Iron deficiency: how to regain energy?

Fatigue that persists despite a full night's sleep, shortness of breath during exercise, a complexion losing its radiance. These signs, often attributed to one's lifestyle, can indicate an iron deficiency. This mineral is both one of the most studied in nutrition and one of the most common deficiencies among women.

The subject is worth looking into closely. An iron deficiency does not appear suddenly: it sets in in stages. Stores are depleted first, then red blood cell production is affected. Understanding this chronology helps you know when to be concerned, what to measure, and how to adjust your intake to regain your energy.

The adult body contains approximately 3 to 4 grams of iron. Nearly two-thirds circulate in the hemoglobin of red blood cells. The rest is distributed between muscle myoglobin, cellular enzymes, and stores kept in the form of ferritin, primarily in the liver.

Iron contributes to the normal transport of oxygen in the body and to the normal formation of red blood cells and hemoglobin. Each hemoglobin molecule carries four iron atoms. Each one binds an oxygen molecule in the lungs and then releases it into the tissues.

Its role does not end with the blood. Inside mitochondria, iron is a component of cytochromes and iron-sulfur centers in the respiratory chain. This is where oxygen is used to produce ATP, the cell's energy currency. Iron thus contributes to normal energy-yielding metabolism and to the reduction of tiredness and fatigue.

This dual role explains why an iron deficiency in the body is felt first in energy levels, even before any change in blood count: iron ensures both the transport of oxygen and its utilization by the cell. Iron also contributes to normal cognitive function and the normal function of the immune system.

Dietary iron exists in two forms, which differ significantly in their absorption:

• Heme iron is present in meat, offal, and fish. It is incorporated into the heme of animal hemoglobin and myoglobin. It uses a dedicated intestinal absorption pathway, with an absorption rate of approximately 15 to 35%.
• Non-heme iron is present in plants, eggs, and dairy products. Its absorption depends more on the composition of the meal: it varies from 2 to 20% depending on the facilitators and inhibitors present (Hurrell and Egli, 2010).

One final physiological element sheds light on the rest: the body has no active pathway to eliminate excess iron. Balance rests entirely on absorption, which is controlled by a hormone produced by the liver called hepcidin. When stores are full, hepcidin inhibits absorption; when they drop, the body absorbs more.

An iron deficiency progresses in three stages:

• First stage: stores diminish without other measurable consequences. This is low ferritin, which biology refers to as hypoferritinemia.
• Second stage: the supply of iron to tissues becomes limiting.
• Third stage: hemoglobin levels drop in turn: this is the stage of a significant iron deficiency.

The signs described below can appear as early as the first stage. However, they are not specific, as fatigue has many possible origins. Only a blood test, requested by a healthcare professional, can confirm an iron deficiency in the blood and determine its stage.

Fatigue is the most frequent signal. It is distinguished from ordinary fatigue by its persistence during rest and by slow recovery after exertion. Shortness of breath during moderate effort, such as climbing stairs, reflects a reduced capacity to transport oxygen.

This link between stores and energy has been studied in women whose hemoglobin was normal. In a randomized, placebo-controlled trial, 198 menstruating women reported unexplained fatigue and ferritin levels below 50 µg/L. They received iron or a placebo for 12 weeks. Fatigue decreased by approximately 48% in the iron group, compared to 29% in the placebo group (Vaucher et al., 2012). The benefit was more pronounced in participants with the lowest ferritin levels.

The cognitive sphere is also affected: decreased concentration, a feeling of intellectual slowness, irritability. Iron is indeed involved in the synthesis of several neurotransmitters, including dopamine. Some people also report increased sensitivity to cold and lower resistance to daily stress. The link between iron deficiency and stress remains largely descriptive to date. When fatigue and nervous tension set in together, other nutrients come into play: magnesium contributes to the reduction of tiredness and fatigue and to normal psychological functions, an approach developed in our sleep and stress management selection.

The question of the link between iron deficiency and low blood pressure often arises. Low blood pressure is not a recognized marker of iron status. The dizziness and lightheadedness that sometimes accompany an advanced deficiency are mainly due to reduced tissue oxygenation.

Skin, skin appendages (hair/nails), and mucous membranes are tissues with rapid turnover. They are among the first to reflect an insufficient supply of oxygen and nutrients. This is where health becomes visible, literally.

The complexion can become pale or dull. Pallor is often more visible inside the lower eyelids and on the nail beds. Nails can become thin, brittle, ridged, and in advanced cases, concave (spoon-shaped). Hair may lose density, with more diffuse shedding than usual.

