Can an iron deficiency be dangerous for your health? Explanations and solutions

Fatigue sets in, concentration falters, hair seems less dense than before, yet nights of sleep follow one another without bringing real recovery. Behind these daily signals lies, in many cases, an iron deficiency: the most widespread nutritional deficiency in the world, according to the World Health Organization (WHO), affecting nearly two billion people across all populations.

Paradoxically, iron deficiency in the body often goes unnoticed. Its manifestations are gradual, diffuse, and easily confused with the effects of stress or overwork. However, the consequences of uncorrected iron deficiency are very real: decreased energy and concentration, hair loss, weakened immunity, etc. Understanding why the body lacks iron, how to recognize the first signs, and, above all, how to effectively replenish its reserves are multiple topics discussed in this article.

Iron is an essential mineral that the body cannot produce on its own: it must be supplied through diet. An adult body contains between 3 and 5 grams in total, mainly in red blood cells, muscles, and in the liver where it is stored as ferritin. These quantities may seem modest, but iron plays a role in a very large number of vital functions, which explains why an iron deficiency can be dangerous and, if uncorrected, can have repercussions throughout the body.

The primary mission of iron is to transport oxygen throughout the body. It is at the heart of haemoglobin, the protein in red blood cells that captures oxygen in the lungs, carries it through the blood, and delivers it to every organ and muscle. When iron is deficient, cells are less well oxygenated, they produce less energy, and fatigue sets in; a deep fatigue that does not go away with rest.

Iron is also present in muscles, where it plays the same role on a smaller scale: storing a local oxygen reserve to support physical exertion. This is why an iron deficiency in the blood is also felt during exercise: faster shortness of breath, reduced endurance, difficult recovery.

Beyond physical energy, iron is involved in the production of certain chemical messengers in the brain (dopamine, noradrenaline) that regulate motivation, attention, and mood. An iron deficiency can therefore also lead to a decrease in mental vitality, irritability, or reduced stress resistance, even in people who do not feel particularly physically tired.

Not all iron-rich foods are equal. Depending on their origin, the iron they contain will not be absorbed in the same way by the body, and this is often where hidden risks of iron deficiency lie.

• Heme iron comes from animal products: red meat, offal, fish, seafood. This is the form best absorbed by the intestine, with an absorption rate of between 15% and 35%. An additional advantage: its absorption is little affected by the rest of the meal.
• Non-heme iron is found in plants: legumes, whole grains, green vegetables, nuts, and also eggs. Its absorption is much lower: between 2% and 20% depending on the context. It depends heavily on what is eaten at the same time: vitamin C significantly improves it, while tea, coffee, or dairy products reduce it. This reality explains why some people develop persistent iron deficiency despite a seemingly balanced diet.

Iron deficiency does not happen overnight. It develops in stages: first, reserves are depleted (low ferritin), then iron transport in the blood is reduced, and finally, iron deficiency anaemia occurs when red blood cells are no longer produced in sufficient quantities. At each stage, the body sends signals, some easy to spot but others much more subtle.

Persistent fatigue is the most characteristic sign of iron deficiency. This is not ordinary fatigue that a few good nights' sleep are enough to relieve: it settles in over time, resists rest, and is often accompanied by a general lack of energy. Shortness of breath on exertion, when climbing stairs or walking fast for example, is its direct physical consequence, caused by less efficient red blood cells in transporting oxygen.

Mentally, the link between iron deficiency and stress, difficulty concentrating, and irritability is well-documented. A meta-analysis published in Nutrients (2019) showed that low ferritin, even without declared anaemia, was associated with a measurable decrease in attention and cognitive performance. It is precisely this phase of hypoferritinaemia, meaning empty reserves but still normal haemoglobin, which most often goes unnoticed, while its effects on quality of life are already very real.

A severe iron deficiency is also visible on physical appearance. Hair is among the first to suffer, as hair follicles need a lot of energy and oxygen to function. When iron is deficient, the natural hair growth cycle is disrupted: hair falls out more, and regrows slower. A study published in the Journal of the American Academy of Dermatology (Trost et al., 2006) showed that low ferritin (less than 30 µg/L) was associated with an increased risk of hair loss in women. This hair loss is diffuse and gradual, often attributed to stress or seasonal changes, when it actually reflects an iron deficiency in the body.

