-haem iron is found in plants, pulses, fortified cereals and almost every supplement. Absorption is between 2 and 20 per cent depending on what else is in your gut at the time.
Absorption happens in a short stretch of the small intestine just past the stomach, called the duodenum. Non-haem iron must first be converted from ferric to ferrous form, which needs an acidic environment, then transported into the gut lining cell, then released into the bloodstream through a gate called ferroportin.
That gate is controlled by a hormone called hepcidin, made in the liver. Hepcidin is the master switch for iron.
When hepcidin is high, the gate closes, iron stays trapped in the gut cell, and is shed a few days later when that cell is replaced. You can swallow a large dose of iron and absorb almost none of it.
Three things raise hepcidin.
Inflammation. Any inflammatory state raises hepcidin as a defence mechanism, since bacteria need iron to grow. Obesity, autoimmune disease, inflammatory bowel disease, chronic infection, poorly controlled diabetes and even significant psychological stress can all keep the gate shut.
Adequate iron stores. This is normal and protective.
A recent dose of iron. This is the crucial one. A single dose of iron raises hepcidin for roughly 24 hours. Take iron again the next morning and you are absorbing into a closed gate.
That last point is why daily and twice-daily dosing, which is what most people are told to do, is often less effective than taking iron less often.
What helps iron absorption
Vitamin C. The strongest and best evidenced enhancer. It keeps iron in the absorbable ferrous form and can multiply non-haem absorption several times over. Around 100mg alongside the dose, or a glass of orange juice, or the supplement taken with a vitamin C tablet.
Meat, fish and poultry. These contain a factor that improves absorption of non-haem iron eaten in the same meal, quite separately from their own haem iron content.
An empty stomach and normal stomach acid. Iron is absorbed best when acid is available and the gut is otherwise empty.
Alternate day dosing. Research published in the last decade, including work in Blood and in The Lancet Haematology, showed that giving iron on alternate days rather than daily produced higher fractional absorption and better total iron uptake, with fewer side effects. Splitting a dose into twice daily performs worse than a single morning dose.
Fermented and sprouted foods. Fermentation and soaking break down phytates, which is why sourdough bread and soaked pulses deliver more available iron than their unprocessed equivalents.
What blocks iron absorption
Tea and coffee. Polyphenols and tannins bind iron in the gut and can cut absorption dramatically. A cup of tea with a meal can reduce non-haem iron absorption by more than half. Leave at least an hour on either side of an iron dose.
Calcium. The one mineral that interferes with both haem and non-haem iron. Milk, yoghurt, cheese and calcium supplements should be separated from iron by a couple of hours.
Phytates. Found in wholegrains, bran, nuts, seeds and legumes. Nutritionally excellent foods, but they bind iron in the gut.
Acid blocking medication. Proton pump inhibitors such as omeprazole and lansoprazole reduce stomach acid, and iron needs acid to be absorbed. Long term use is a common and overlooked cause of stubborn deficiency.
Stomach and gut conditions. Coeliac disease, inflammatory bowel disease, Helicobacter pylori infection, atrophic gastritis, previous gastric or bariatric surgery, and any condition affecting the duodenum will all limit absorption.
Zinc and other minerals in high doses. They compete for the same transport routes.
Eggs. Phosphoprotein in egg yolk binds iron. Worth knowing if your breakfast is eggs and coffee and you are wondering why your iron is not moving.
Why so many people are iron deficient
Menstrual loss. The dominant cause in women. Heavy periods, long periods, fibroids, adenomyosis and coils that increase bleeding all create a monthly deficit that a normal diet cannot replace. Many women have no idea their bleeding is heavy because they have nothing to compare it to.
Pregnancy and breastfeeding. Pregnancy alone requires roughly a gram of extra iron. Stores are often never rebuilt afterwards, and a second pregnancy starts from a lower baseline.
Plant based and low red meat diets. Not inevitable, but it takes deliberate planning. The iron is there, the absorption is the problem.
Endurance exercise. Runners, cyclists, triathletes and rowers lose iron through sweat, gut microbleeding and the destruction of red cells in the feet on impact. Exercise also raises hepcidin for several hours afterwards, which closes the absorption gate at exactly the time most athletes take their supplement.
Blood donation. A single donation removes around 200 to 250mg of iron, which takes months to replace.
Gastrointestinal bleeding. Ulcers, regular aspirin or anti-inflammatory use, diverticular disease, polyps and bowel cancer. In men of any age and in women past the menopause, unexplained iron deficiency should always prompt a conversation about investigating the gut, because iron deficiency can be the first sign of something that needs finding early.
