Iron ranks as the fourth most abundant element on earth and remains one of the most studied mineral nutrients in human health. It forms a core component of haemoglobin (the oxygen-carrying protein in red blood cells) and myoglobin (which stores oxygen in muscles), and it participates in hundreds of enzymatic reactions throughout the body [1].

Beyond oxygen transport, iron plays roles in DNA synthesis and repair, energy production in mitochondria, neurotransmitter synthesis, and immune function. The central nervous system, cardiovascular system, and endocrine system all depend on adequate iron levels to function properly.

Here’s the paradox though: despite being abundant in the earth’s crust and present in many foods, iron deficiency remains the most common nutritional deficiency worldwide, affecting roughly 30% of the global population according to the World Health Organisation [2].

Two forms of dietary iron

Iron in food comes in two distinct forms, and this distinction matters quite a bit for absorption:

Haem iron comes exclusively from animal sources, particularly red meat, poultry, and fish. The body absorbs haem iron efficiently, typically 15-35% of what you consume. This high absorption rate occurs because haem iron enters intestinal cells intact, bypassing many of the regulatory mechanisms that limit non-haem iron uptake.

Non-haem iron is found in both plant and animal foods. Leafy greens, legumes, fortified cereals, and nuts all contain non-haem iron. However, absorption rates hover around 2-20%, and many dietary factors can interfere. Phytates in whole grains, polyphenols in tea and coffee, and calcium can all reduce non-haem iron absorption. On the flip side, vitamin C significantly enhances non-haem iron uptake.

This explains why vegetarians and vegans face higher risks of iron deficiency despite sometimes consuming adequate amounts on paper.

What are the evidence-based benefits of iron?

1. Iron deficiency anaemia treatment

Iron deficiency anaemia occurs when the body lacks sufficient iron to produce adequate haemoglobin. Without enough haemoglobin, red blood cells become smaller and paler (microcytic hypochromic anaemia), and their oxygen-carrying capacity drops.

Common symptoms include:

Persistent fatigue that doesn’t improve with rest
Shortness of breath during normal activities
Pale skin, particularly noticeable in the nail beds and inner eyelids
Cold hands and feet
Brittle or spoon-shaped nails
Restless leg syndrome
Unusual cravings for non-food items (pica)

Different groups face varying risks. Infants and young children top the list due to rapid growth and often limited dietary variety. Women of reproductive age come next, with menstrual blood loss accounting for significant iron depletion each month. Pregnant women require substantially more iron to support fetal development and expanded blood volume.

In men and postmenopausal women, iron deficiency often signals occult gastrointestinal bleeding, which warrants investigation for conditions like ulcers, polyps, or colorectal cancer.

Treatment typically begins with dietary modification, emphasising iron-rich foods like red meat, organ meats, legumes, and dark leafy vegetables [3]. When diet alone proves insufficient, or when anaemia is severe, iron supplements become necessary. The NHS recommends that most people with iron deficiency anaemia take 100-200mg of elemental iron daily, usually as ferrous sulphate tablets [4].

For severe anaemia (haemoglobin below 8 g/dL) with symptoms like rapid breathing, chest pain, or extreme fatigue, blood transfusion may be required as an immediate intervention.

2. Postpartum depression

Postpartum depression affects between 13-19% of new mothers, typically emerging within the first month after delivery. Unlike the “baby blues” that resolve within two weeks, postpartum depression persists and can significantly impair maternal functioning and infant bonding.

The condition involves sustained low mood, intense sadness, loss of interest in activities, feelings of worthlessness, and sometimes thoughts of self-harm. Hormonal fluctuations, sleep deprivation, and the overwhelming demands of caring for a newborn all contribute to its development.

What’s less commonly discussed is the potential role of iron status. Pregnancy depletes iron stores substantially, and blood loss during delivery compounds this. A double-blind controlled study involving 70 postpartum mothers over six weeks found that iron supplementation not only replenished ferritin (iron storage protein) levels but also improved depression outcomes [5].

