Iron

What can be said about iron, and what must be kept silent?

Let's start with the limit, because it dictates everything else. Iron is the only nutrient in this catalog for which we state that it should not be supplemented without medical advice. The body can absorb iron but has no active elimination pathway: what enters stays, and prolonged excessive intake accumulates in the liver, heart, and pancreas, where it becomes toxic. Conversely, a real deficiency is identified through a blood test—ferritin, hemoglobin, transferrin saturation—and its cause must be sought before correction. Neither should be decided in front of a shelf.

What European regulations allow to be said about iron, however, is precise and useful. Seven health claims are associated with it, worded to the letter:

• "Iron contributes to normal formation of red blood cells and hemoglobin."
• "Iron contributes to normal oxygen transport in the body."
• "Iron contributes to normal energy-yielding metabolism."
• "Iron contributes to the reduction of tiredness and fatigue."
• "Iron contributes to normal cognitive function."
• "Iron contributes to the normal function of the immune system."
• "Iron has a role in the process of cell division."

All of them require the product to be at least a "source of iron," meaning 15% of the nutrient reference value (NRV). The NRV being 14 mg, this means 2.1 mg per serving. Note the wording: contributes, normal. None of these phrases describe the treatment of a deficiency, nor do they authorize you to conclude anything about your own situation.

Heme iron vs. non-heme iron: why does absorption change so drastically?

This is the most useful distinction on the subject, and it explains why classifying foods by content can be misleading.

Heme iron is found in hemoglobin and myoglobin: meats, offal, fish, seafood. The iron atom is embedded in a heme molecule, absorbed as such by a dedicated transporter. Its absorbed fraction is high—around 25%—and, importantly, less sensitive to the rest of the meal.

Non-heme iron is found in plants, legumes, cereals, eggs, dairy products, and almost all supplements. Most often ferric (Fe³⁺) and poorly soluble, it must first be reduced to ferrous form (Fe²⁺) to cross the intestinal wall. Its absorbed fraction is much lower—around 10%, often less—and depends heavily on what accompanies it.

A vegetarian or vegan diet therefore provides almost exclusively non-heme iron: a point to be aware of if you rely on plant proteins or spirulina, as the latter is not a reliable source of iron for building intake.

What promotes or blocks iron absorption?

What improves it. Vitamin C is paramount: it reduces ferric iron to ferrous and forms a soluble complex with it that resists inhibitors. This is the only European claim describing the action of one nutrient on another—"Vitamin C increases iron absorption"—and it explains why an orange, a bell pepper, or a kiwi in the same meal genuinely makes a difference. The presence of meat or fish also improves the absorption of plant-based iron from the same meal.

What blocks it. Tea polyphenols—tannins—are the most powerful daily inhibitors, followed by coffee: a cup taken with a meal significantly reduces non-heme iron absorption. The solution is not to give it up but to postpone it by one to two hours. Phytates in whole grains, legumes, and oilseeds play the same role, mitigated by soaking, sprouting, and fermentation. Finally, calcium interferes with both heme and non-heme iron: avoid dairy products or calcium supplements at the same time.

Two other minerals, zinc and magnesium, compete with iron for the same transporters. If you take several products, separate them throughout the day rather than taking them together.

Which foods provide the most?

According to the ANSES Ciqual table, black pudding stands out, largely leading common foods, with entirely heme iron. Offal and liver follow, providing around 8 to 12 mg per 100g, then shellfish—clams, cockles, mussels—and red meats, around 2.5 to 3 mg.

On the plant side, raw contents are surprising: sesame seeds and unsweetened cocoa powder exceed 10 mg per 100g, cooked legumes and tofu are around 2.5 mg, spinach—despite its reputation—around 2 mg. This iron is non-heme, so much less absorbed, and no one eats 100g of cocoa powder.

ANSES recommended daily intakes are 11 mg per day for adult men and women with light to moderate menstrual losses, and 16 mg per day for women with heavier losses. The European labeling NRV, meanwhile, is set at 14 mg.

Bisglycinate, sulfate, gluconate: which form is best tolerated?

The form here is less a matter of effectiveness than of digestive tolerance—this is why so many people abandon supplementation midway.

Ferrous sulfate is the historical benchmark: very inexpensive, well-documented, but often poorly tolerated, as unabsorbed iron remains in the intestinal lumen where it causes discomfort.