These signs vary according to individual profiles. On dark or tanned skin, pallor is less visible on the face than on the mucous membranes and palms of the hands. For women, fragile nails and decreased hair density are often the signs that motivate the first consultation.

A dangerous iron deficiency in the strict sense mainly concerns advanced stages, when hemoglobin drops and the heart compensates by beating faster. Palpitations or shortness of breath at the slightest exertion require immediate consultation.

An iron deficiency always results from an imbalance between what is absorbed and what is lost or consumed. Some profiles combine increased needs with less easily absorbed intakes.

Menstrual losses represent an average of 15 to 20 mg of iron per cycle, and more in cases of heavy periods. The EFSA thus sets the nutritional reference at 16 mg per day for premenopausal women, compared to 11 mg for men (EFSA, 2015). A balanced 2,000 kcal diet rarely provides more than 12 to 14 mg, of which only a fraction is absorbed.

Pregnancy multiplies requirements. The increase in blood volume, the development of the placenta, and the formation of fetal stores mobilize nearly one gram of additional iron over nine months. The body partially compensates by absorbing more during the second and third trimesters. This is not always enough when initial stores are modest. Breastfeeding, and then closely spaced pregnancies, can prolong this deficit. In case of pregnancy or breastfeeding, it is important to seek advice from a healthcare professional before any supplementation.

A vegetarian or vegan diet can meet iron requirements, but it relies exclusively on non-heme iron, which is less well absorbed. A meta-analysis has shown that, on average, vegetarians have lower ferritin levels than omnivores, even with comparable total intakes (Haider et al., 2018). The issue, therefore, is not the quantity ingested, but rather the assimilation.

In endurance athletes, several mechanisms compound this:

• Red blood cell destruction due to repeated impacts, particularly in running.
• Loss through sweat and the digestive tract during long efforts.
• Increased hepcidin for 3 to 6 hours after intense effort, which reduces iron absorption from the following meal (Peeling et al., 2008).

Female runners combine these factors with menstrual losses.

The question of iron deficiency and weight loss arises mainly in a specific sense. It is not an iron deficiency that causes weight loss. It is restrictive diets, particularly those that exclude meat without compensation, that reduce intake. Any prolonged caloric restriction therefore deserves special attention to iron status.

Non-heme iron absorption is very sensitive to other components of the meal:

• Phytates in whole grains, legumes, and oilseeds form insoluble complexes with iron.
• Tannins and polyphenols in tea and coffee can reduce iron absorption from a meal by 50 to 70% when consumed during or immediately after it (Hurrell et al., 1999).
• Calcium is the only inhibitor that acts on both forms of iron. Its effect depends on the dose: 300 mg in a single meal is enough to significantly reduce absorption (Hallberg et al., 1991).
• PPIs. Gastric acidity is necessary to convert non-heme iron into an absorbable form. Prolonged use of proton pump inhibitors, which reduce this acidity, is associated with a lower iron status. This subject should be discussed with a pharmacist or doctor.

Before any supplementation, the plate remains the first lever for dealing with an iron deficiency. The challenge is not just to choose iron-rich foods, but to compose meals that promote its assimilation.

The most concentrated sources of heme iron are, in order:

• black pudding and organ meats (poultry liver, kidneys)
• seafood, particularly clams and mussels
• red meat (beef, lamb, horse), which provides an average of 2 to 3.5 mg of iron per 100 g
• fish and poultry, which are significantly less rich

Liver is also very rich in vitamin A, which is why its consumption is not recommended during pregnancy. For other profiles, one to two servings of red meat per week, supplemented by seafood, provide a well-assimilated iron base.

Another lesser-known benefit: muscle proteins from meat, fish, and poultry improve the absorption of non-heme iron consumed in the same meal. This is the "meat factor."

The main plant sources of iron are:

• legumes (lentils, chickpeas, dried beans) and tofu
• pumpkin and sesame seeds and oilseeds
• whole grains
• some leafy green vegetables, such as parsley

Spinach owes its reputation to a long-overestimated content; furthermore, its oxalates strongly limit the assimilation of its iron.

Several preparation techniques reduce phytate content and increase the proportion of absorbable iron: prolonged soaking of legumes and grains, sprouting, and fermentation (sourdough bread, tempeh, miso).

The most effective combination has been known for several decades: vitamin C increases the absorption of non-heme iron. In a benchmark study, adding 50 mg of ascorbic acid to a phytate-rich meal was enough to largely counteract their inhibitory effect (Hallberg et al., 1989). In practice, a raw bell pepper, a few citrus wedges, a kiwi, or a handful of fresh parsley in a lentil dish significantly change its nutritional value.

