Iron and anemia: which form gets absorbed, how to take it properly and why a normal hemoglobin can lie

Do you know the most common nutritional deficiency on the planet? Iron shortage. According to the WHO over 571 million women (aged 15-49) live with anemia. In Europe one in ten women of reproductive age faces this problem.

The reason is pure math. Women lose iron every month, which is why their daily need is 18 mg (for men it is 8 mg), and during pregnancy it reaches 27 mg.

Our body has an intelligent safety system: it stores reserve iron in the protein ferritin (in the liver, spleen and bone marrow). When the balance breaks, though, the organism empties these depots first. Hemoglobin, the value everyone looks at first, falls last, only when the tank is empty.

The period in between is called latent iron deficiency: a state in which your test results are "within range", but you have no energy at all.

In the pharmacy I come across this constantly. Recently a 34-year-old client of mine showed me her results: hemoglobin 126 g/L (excellent), but ferritin below range, barely 9 µg/L. She told me: "The doctor says my tests are fine, but I barely get out of bed and my hair is falling out." And she was right. Her blood count is within range, but her stores are empty. The diagnosis is the doctor's job, but your task is to know what exactly to test.

The classic complaints develop slowly and the body gets used to them: constant fatigue that sleep does not fix, pale skin and pale mucous membranes, breathlessness when climbing stairs that never used to be a problem, palpitations, headache, cold hands and feet. Nails turn brittle and split into layers, and with a more pronounced deficit they take the shape of a spoon (koilonychia: a condition in which the nail plate becomes thin, concave in the middle and with raised edges). Hair thins diffusely across the whole scalp, a mechanism I examine in detail in the article on hair loss.

There are also stranger signals that rarely get mentioned. Restless legs in the evening that will not let you fall asleep. An irresistible craving for ice: the urge to eat, chew or suck on ice, straight from the freezer or from iced drinks (the medical name is pagophagia: a symptom, not a disease of its own, and its treatment targets the root cause). Sores in the corners of the mouth that no balm can heal, which I also cover in the piece on cracked lips. Frequent colds: iron contributes to the normal function of the immune system. In children the picture can look like irritability and poor concentration.

The higher-risk groups are: women with heavy periods, the leading cause in reproductive age. Pregnant and breastfeeding women. People on plant-based diets, because iron from plants is absorbed several times more weakly than iron from meat. In athletes iron loss comes from the high physical loads, as the element is excreted intensively through sweating and through micro-traumas to the feet when running. Regular blood donors. Teenagers in rapid growth.

Ferritin is the marker of the stores. The reference ranges of most laboratories start around 15 µg/L, but complaints with normal hemoglobin are also observed at values below 30-40 µg/L, and the assessment is individual and belongs to the doctor. One catch few people know: ferritin rises with inflammation and infection, so a "normal" ferritin during a cold can hide a real deficiency. This is why CRP often gets added to the panel.

The complete blood count calls for additional tests (hemoglobin, hematocrit, MCV), sometimes transferrin saturation (a laboratory test that shows what percentage of the transport protein transferrin is occupied by iron ions), plus vitamin B12 and folic acid, because their shortage also causes anemia, but through a different mechanism. For those two I have separate articles: on vitamin B12 and on folic acid. Tests are ordered and interpreted by the doctor, and self-treatment with iron "blindly" is not a good idea, because the surplus gets stored in the organs.

Finding iron deficiency anemia in men or in women after menopause calls for immediate medical clarification. In these cases the leading question is not how to compensate the deficiency, but where the source of chronic blood loss is. Hidden bleeding from the gastrointestinal tract is the first diagnosis the doctor must exclude. Taking iron supplements on your own is dangerous, as it can mask the symptoms and critically delay the discovery of a serious disease.

The label often shows a large figure that is not the real amount of iron. The number that matters is "elemental iron". Ferrous sulfate contains about 20% elemental iron, fumarate about 33%, gluconate about 12%. In other words, 325 mg of ferrous sulfate provide about 65 mg of actual iron. The supplements in the pharmacy usually carry between 14 and 40 mg of elemental iron per dose.