Ferrous bisglycinate is a chelate: the iron is bound to two glycine molecules, making it stable in the digestive tract. It partly uses peptide absorption pathways, making it less sensitive to phytates and tannins, and it is significantly better tolerated at the same dose of elemental iron. This is the form we recommend.

Gluconate and ferrous fumarate occupy an intermediate position, better tolerated than sulfate, and more traditional than the chelate. Regardless of the form, one key point to check: the label must state the dose in elemental iron, not the salt's weight.

Who has increased needs, and why consult a doctor?

Several situations increase needs or losses: heavy periods, pregnancy, growing adolescents, diets excluding meat and fish, repeated blood donation, and certain high-volume endurance activities, where digestive losses and some hemolysis due to ground impact are added.

None of these situations justify self-supplementation, for three reasons. An increased need is not a deficiency: many affected individuals have a perfectly normal status. An observed anomaly always has a cause, sometimes more important than the correction itself, and seeking it is part of the consultation. Finally, a part of the population carries a genetic predisposition to iron overload, hemochromatosis, for which supplementation is strictly contraindicated—and one does not know they are affected until it has been investigated.

Medical advice is therefore required before any intake: in case of pregnancy or breastfeeding, for children and adolescents, in case of hemochromatosis or a family history of iron overload, chronic inflammatory disease, kidney failure, during long-term treatment—iron reduces the absorption of several medications, including certain antibiotics and thyroid treatments, which should be spaced out by several hours—and for anyone being monitored for a chronic illness.

One last safety point, often overlooked: iron supplements are among the leading causes of accidental poisoning in young children. Store them out of reach and out of sight, in their original packaging.

Frequently Asked Questions

What are the symptoms of iron deficiency?

Symptoms described in medical literature include unusual fatigue, shortness of breath on exertion, paleness, headaches, feeling cold, brittle nails, and sometimes hair loss. But let's be clear about the value of these signs: they do not allow anyone to conclude. They are shared with dozens of other conditions, they appear late, and an incipient iron deficiency is usually completely silent—reserves are depleted long before hemoglobin drops. Conversely, fatigue attributed to iron often has a completely different cause. The only useful step is a blood test prescribed by a doctor: ferritin, hemoglobin, transferrin saturation. And above all, do not start a supplement before the assessment, as this would skew the results.

Which vitamin should be taken with iron?

Vitamin C, and it's the most cost-effective action in this entire range. This is the only European claim describing the action of one nutrient on another: "Vitamin C increases iron absorption." The mechanism is established—it reduces ferric iron to ferrous form and forms a soluble complex with it that resists phytates and tannins. In practice, a glass of orange juice, a kiwi, or a few slices of bell pepper with the same meal are sufficient; no separate supplement is needed. Many ferrous bisglycinate products already contain it for this reason. Vitamins B12 and B9 are of a different order: they are involved in red blood cell formation, but they do not improve iron absorption.

Which iron is best absorbed?

Two answers depending on whether we are talking about food or supplements. In food, heme iron from meat, offal, fish, and shellfish: absorbed at about 25%, and not very sensitive to the rest of the meal. As a supplement, bisglycinate: chelated with two glycine molecules, it partly uses peptide absorption pathways, is more resistant to phytates and tannins, and is significantly better tolerated than ferrous sulfate at the same dose of elemental iron. Sulfate remains the historical and cheapest reference; gluconate and fumarate occupy an intermediate position. Whatever the form, check that the label states the dose in elemental iron and not the weight of the salt—this is the only way to compare two products.

Why does iron cause diarrhea or constipation?

This is the most common side effect, and the primary reason for discontinuing supplementation. The mechanism is simple: iron absorption is limited, so a significant portion of the dose remains in the intestinal lumen, where it irritates the mucosa and alters the flora. Depending on the individual, this can cause nausea, pain, constipation, or, conversely, accelerated transit—both occur. Black stools, however, are normal and harmless: it is unabsorbed iron. Three strategies significantly improve tolerance: switching from ferrous sulfate to bisglycinate, taking the dose with a snack rather than on an empty stomach, and dividing or spacing out doses. If your doctor has prescribed the dose, discuss any discomfort with them rather than stopping on your own.

What foods prevent iron absorption?