On the nails, the first signs of a deficiency include fragility, ridges, and splitting nails. In more advanced cases, nails can become concave (spoon-shaped), a classic sign of severe iron deficiency. The skin may also appear pale, unusually dry, or dull.

Some signs of iron deficiency in the body are little known, but they deserve to be identified.

The tongue can become smooth and slightly painful, which is called atrophic glossitis, and the corners of the mouth can crack (what doctors call angular cheilitis). These manifestations affect mucous membranes and reflect a profound deficiency that has disrupted the normal renewal of epithelial cells.

Restless legs syndrome, which manifests as an irresistible urge to move the legs at night and disrupts sleep, is also significantly linked to low ferritin levels. A review published in Sleep Medicine Reviews showed that iron supplementation improves symptoms in affected patients with low ferritin.

Finally, the compulsive urge to chew ice or consume unusual substances, a behavior called pica, is a rare but characteristic warning sign of a severe, proven iron deficiency, which should lead to an immediate blood test.

Anyone can develop an iron deficiency, but some individuals are structurally more vulnerable, either because their needs are higher, or because their diet or lifestyle limits absorption. Identifying these profiles allows for anticipating the risks of iron deficiency before symptoms set in.

Women of childbearing age are the group most affected by low blood iron. Each menstrual cycle represents a regular loss of iron which, if not compensated by diet, gradually depletes reserves. In France, it is estimated that about one in four women of childbearing age have low ferritin, often without knowing it.

During pregnancy, iron requirements increase sharply: maternal red blood cell production accelerates, the placenta develops, and the baby also draws on maternal reserves. Recommended intake increases to 27 mg per day, compared to 16 mg outside of pregnancy. Monitoring ferritin levels throughout pregnancy is therefore essential. If you are pregnant or breastfeeding, it is important to seek advice from a healthcare professional before any iron supplementation.

Vegetarians and vegans consume exclusively non-heme iron, whose absorption is structurally more limited. Without targeted dietary strategies such as combining vitamin C, soaking legumes, or avoiding inhibitors at mealtimes, the risk of iron deficiency remains high, even with total intakes that seem correct on paper. For these profiles, a well-chosen iron supplement is often essential to maintain sufficient reserves.

Endurance athletes are also concerned, for cumulative reasons: a portion of red blood cells is mechanically destroyed with each stride (especially in runners), iron losses through sweat are real, and the intestine can bleed discreetly during intense exertion. In addition, a post-exercise hormonal phenomenon temporarily reduces the intestine's ability to absorb iron. Regular ferritin monitoring is recommended for this profile, even in the absence of apparent fatigue.

Several daily factors can reduce iron absorption unknowingly, and contribute over time to an iron deficiency in the body.

Phytates, present in whole grains, legumes, and seeds, bind to plant iron and prevent some of its absorption. Tannins in black tea, coffee, and red wine have a similar effect when consumed during or just after an iron-rich meal. Calcium, whether from dairy products or dietary supplements, competes with iron in the intestine.

Finally, anti-ulcer and anti-reflux medications (proton pump inhibitors) reduce stomach acidity, which is necessary for iron to be converted into an absorbable form by the intestine. Their prolonged use can contribute to a dangerous iron deficiency in the long term, even in people with a balanced diet.

Diet is the primary lever to meet iron needs and prevent iron deficiency. But you still need to know which sources to choose, how to prepare them, and which combinations to favor, or avoid.

Black pudding is by far the richest food in heme iron with approximately 22 mg per 100g. Offal (veal liver, chicken liver) follows with 7 to 10 mg per 100g, with a very good absorption rate. Red meat (beef, lamb) provides 2 to 4 mg per 100g. Seafood (oysters, clams, mussels) are also excellent sources, sometimes up to 12 mg per 100g depending on the species, with absorption comparable to that of meat.

Fish (sardine, tuna, mackerel) is an interesting alternative to diversify sources of heme iron, with good absorption and regular intake that effectively helps prevent iron deficiency in omnivorous individuals.

On the plant-based side, legumes (lentils, chickpeas, kidney beans), tofu, quinoa, and pumpkin seeds are among the most concentrated sources. Green leafy vegetables such as spinach, chard, or watercress usefully supplement intake, even if their absorption remains limited by the presence of oxalates.