The forms split into several groups. The classic salts (sulfate, fumarate, gluconate) have been studied for decades and are inexpensive. Their main drawback is that they most often provoke constipation, nausea and stomach discomfort. Chelated iron (ferrous bisglycinate): here the iron is "packed" between two molecules of the amino acid glycine. Thanks to this it travels a different metabolic route in the body, absorbs easily and spares the digestive system. Liposomal and sucrosomial iron: these modern forms use a protective fat (lipid) capsule that carries the iron intact through the acidic environment of the stomach, with high bioavailability and better tolerability. There is also heme iron (from hemoglobin): a natural form of animal origin. It is absorbed directly as a whole molecule and its effectiveness is not influenced by stomach acidity or by food intake.

All these forms are sold as food supplements and the claims approved in the EU apply to them: iron contributes to the normal formation of red blood cells and haemoglobin, and to the reduction of tiredness and fatigue. That, however, does not make a supplement a treatment: a diagnosed anemia is treated with medicinal products, in more severe cases with intravenous iron, and the scheme is set and monitored by a doctor.

The biggest mistake is taking iron with the morning coffee. Coffee, tea, milk and calcium supplements block iron absorption when taken together with it. The rule to follow: iron in the morning with water or juice, coffee and dairy products at least two hours later. Vitamin C acts in the opposite direction and improves absorption, so a glass of orange juice or a vitamin C tablet with the dose helps; there is a separate article on its doses and forms. Magnesium is also taken at a distance from iron, not together, as I note with the magnesium forms as well.

One key detail changed medical practice in recent years and it involves the hormone hepcidin. Every time you take a dose of iron, the body reacts by raising hepcidin, which temporarily blocks further absorption.

A randomized study from 2017, published in The Lancet Haematology, showed that in women with deficiency, taking iron every other day leads to higher overall absorption compared to daily intake. The study also found that splitting the daily dose between morning and evening brings no benefits. This "every other day" scheme is a convenient alternative in case of stomach discomfort, but any change in intake is always agreed with the treating physician.

Taking iron supplements has its specifics. First of all, watch for drug interactions. Medicines such as omeprazole (proton pump inhibitors) suppress iron absorption. On the other hand, iron itself blocks the action of levothyroxine (for the thyroid gland), which is why the two need an interval of at least 4 hours between them.

The side effects are well known in practice. Black stools are a normal occurrence and should not worry you: they are simply the residue of the unabsorbed mineral. Manifestations like constipation and nausea, however, can be unpleasant. If your stomach reacts sharply, consult a doctor about switching the product, or move to taking it with a little food as a reasonable compromise.

Keep in mind that your stomach will adjust within a few weeks, while refilling the iron stores takes about 3 months on average. The therapy is never stopped on your own, only after a follow-up test of ferritin and hemoglobin, ordered and read by a doctor.

Iron from food comes in two variants. Heme iron (meat, liver, fish) is absorbed at 15 to 35%, while the plant form from lentils, spinach, eggs and pumpkin seeds is absorbed at only 2 to 10%, and the phytates in grains and the polyphenols in tea lower it further. The dietitians' trick is the combination: lentils with red pepper, spinach with lemon. Cooking in a cast-iron pot adds a small amount. With a proven deficiency, though, food rarely manages to catch up on its own and is not enough.

In pregnancy the needs jump and the prevention with iron and folic acid is decided together with the doctor monitoring you, as I also write in the article on folic acid. In children the dosage is strictly at the pediatrician's judgment and per kilogram. And one warning I cannot skip: iron overdose is among the dangerous poisonings in small children, so the box of tablets is kept away from children's hands, like any medicine at home.

There are moments when a supplement is not the answer. Confirmed anemia, intolerance to oral forms, absorption compromised by gluten enteropathy or bariatric surgery, ongoing losses: in these cases the doctor moves to medicinal iron or intravenous schemes. Warning signs that call for an urgent rather than a planned visit: blood in the stool, tarry black stools without iron intake, unexplained weight loss, breathlessness at rest. And if you wonder how to read your own results or which form makes sense in your case, write to me in the Ask Didi chat: I answer personally and free of charge, for information purposes only, without placing diagnoses and without changing prescribed therapy.

This article was written by Donka Arabadzhova, Master of Pharmacy, and confirmed against the following sources: World Health Organization: anemia, prevalence and causes; NIH Office of Dietary Supplements: iron, forms, elemental content and absorption; StatPearls: iron deficiency anemia, diagnosis and treatment; NHS: symptoms, causes and reasons for a check-up in iron deficiency anemia; Stoffel et al., The Lancet Haematology 2017: daily versus alternate-day iron intake; Regulation (EU) No 432/2012: the approved health claims for iron.