Iron

Iron

This page is about iron as a dietary mineral — its role in the body, iron deficiency and food sources. For information on iron supplements — forms, doses and side effects — see iron supplements.

Iron is an essential trace mineral, and the most common nutritional deficiency in the world — the World Health Organization estimates that about a third of the world’s population suffers from it to some degree. Its main role is to form the core of hemoglobin, the protein in red blood cells that binds oxygen in the lungs and releases it in the tissues. About 70% of the body’s iron is found there.

But its role is much broader: it is a component of myoglobin (oxygen storage in muscle), of the respiratory chain enzymes in the mitochondria without which no ATP is produced, and of enzymes involved in producing neurotransmitters and in immune function. That is why iron deficiency causes fatigue even before full-blown anemia develops.

Two forms of iron — and the huge difference between them

This is the most important point for understanding iron in the diet.

Heme iron comes from animal sources — red meat, poultry, fish, as well as organ meats and products such as blood sausage, which is especially rich in it. It is packaged inside a porphyrin ring, absorbed through a dedicated receptor, and its absorption is 15%-35%. Just as important: its absorption is barely affected by inhibitors in the meal.

Non-heme iron comes from plant sources — legumes, tahini, tofu, leafy greens, fortified cereals. Its absorption is only 2%-20%, and it is dramatically affected by what sits beside it on the plate.

The practical meaning: looking at the number of milligrams on the label is not enough. 100 grams of spinach contains an impressive amount of iron on paper, but the body will absorb a fraction of what it would from a similar amount in meat. For this reason the recommendation for vegetarians and vegans is to consume 1.8 times the amount recommended for the general population.

What boosts and what blocks absorption

This table is the main practical tool in the article, and it applies almost only to non-heme iron:

Two rules of thumb that make a real difference: include a source of vitamin C with every iron-rich plant meal (lemon on your lentils, red pepper in your salad), and keep tea, coffee and calcium supplements an hour or two away from iron-rich meals.

Who is at risk of deficiency

• Women of reproductive age: monthly blood loss is the leading cause. The recommended intake for women is 18 mg a day compared with 8 mg for men — more than double.
• Pregnancy: the requirement rises to 27 mg because of increased blood volume and iron transfer to the fetus.
• Babies and toddlers: iron stores from birth run out around 6 months of age.
• Vegetarians and vegans: because they consume only non-heme iron.
• Endurance runners and athletes: hemolysis from the soles of the feet (“footstrike hemolysis”), losses in sweat, and inflammation that affects hepcidin.
• Regular blood donors and people with chronic bleeding in the digestive tract.

Symptoms of iron deficiency

Iron deficiency develops gradually, and the symptoms appear in stages. This is an important practical point: the first symptoms appear long before hemoglobin drops, so they are easy to miss or to put down to stress and lack of sleep.

Stage 1 — depleted stores (ferritin drops, hemoglobin normal):

• Persistent fatigue that doesn’t go away with sleep — the most common symptom, and usually the first
• Reduced fitness and shortness of breath on exertion that wasn’t there before
• Difficulty concentrating and brain fog
• Diffuse hair loss
• Sensitivity to cold, cold hands and feet

Stage 2 — the symptoms broaden:

• Pallor, especially noticeable in the conjunctiva (the inner surface of the lower eyelid), the gums and the nail beds
• Headaches and dizziness
• A racing heart, especially on exertion
• Brittle nails
• General weakness and exercise intolerance

Stage 3 — iron-deficiency anemia:

• All of the above, with increasing severity
• Shortness of breath even on light exertion
• Tachycardia, and in severe cases a heart murmur

Distinctive symptoms worth knowing — these are less well known, and when they appear they point to iron deficiency with high probability:

• Pica — an intense craving for non-food substances. The most common form is pagophagia — a compulsive urge to chew ice. This is a classic, recognized marker of iron deficiency, and it usually goes away within weeks of starting treatment.
• Restless legs syndrome (RLS) — an uncontrollable urge to move the legs at rest, especially at night. The link to iron deficiency is well established, and in this case the usual aim is a higher-than-usual ferritin.
• Koilonychia — flat or concave, spoon-shaped nails. A relatively late sign.
• Inflammation at the corners of the mouth (painful cracks at the edges of the lips) and a smooth, sore tongue.

A critical point: you can have all of these symptoms while your hemoglobin test is completely normal. This condition is called iron deficiency without anemia, and it is very common — especially in women of reproductive age. Hemoglobin is the measure that drops last; the stores empty long before it. So ask for ferritin explicitly, and don’t settle for a blood count.

How to read an iron test — ferritin, hemoglobin and the other markers

This is the part people get most confused about, so it is explained in detail here.

The trap worth knowing about: ferritin is also an inflammation protein. It behaves as an “acute phase reactant” and rises during infection, chronic inflammation, autoimmune disease, obesity and liver disease — completely independently of iron stores. The practical meaning: a person with inflammation may show a “normal” ferritin while their stores are actually empty. That is why CRP is usually tested at the same time, and when there is active inflammation, transferrin saturation is relied on as well, since it is not affected to the same degree.

A practical rule: ask your doctor for ferritin + blood count + CRP. Ferritin alone can mislead, and a blood count alone misses the early stage entirely.

And just as important — iron deficiency is a symptom, not a diagnosis. Finding a deficiency requires asking why. In a woman of reproductive age the cause is usually heavy periods, but in a man or a postmenopausal woman, iron deficiency requires investigation for hidden bleeding in the digestive tract — including ruling out malignancy. This is not needless alarm but accepted medical practice, and simply taking a supplement without finding the source is not enough.

Downsides and risks — when there is too much

This is the less familiar side, and it is no less important.