The supplemented group showed 42.8% improvement in depression scores compared with 20% in the placebo group. Perhaps more telling: among women whose depression persisted, 27.1% were iron deficient, compared with just 4.5% of those who improved.

This doesn’t mean iron supplements treat postpartum depression in all cases. But it does suggest that checking iron status should be routine in women experiencing postpartum mood difficulties.

3. Childhood migraines

Migraines aren’t just an adult problem. Roughly 5% of children between ages 5 and 15 experience migraines, and these attacks can significantly disrupt school attendance and quality of life. If migraines occur more than 3-4 times monthly and interfere with daily activities, medical attention is warranted.

A controlled study of 98 children aged 5 to 15 years examined the relationship between iron status and migraine characteristics [6]. Children with iron deficiency experienced more frequent migraines, greater severity, and higher disability scores compared to iron-sufficient peers.

When iron supplementation was combined with topiramate (a preventive migraine medication), researchers observed reductions in attack frequency, severity, and duration, along with improved paediatric migraine disability assessments.

The mechanism isn’t entirely clear, but iron’s role in neurotransmitter synthesis and oxygen delivery to brain tissue likely contributes. Serotonin and dopamine synthesis both require iron-dependent enzymes, and these neurotransmitters play important roles in migraine pathophysiology.

4. Children’s cognitive development

Nutritional status during pregnancy and early childhood shapes brain development in ways that persist throughout life. Iron deficiency during these critical periods can have lasting consequences.

Iron is essential for myelination (the formation of protective sheaths around nerve fibres), neurotransmitter production, and energy metabolism in the brain. The developing brain has particularly high iron demands, and deficiency during pregnancy or infancy can impair cognitive function even after iron status normalises [7].

A cohort study following 676 children aged 7 to 9 years examined the effects of prenatal nutritional supplementation [8]. Pregnant women who received iron and folic acid supplementation had children who performed better on measures of intellectual development, working memory, inhibitory control, and motor function. This association was particularly strong in regions with high baseline iron deficiency rates.

The long-term implications extend beyond cognition. Prenatal nutritional imbalances have been linked to increased risk of type 2 diabetes, dyslipidaemia, hypertension, and coronary heart disease in adulthood. The “developmental origins of health and disease” hypothesis suggests that nutrient availability during fetal development programmes metabolic responses that persist throughout life.

5. Attention deficit hyperactivity disorder (ADHD)

ADHD affects approximately 5-15% of school-age children, characterised by extreme hyperactivity, impulsivity, and inattention that impairs academic performance and social relationships.

The causes remain complex and not fully understood. Known contributing factors include maternal smoking and stress during pregnancy, alcohol and drug exposure, environmental chemicals and heavy metals, artificial food colourings, low birth weight, and preterm birth.

Some researchers have explored whether nutritional deficiencies, including iron, might play a role. A 12-week controlled study of 23 children with ADHD (who did not have anaemia) found that iron supplementation reduced ADHD symptom scores compared with placebo [9].

However, a systematic review examining 11 randomised controlled trials reached a more cautious conclusion [10]. The authors found no significant evidence that iron, zinc, or magnesium supplementation improves ADHD symptoms in children generally. This doesn’t rule out benefits for children who are genuinely deficient, but it does suggest that iron supplements shouldn’t be seen as a treatment for ADHD in the absence of documented deficiency.

Side effects and safety concerns

At recommended doses, iron supplements are relatively safe, though gastrointestinal side effects occur commonly. These include:

Nausea and vomiting
Heartburn
Abdominal cramping
Constipation (more common) or diarrhoea
Dark-coloured stools (this is normal and not harmful)

Taking iron with food reduces these symptoms, though it also reduces absorption somewhat. Some people find that switching to a different iron formulation (ferrous gluconate or ferrous fumarate instead of ferrous sulphate) helps with tolerability.

The upper tolerable intake for adults and adolescents aged 14 and over is 45mg of elemental iron daily [11]. This includes pregnant and breastfeeding women. Exceeding this level chronically increases the risk of adverse effects.

