Iron deficiency is the most common nutritional deficiency in the world, according to the World Health Organization. In France, it affects around 25% of women of childbearing age and remains underdiagnosed in many adults. However, its consequences on quality of life are real and measurable: persistent fatigue, decline in cognitive performance, immune fragility, shortness of breath during exercise. Understanding the role of iron in the body, identifying populations at risk and knowing how to optimize their intake is a health prevention priority that this article suggests you put in your hands.
1. Iron in the body: a mineral with multiple roles
Iron is an essential trace element of which the adult body contains between 3 and 4 grams in total, distributed mainly between the blood (hemoglobin), muscles (myoglobin) and storage reserves (ferritin in the liver, spleen and bone marrow).
Its biological functions are fundamental:
- ●Oxygen transport: iron is the central component of hemoglobin, the protein in red blood cells that transports oxygen from the lungs to all organs and tissues. Without sufficient iron, this function is compromised and the entire body is in oxygen deficit.
- ●Energy production: iron is involved in the mitochondrial respiratory chain, the process by which cells produce ATP (cellular energy). A deficiency directly slows down energy production at the cellular level.
- ●Muscle functioning: myoglobin, a muscle protein rich in iron, stores oxygen in the muscles and releases it during exercise. Iron deficiency directly reduces physical performance.
- ●Immunity: iron is necessary for the proliferation and maturation of immune cells. A deficiency decreases the immune response and increases susceptibility to infections.
- ●Cognitive development and brain functions: iron is involved in the synthesis of neurotransmitters (dopamine, norepinephrine, serotonin) and in the myelination of nerve fibers. Its deficiency impacts concentration, memory and cognitive performance.
Type of iron Food sources Absorption rate Factors modulants Hemin iron Red meats, poultry, fish, seafood, offal (liver) 15 to 35% of the iron consumed Little influence by the other constituents of the meal. Stable and high absorption. Non-heme iron Legumes, whole grains, tofu, spinach, pumpkin seeds, dark chocolate, spirulina 2 to 10% of iron consumed Strongly influenced by other foods in the meal. Increased by vitamin C. Reduced by calcium, tea/coffee tannins, phytates.
2. Heminian iron vs non-Heminian iron: a crucial distinction
Not all iron-rich foods are created equal. The bioavailability of iron - that is to say the proportion actually absorbed by the intestine - varies considerably depending on its chemical form:
This difference in absorption explains why vegetarians and vegans are more exposed to iron deficiency even with high dietary intakes of plant iron. The dietary strategy to maximize non-heme iron absorption is therefore essential.
| Population | Daily requirement (ANC) | High requirement reason |
|---|---|---|
| Adult male (18-69 years) | 11 mg / day | Basal losses only |
| Adult female no menstruate | 11 mg / day | Basal losses only |
| Woman of childbearing age (menstruation) | 16 mg / day | Significant menstrual losses (1 to 2 mg/day additional) |
| Pregnant woman (2nd and 3rd trimester) | 25 to 30 mg / day | Expansion of blood volume, fetal growth, constitution of reserves infant |
| Adolescent (growth spurt) | 13 mg / day | Rapid growth + start of menstruation |
| Vegetarian | x 1.8 standard ANC | Non-heme iron only, worse absorb |
| Endurance athlete | Needs increased by 30% | Increased hemorheology, sweat loss, microtrauma |
3. Daily needs and populations at risk
Iron requirements vary considerably depending on profile. Here are the references established by ANSES:
| Aliment | Fer / 100 g | Type | Biodisponibilite |
|---|---|---|---|
| Boudin noir cuit | ~22 mg | Heminique | Très élevée |
| Foie de veau ou de boeuf | ~7 mg | Heminique | Élevée |
| Graines de courge (seches) | ~8 mg | Non heminique | Modérée (avec vit. C) |
| Spiruline seche | ~28 mg | Non heminique | Modérée |
| Lentilles cuites | ~3,3 mg | Non heminique | Modérée (avec vit. C) |
| Boeuf (steak) | ~2,5 mg | Heminique | Élevée |
| Tofu ferme | ~3 mg | Non heminique | Modérée (avec vit. C) |
| Epinards cuits | ~2,7 mg | Non heminique | Faible (phytates, oxalates) |
| Quinoa cuit | ~1,5 mg | Non heminique | Modérée (avec vit. C) |
| Chocolat noir 70%+ | ~11 mg | Non heminique | Faible sans combinaison |
Iron deficiency sets in gradually and its symptoms are often attributed to other causes (stress, overwork, poor sleep) before being correctly identified. There are three stages:
- ●Stage 1 - Depletion of reserves (low ferritin): ferritin reserves are depleted without hemoglobin being further affected. Often asymptomatic or with discreet fatigue. Detected only by a blood test.