• Don’t supplement without testing — this is the critical point: the human body has no active mechanism for excreting excess iron. It regulates only absorption. Iron that accumulates, stays. Taking an iron supplement “just in case” or because of fatigue, without a blood test, is a dangerous practice.

• Hemochromatosis: a relatively common genetic disease (especially in people of Northern European descent) in which the body absorbs excess iron. Buildup in the liver, pancreas and heart causes cirrhosis, diabetes and cardiomyopathy. Iron supplements are dangerous for these patients.

• Oxidative stress: free iron catalyzes the formation of free radicals (the Fenton reaction). Excess iron is linked in the literature to oxidative damage to tissues.

• Supplement side effects: constipation, nausea, abdominal pain and black stools are very common and are a leading reason for stopping treatment. Taking it every other day was found in studies to increase total absorption (because of the regulation of the hormone hepcidin) and to reduce side effects compared with daily dosing. Full details on forms, doses and timing are on the iron supplements page.

• Iron poisoning in children: iron supplements are among the leading causes of fatal poisoning in young children. Store them out of their reach.

Iron-rich foods

Iron tables are almost always given per 100 grams, and that is misleading: nobody eats 100 grams of tahini or spirulina. The tables here also show a realistic serving.

Animal sources (heme iron — 15%-35% absorption):

Plant sources (non-heme iron — 2%-20% absorption):

Two notes that change how you read the tables:

1. The numbers don’t reflect absorption. 4.1 mg of heme iron from meat may contribute more to the body than 6.6 mg of non-heme iron from lentils. Mentally scale up the animal sources and scale down the plant ones.
2. Spinach is the classic misleading case. It appears on every list as an “iron source,” but its high oxalate content binds the iron and blocks most of it. Actual absorption from it is especially low — significantly lower than from legumes.

How to raise your iron levels — the practical plan

This is the most practical part of the page. The basic premise: in diagnosed deficiency, diet alone raises stores very slowly — over many months. A supplement under medical supervision is the fast tool; diet is what maintains the result. The two complement each other rather than compete.

1. Include vitamin C in every iron-rich plant meal. The single most significant step — it can double or even triple absorption. Lemon squeezed over lentils, red pepper in the salad, tomato alongside tahini. It needs to be in the same meal, not separately.

2. Keep tea, coffee and calcium away from mealtime. A cup of tea with a meal can reduce absorption by up to 60%. Separate them by an hour or two. The same rule applies to coffee, milk and calcium supplements.

3. Soak, sprout and ferment legumes and grains. These processes break down phytic acid and release bound iron. Soaking legumes overnight before cooking is a high-return habit.

4. The “meat factor.” Having meat in a meal also improves absorption of the plant iron alongside it. A small serving of meat with legumes is better than either one alone.

5. Cook in a cast-iron pot. A documented, real effect: cooking acidic, moist food — tomato sauce, for example — in a cast-iron pot significantly raises the iron content of the food. The longer and more acidic the cooking, the bigger the contribution. It is not a substitute for treatment, but it is a free extra.

6. Treat the cause, not just the symptom. If the source is heavy periods, digestive bleeding or undiagnosed celiac disease — without treating the cause, the stores will empty again.

What not to do: take an iron supplement on your own, without testing. See the downsides and risks section above.

Iron in pregnancy

The requirement in pregnancy rises to 27 mg a day — more than three times a man’s intake — for two reasons: the mother’s blood volume grows by about 40%-50%, and the fetus and placenta use iron themselves.

A point that confuses many people: some drop in hemoglobin during pregnancy is normal and physiological. Plasma volume grows faster than red blood cell mass, and the result is “dilution” — lower hemoglobin without a true deficiency. That is why the anemia threshold in pregnancy is lower (11 g/dL), and why here too ferritin is the more reliable marker.

Iron deficiency in pregnancy has been linked to preterm birth, low birth weight and marked maternal fatigue, so pregnancy is one of the few situations in which supplementation is routinely considered — but always under medical supervision and based on test results. First-trimester nausea and the constipation iron supplements cause are a common reason for stopping; taking them every other day or gentler forms may help, in coordination with your doctor.

Iron in vegetarian and vegan diets

The official recommendation for vegetarians and vegans is 1.8 times the recommended intake — that is, about 14 mg for a man and about 32 mg for a woman of reproductive age — because of the low absorption of non-heme iron.

What is important to know: most vegans are not anemic. Cohort studies find that iron intake on a vegan diet is usually higher than that of meat eaters — legumes, tahini and seeds are rich in it. What is found consistently is lower ferritin stores. In other words, the challenge is not the amount but absorption and stores.

So all the tools in the practical section above are seven times as relevant here: vitamin C at every meal, separating tea and coffee, soaking and sprouting, and periodic ferritin testing. Including vitamin C is in practice the difference between a plant-based diet that is sufficient and one that is not.

Summary

Iron is the most common nutritional deficiency in the world, and the key to understanding it lies not in the amount on the label but in the form and in what sits beside it on the plate: heme iron from animal sources is absorbed two to ten times better than plant iron, and absorption of plant iron changes dramatically depending on the presence of vitamin C on the one hand, and tea, coffee and calcium on the other.

For diagnosis, two points matter more than everything else: ferritin is the marker, not hemoglobin — you can suffer from fatigue, hair loss and shortness of breath with a completely normal blood count, and this is a very common situation; and ferritin rises with inflammation, so CRP should be tested at the same time so as not to miss a masked deficiency.

The opposite direction matters just as much: because the body has no way to get rid of excess iron, don’t take supplements without testing and a doctor’s approval. And finally — iron deficiency is a symptom, not a diagnosis: in a man or a postmenopausal woman it requires investigating the source of bleeding, not just supplementation.