Iron toxicity

Acute iron poisoning typically occurs in children who accidentally ingest iron supplements meant for adults. Symptoms begin with abdominal pain, vomiting, and bloody diarrhoea. In severe cases (doses exceeding 20-60mg/kg body weight), symptoms can progress to:

Rapid pulse
Low blood pressure
Fever
Difficulty breathing
Confusion or coma

If someone survives the initial phase, symptoms may temporarily improve before deteriorating again 12-48 hours later, with potential damage to the liver, kidneys, cardiovascular system, and central nervous system.

Keep iron supplements well out of reach of children. Seek immediate medical attention if accidental ingestion occurs.

Who should avoid iron supplements?

People without documented deficiency: Don’t take iron supplements “just in case.” Excess iron accumulates in organs and causes damage. Get your iron status checked before supplementing.
Hereditary haemochromatosis patients: This genetic condition causes excessive iron absorption and storage. Even the tolerable upper intake (45mg/day) can cause toxicity in affected individuals.
People with liver disease: The liver stores iron, and liver disease can impair iron regulation.
Those taking certain medications: Iron reduces absorption of levodopa (for Parkinson’s disease), levothyroxine (for thyroid conditions), certain antibiotics, and ACE inhibitors. These medications can also reduce iron absorption. Separate doses by at least 2 hours.
People consuming high-dose vitamin C: Vitamin C dramatically increases iron absorption. This is helpful for those with deficiency but potentially dangerous for those with normal or elevated iron stores. If you take several grams of vitamin C daily, be cautious about combining it with iron supplements.

A note on iron and chronic disease

Observational studies have found associations between elevated body iron stores and increased risk of cardiovascular disease, type 2 diabetes, and certain cancers. The mechanisms aren’t fully established, but iron’s ability to catalyse oxidative reactions may contribute to tissue damage over time.

This doesn’t mean dietary iron causes disease. But it does reinforce the principle that more isn’t better. Iron supplementation should be targeted at those with deficiency, not used as a general “health booster.”

References

Abbaspour N, Hurrell R, Kelishadi R. Review on iron and its importance for human health. J Res Med Sci. 2014;19(2):164-174. PMID: 24778671
World Health Organisation. Anaemia. https://www.who.int/health-topics/anaemia
Lopez A, Cacoub P, Macdougall IC, Peyrin-Biroulet L. Iron deficiency anaemia. Lancet. 2016;387(10021):907-916. PMID: 26314490
NHS. Iron deficiency anaemia - Treatment. https://www.nhs.uk/conditions/iron-deficiency-anaemia/treatment/
Albacar G, Sans T, Martín-Santos R, et al. An association between plasma ferritin concentrations measured 48h after delivery and postpartum depression. J Affect Disord. 2011;131(1-3):136-142. PMID: 21130502
Gholamreza-Mirzaee M, Ghazavi A, Mosayebi G, Shafiei M. Relationship between serum ferritin level and migraine in children. Iran J Child Neurol. 2016;10(2):51-58. PMID: 27222700
Georgieff MK. Iron deficiency in pregnancy. Am J Obstet Gynecol. 2020;223(4):516-524. PMID: 32184147
Christian P, Murray-Kolb LE, Khatry SK, et al. Prenatal micronutrient supplementation and intellectual and motor function in early school-aged children in Nepal. JAMA. 2010;304(24):2716-2723. PMID: 21177506
Konofal E, Lecendreux M, Deron J, et al. Effects of iron supplementation on attention deficit hyperactivity disorder in children. Pediatr Neurol. 2008;38(1):20-26. PMID: 18054688
Händel MN, Rohde JF, Ritskes-Hoitinga M, et al. Efficacy and safety of iron therapy on attention-deficit/hyperactivity disorder in children: A systematic review of randomized controlled trials. Clin Nutr. 2016;35(1):100-108. PMID: 26445630
National Institutes of Health Office of Dietary Supplements. Iron Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/