Tea and coffee first, due to their polyphenols; whole grains, legumes, and oilseeds due to their phytates; calcium, dairy or supplemental; to a lesser extent, zinc taken at the same time. All of these only affect the meal concerned: delaying the drink by one to two hours eliminates most of the effect.

How much iron is needed per day?

ANSES recommends 11 mg per day for adult men and women with light to moderate menstrual losses, and 16 mg for women with heavier losses. These values describe population needs, not a dosage: the dose of a supplement, if justified, is set by a doctor.

What foods contain the most iron?

Black pudding significantly outperforms other common foods, followed by offal and liver, shellfish, then red meats. On the plant side: sesame, unsweetened cocoa, legumes, tofu, oilseeds, and green leafy vegetables—with the absorption caveat explained above.

What foods increase ferritin?

No food directly increases ferritin: ferritin is the body's iron reserve, and it increases when absorbed intake consistently exceeds losses. What matters, therefore, is not the stated content of a food but the quantity actually absorbed: red meat, offal, black pudding, and shellfish, whose heme iron is absorbed four times better than plant iron; accompanied by vitamin C; and away from tea, coffee, and dairy products. Two warnings. The timeframe is in months, not days, which makes promises of "rapid recovery" obsolete. And a low ferritin level always has a cause—sometimes more important than the correction itself—which must be investigated by a doctor: diet alone is not enough when there is chronic loss.

When should iron be taken, morning or evening?

The time of day matters little; the context of intake matters a lot: keep it away from tea, coffee, dairy products, and calcium or zinc supplements, and accompany it with a source of vitamin C. On an empty stomach, it is better absorbed but less well tolerated; if it bothers you, take it with a light, dairy-free snack. Your doctor's instructions take precedence over any general recommendation.

Is ferrous bisglycinate dangerous?

The chelated form is no more dangerous than any other: it is even better tolerated digestively. The risk never comes from the form but from the quantity and duration—it is the iron itself, regardless of its presentation, that accumulates if taken without a real need. A bisglycinate dosed at the NRV level and taken on medical advice does not have the same profile as prolonged high-dose intake decided alone.

How to quickly increase iron levels?

The honest answer is that there is no quick fix, and the question is not about a dietary supplement. Rebuilding iron stores takes months, not days: the timelines depend on the cause, the parameter being monitored, and the prescribed dose, and biological control is an integral part of follow-up. Above all, an anomaly always has a cause—digestive losses, heavy periods, malabsorption—and seeking it often matters more than correcting it. Only your doctor can address your situation, choose the method and dose, and say when to stop. Freely sold products, dosed at the reference nutritional value, cover an intake; they do not correct a diagnosed deficiency.

Can iron be taken "preventively," without an assessment?

No, and that is the only answer we will give. Iron is not eliminated, an excess is toxic, and the expected benefit in a person with normal status is nil. This is also why we recommend, for general coverage, a multivitamin without iron rather than with.

What to eat for anemia?

Anemia is a medical diagnosis, and not all anemias are due to iron—some are due to vitamin B12 or folate, others to entirely different causes. Eating "more iron" without knowing the underlying issue is not an answer. See your doctor: management, whether dietary or medicinal, depends on the cause.

What brands can be found in this section?

This section is deliberately the narrowest in the catalog, and it will remain so: we do not stock high-dose iron, as high doses fall under prescription rather than over-the-counter sales. Nutriting offers a bisglycinate whose raw material is identified by its brand name, at a dosage aligned with the nutritional reference value—a coverage level, not a correction. To take advantage of the effect described above, our vitamin C section is the logical complement. The rest of our micronutrition is in the vitamin D, vitamin E, zinc, magnesium, and omega 3 sections; our sports nutrition guide situates each category, and the complete catalog is in sports nutrition.

Advice in a store near Montpellier?

In our store in Vendargues, about ten minutes from Montpellier, iron is the section where we most often refer to a doctor, and we stand by that. We can explain what a bisglycinate is, why it is better tolerated than a sulfate, and how far from tea to take it. We will never tell you if you are deficient: that is read on a blood test, not over a counter. We ship everywhere in France and Europe.

Sources: ANSES for nutritional references and opinions on food supplements, Ciqual for food content, EFSA for authorized claims.

To learn more: ferrous bisglycinate, tolerance and absorption.