Ageing. Stomach acid production falls with age, and with it iron absorption.
Why correcting it fails so often
Almost every failed iron correction we review comes down to one of the following.
Nobody found the cause. If you are losing more iron each month than you can absorb, no supplement will win that race. Treating the deficiency without treating heavy bleeding, a coeliac diagnosis or an ongoing gut problem is refilling a bath with the plug out.
Dosing too often. Daily or twice daily dosing keeps hepcidin high and absorption low, while doubling the side effects.
Taking it with the wrong things. Iron with breakfast tea, iron with a latte, iron with a calcium supplement, iron with a bowl of bran.
Side effects that were never troubleshot. Nausea, constipation and cramping cause most people to stop within a month. Changing the salt, the dose or the timing usually solves this. Very little of the standard tablet is absorbed, and the rest passing through the gut is what causes the symptoms.
Stopping far too early. Feeling better is not the same as being replete. Haemoglobin can recover in four to eight weeks while ferritin is still on the floor. Stopping at that point guarantees a relapse within months.
Untreated inflammation. If CRP is raised, oral iron will not work well no matter how perfectly it is taken. This is one of the clearest indications to change route entirely.
How to take iron so that it works
One dose, in the morning, on an empty stomach
Every other day rather than every day
With vitamin C or a glass of orange juice
No tea, coffee, milk or calcium for an hour either side
If it upsets your stomach, take it with a small amount of food and accept slightly lower absorption over stopping altogether
If a standard salt is not tolerated, gentler forms such as bisglycinate are worth trying
Different preparations contain very different amounts of elemental iron, which is the number that matters. Two products can look similar on the front of the box and deliver completely different doses.
How long it takes
This is the part almost nobody is told.
Symptoms often begin to improve within two to four weeks
Haemoglobin usually normalises in four to eight weeks
Ferritin takes three to six months, and longer if absorption is poor
Hair regrowth lags behind by three to six months, because the follicle has to re-enter its growth phase before anything visible happens
Treatment should continue for around three months after ferritin has reached target, not after symptoms have improved. Then retest.
When tablets are not enough
Intravenous iron is not a last resort and it is not exotic. It bypasses the gut entirely and corrects stores in one or two appointments rather than six months. It is the right choice when absorption is the problem rather than intake, and it is worth discussing if any of the following apply.
Oral iron has genuinely failed after a properly optimised trial
Side effects make oral iron impossible to continue
There is inflammatory bowel disease, coeliac disease or previous gut surgery
CRP is persistently raised
Ongoing losses outpace what the gut can absorb
Iron is needed quickly, such as before surgery or late in pregnancy
Can you have too much iron
Yes, and this matters. Iron is not a supplement to take on the assumption that more is better.
Haemochromatosis is a common inherited condition, particularly in people of northern European descent, where the body absorbs too much iron and deposits it in the liver, heart, pancreas and joints. It is one of the reasons a high ferritin should never be ignored either. Excess iron is linked to liver damage, diabetes, joint disease and heart problems.
The rule is simple. Test, treat to a target, retest, then stop. Do not supplement indefinitely without measurement, and do not supplement at all without knowing your baseline.
Common questions
Can I have low iron with a normal blood count. Yes, and this is the most common presentation we see. Ferritin falls months to years before haemoglobin does.
What is a good ferritin level. Above the laboratory minimum is not the same as optimal. For symptomatic people the working targets are considerably higher, and they depend on what you are treating.
Why do I still feel tired after taking iron for months. Usually because absorption is being blocked, the dose is being taken too often, the cause was never identified, or ferritin has not risen despite haemoglobin recovering. A repeat panel with CRP and transferrin saturation will normally show which.
Will iron regrow my hair. If iron deficiency is a contributor, correcting it properly can make a substantial difference, but expect a three to six month lag and be aware that hair shedding often has more than one cause.
Is it better to eat iron rich food or take a supplement. Diet maintains stores, it rarely rebuilds them. If you are already deficient you will almost certainly need a supplement or an infusion to correct it, then diet to hold it there.
How often should I test. If you have ever been deficient, at least annually. If you have heavy periods, are pregnant, donate blood, train seriously or follow a plant based diet, more often than that.
The point of all this
Iron deficiency is one of the few problems in medicine that is common, easy to detect, and fully correctable, yet it is routinely missed because the wrong test is ordered, the normal range is read too literally, and the treatment is given in a way that the biology does not allow to work.
If you have been tired for months, if your hair is shedding, if you are dizzy standing up, or if you have been told your iron is fine while feeling anything but, the answer is a proper iron panel read alongside your symptoms rather than a single number read in isolation.
speak to our experts here today.