Conversely, three habits hinder absorption:

• tea or coffee at the end of a meal (it is better to space them out by at least an hour);
• cheese or yogurt in the same meal as an iron source, when trying to optimize every intake; large quantities of unfermented whole grains.

Cooking in a cast-iron pot can also slightly increase the iron content of stews, especially acidic ones like a tomato sauce.

These adjustments are often sufficient when reserves are simply low. They reach their limits when ferritin is severely depleted or when requirements are chronically increased.

When blood tests confirm an iron deficiency, diet alone rarely allows for the rapid replenishment of very low reserves. An iron-rich dietary supplement then takes over. Its choice is based on three criteria: the form of iron, associated nutrients, and the duration of intake.

One principle takes precedence over others: iron should not be taken "just in case." The body does not know how to eliminate excess iron, and supplementation without prior testing can lead to overload, particularly in men and postmenopausal women. Iron supplements must also be kept out of the reach of children.

Classic ferrous salts, such as ferrous sulfate, are effective but often poorly tolerated. A meta-analysis of 43 trials showed a significantly increased frequency of digestive discomfort with ferrous sulfate compared to placebo: gastric heaviness, cramps, altered transit (Tolkien et al., 2015). This discomfort is the primary cause of premature discontinuation, and thus failure of supplementation.

Chelated forms, such as iron bisglycinate, bind iron to two glycine molecules, making it less reactive in the digestive tract. A meta-analysis of randomized trials observed comparable effects on ferritin and hemoglobin, with less digestive discomfort than ferrous salts (Fischer et al., 2023).

Microencapsulation technologies (liposomal iron, microencapsulated pyrophosphate) pursue the same goal: preserving iron until its site of absorption to improve digestive tolerance. This logic of bioavailability is at the heart of the approach of Biocyte, the leading French nutricosmetics laboratory, which integrated microencapsulation into its formulas in 2016.

The frequency of intake counts as much as the form. Iron intake raises hepcidin for about 24 hours, which reduces the absorption of a next dose if taken too soon. In women with low reserves, taking iron every other day has allowed for higher fractional absorption than daily intake, for the same total quantity (Stoffel et al., 2017). This schedule should be discussed with a healthcare professional.

A relevant formula is not just about iron:

• Vitamin C increases iron absorption and helps reduce fatigue;
• vitamins B9 (folates) and B12 contribute to the normal formation of red blood cells and to the reduction of fatigue, on the same production chain as iron;
• vitamin B2 and vitamin A contribute to normal iron metabolism;
• copper contributes to normal iron transport.

This integrative approach, which combines several nutrients on the same biological mechanism, distinguishes a functional nutrition formulation from simple isolated intake.

The timing of intake is also important. An iron dietary supplement is ideally taken away from tea, coffee, and dairy products. If digestive discomfort occurs on an empty stomach, taking it with a light meal improves tolerance.

Replenishing reserves is slow. Energy often returns in a few weeks, but ferritin generally takes two to three months to rise significantly, sometimes longer in cases of severe iron deficiency. Stopping intake as soon as fatigue fades exposes you to a rapid return to square one.

Monitoring is based on ferritin levels, ideally associated with a complete blood count and transferrin saturation coefficient, about three months after starting supplementation. Ferritin can also rise independently of reserves in certain physiological situations, which sometimes makes it falsely reassuring. Its interpretation should therefore be left to a healthcare professional.

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• Hurrell R., Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr, 2010;91(5):1461S-1467S.

• EFSA NDA Panel. Scientific Opinion on Dietary Reference Values for iron. EFSA Journal, 2015;13(10):4254.

• Haider L.M. et al. The effect of vegetarian diets on iron status in adults: a systematic review and meta-analysis. Crit Rev Food Sci Nutr, 2018;58(8):1359-1374.

• Peeling P. et al. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. Eur J Appl Physiol, 2008;103(4):381-391.

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• Fischer J.A.J. et al. The effects of oral ferrous bisglycinate supplementation on hemoglobin and ferritin concentrations in adults and children: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev, 2023;81(8):904-920.

• Stoffel N.U. et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women. Lancet Haematol, 2017;4(11):e524-e533.

• WHO. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Geneva, 2020.

• Peyrin-Biroulet L. et al. Guidelines on the diagnosis and treatment of iron deficiency across indications: a systematic review. Am J Clin Nutr, 2015;102(6):1585-1594.

• Trost L.B., Bergfeld W.F., Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol, 2006;54(5):824-844.