- ●Stage 2 - Functional deficiency: the iron supply to the tissues becomes insufficient. Appearance of moderate fatigue, loss of concentration, lower tolerance to exercise, hair loss.
- ●Stage 3 - Iron deficiency anemia: hemoglobin falls below normal thresholds. Severe fatigue, shortness of breath at the slightest effort, palpitations, pale or earthy complexion, brittle nails, restless legs syndrome possible.
I consult my doctor if I have several of these symptoms. A simple blood test including CBC (hemogram) and ferritin dosage can confirm or rule out a deficiency and identify the cause. Ferritin is the earliest and most sensitive indicator of the state of iron reserves.
5. Optimize my iron intake through diet
Here is the ranking of the best food sources of iron, with the content per 100 g and the type of iron:
6. Strategies to maximize iron absorption
The amount of iron ingested is only part of the equation. The way I compose my meals considerably influences the proportion actually absorbed:
- ●Combine plant iron and vitamin C: this is the most effective strategy for increasing the absorption of non-heme iron. Vitamin C reduces ferric iron (Fe3+) to ferrous iron (Fe2+), which is much better absorbed. Practical examples: lentils with lemon juice, tofu with red pepper, spinach with strawberries, quinoa with tomatoes.
- ●Avoid tea and coffee during meals: the tannins in tea and coffee strongly inhibit the absorption of non-heme iron. I consume them at least 1 hour before or after the meal, never at the same time.
- ●Do not consume calcium at the same time as iron: calcium competes with iron for intestinal absorption. I do not combine dairy products and sources of iron in the same meal if I am trying to optimize my intake.
- ●Cooking in cast iron utensils: cooking in cast iron pots or pans modestly but really increases the iron content of prepared foods, particularly acidic foods (tomatoes, sauces).
- ●Soaking and sprouting legumes: soaking and sprouting reduce the content of phytates, antinutrients that inhibit the absorption of plant iron. I soak my lentils and chickpeas several hours before cooking.
💡 tips to remember
- Iron deficiency is the most common nutritional deficiency in the world. It affects 25% of women of childbearing age in France and often remains undiagnosed.
- Haem iron (meat, fish) is absorbed at 15-35%. Non-heme iron (vegetable) is only 2-10%: the way I compose my meal is as important as the quantity consumed.
- I systematically combine my vegetable iron sources with vitamin C: lentils + lemon, tofu + pepper, spinach + strawberries. This single reflex multiplies the absorption of non-heme iron.
- I drink my tea or coffee at least 1 hour after the meal: their tannins strongly inhibit the absorption of the iron consumed at the same time.
- I have my ferritin measured during my blood test: it is the earliest indicator of iron deficiency, well before the hemoglobin drops.
- Women of childbearing age have a requirement of 16 mg/day compared to 11 mg for men: a varied diet is rarely enough without particular attention to iron sources.
- In case of suspected deficiency: persistent fatigue, shortness of breath, pale complexion, hair loss hair - I consult my doctor for a complete blood test before any supplementation.