To get the most out of them, a few simple habits make a real difference. Soaking legumes overnight before cooking reduces their phytate content and improves iron absorption. Germinating seeds and grains has a similar effect. Cooking degrades some iron-blocking compounds. These everyday actions do not require any particular effort and can significantly reduce the risk of iron deficiency in people on plant-based diets.

Vitamin C is the best ally of non-heme iron: it makes it more easily absorbable by the intestine and can double to quadruple the amount actually assimilated according to studies published in the American Journal of Clinical Nutrition. In concrete terms, this translates into a few simple actions: a squeeze of lemon juice on lentils, raw peppers in a quinoa tabbouleh, strawberries with tofu.

Conversely, avoiding tea, coffee, and dairy products within an hour of an iron-rich plant-based meal is a simple but effective precaution. These habits, without us being aware of them, can significantly reduce iron absorption and promote a gradual iron deficiency in the long term.

When diet is not enough to replenish reserves, particularly in cases of low ferritin confirmed by a blood test, severe iron deficiency, or anemia, iron supplementation becomes a serious option to consider. The chosen form, combinations, and duration of the routine are crucial for its effectiveness.

Digestive tolerance is the main obstacle to iron supplementation. The most common side effects of iron are nausea, constipation, abdominal pain, dark stools, and mainly concern classic forms based on high-dose ferrous sulfate, which release free iron into the digestive tract and can irritate it.

To limit side effects, there are better tolerated alternatives:

• Organic forms such as iron bisglycinate or iron gluconate are generally better tolerated by the intestine, with at least as effective absorption.
• Microencapsulated forms release iron gradually, avoiding concentration peaks that irritate the digestive mucosa. It is in this logic that Biocyte has developed its microencapsulated iron supplement, designed to combine absorption efficiency and digestive comfort.

Taking it on an empty stomach remains the most effective in terms of absorption, but in case of sensitivity, taking it with a light meal, avoiding milk, coffee, or calcium, is a valid compromise to ensure good regularity of intake.

As with food, vitamin C combined with iron supplementation improves its intestinal absorption. Its inclusion in the same formula, or simultaneous intake, is a well-validated practice.

Vitamin B9 (folic acid) and vitamin B12 play an important complementary role: they are necessary for the production of red blood cells and the maturation of blood cells. They are often included in formulas for pregnant women, vegans, or people with persistent fatigue of mixed origin. Their combination with iron makes it possible to simultaneously address several mechanisms involved in energy decline, for faster and more complete overall effectiveness.

Iron supplementation is not measured in weeks: replenishing depleted reserves takes time. As a general rule, it takes 3 to 6 months to normalize ferritin in cases of isolated low ferritin, and sometimes longer when anemia is declared or when the underlying cause (heavy periods, malabsorption) is not corrected. Hemoglobin, on the other hand, returns to normal more quickly, between 4 to 8 weeks, but deep reserves take more time.

Recommended monitoring includes: ferritin, hemoglobin, and, if necessary, red blood cell volume and transferrin saturation rate. These analyses allow verifying that the supplementation is effective and avoiding an excess of iron, which is not without health risks. Supplementation conducted without prior assessment is not recommended.

Iron is one of the few minerals for which the body does not have an efficient elimination mechanism. Taking iron without knowing your actual level exposes you to a risk of accumulation, which can damage the liver, heart, and joints.

A blood test makes it possible to evaluate two distinct markers: ferritin, which reflects storage reserves, and hemoglobin, which indicates whether oxygen transport is already compromised. These two values do not decrease at the same time; ferritin drops first, sometimes several months before hemoglobin is affected. Without this test, it is impossible to know what stage you are at, or what dose is actually necessary.

A doctor or pharmacist can also help identify the cause of the deficiency, such as heavy periods, malabsorption, a digestive pathology, etc.

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• Trotti, L.M. & Becker, L.A. (2019). Iron for the treatment of restless legs syndrome. Cochrane Database of Systematic Reviews.
• Hallberg, L. & Hulthén, L. (2000). Prediction of dietary iron absorption. American Journal of Clinical Nutrition, 71(5), 1147–1160.
• Trost, L.B. et al. (2006). The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. Journal of the American Academy of Dermatology, 54(5), 824–844.
• Anses. (2023). Table de composition nutritionnelle des aliments CIQUAL. Agence nationale de sécurité sanitaire de l'alimentation.