Iron

Also known as: Fe, Ferrous sulfate, Iron bisglycinate

An essential mineral that carries oxygen in the blood; the most common nutrient deficiency in the world.

Editorial review by the IngredientWiki Editorial Team
Updated 2026-09-26
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Watercolor study of an iron-rich mineral, lentils, and leafy greens — Editorial illustration

Iron supplements treat documented iron deficiency and iron-deficiency anemia, including clinically managed needs during pregnancy. Fatigue alone does not diagnose deficiency, and unnecessary iron can cause harm or delay evaluation of bleeding, malabsorption, or another condition.^{1, 2}

Core component of hemoglobin and myoglobin (oxygen transport)^{1, 2}
Heme iron from meat is better absorbed than non-heme iron from plants^{1, 2}
Recommended intake: 8 mg daily for men, 18 mg for women aged 19–50^{1, 2}
Iron supplements are a leading cause of accidental poisoning in children^{1, 2}

What is Iron?

Iron does one thing extraordinarily well: bind and release oxygen. Most of the body's iron sits inside hemoglobin, with the rest in myoglobin, enzymes, and storage proteins like ferritin. Because iron is tightly recycled — red blood cells are broken down and rebuilt — daily losses are small, which is why adult men rarely need supplements. Premenopausal women, pregnant women, growing children, and vegetarians are the groups most likely to need extra iron.^{1, 2}

Where it comes from

Natural sources

Heme iron: red meat, poultry, fish, and shellfish
Non-heme iron: beans, lentils, tofu, spinach, fortified cereals
Cast-iron cookware (adds small amounts to food)

How it's made

Supplemental iron is produced as iron salts — ferrous sulfate, ferrous gluconate, ferrous fumarate, and chelated forms like ferrous bisglycinate.

What it does in products

Benefits

Treating iron-deficiency anemia

strong evidence

Iron supplementation reliably raises hemoglobin in people with iron-deficiency anemia, improving fatigue, exercise capacity, and concentration over 4–8 weeks.^{1, 2}

Iron treats iron-deficiency anemia when the diagnosis and cause are established; indiscriminate supplementation can delay evaluation of blood loss or another condition.

Preventing deficiency in pregnancy

strong evidence

Blood volume expands dramatically in pregnancy, doubling iron needs to 27 mg daily. Supplementation is standard care and reduces the risk of maternal anemia and low birth weight.¹

Pregnancy increases iron requirements, but screening, formulation, dose, and management of anemia belong within prenatal care.

Restoring levels in athletes and vegetarians

moderate evidence

Endurance athletes and plant-based eaters have higher iron losses or lower absorption. Periodic supplementation corrects low ferritin, which is associated with reduced performance.^{1, 2}

People with low intake or iron losses may benefit after deficiency is confirmed; athletes and vegetarians are not automatically deficient.

Reducing restless legs symptoms

moderate evidence

In people with iron deficiency, restless legs syndrome symptoms often improve when iron stores are restored.^{3, 1}

Cochrane evidence supports iron in some people with restless legs syndrome, particularly when iron stores are low; route and baseline ferritin matter.

Evidence scope and limitations

The review addresses diagnosed iron deficiency and iron-deficiency anemia, pregnancy requirements, at-risk dietary patterns, and selected restless-legs treatment evidence.

Symptoms such as fatigue are nonspecific and should not be used to self-diagnose iron deficiency.
Oral and intravenous iron have different indications and risks; this page does not provide an individual treatment plan.

Evidence last checked: 2026-09-26

Side effects & safety

Constipation (common)The classic iron side effect; gentler chelated forms, lower doses, or every-other-day dosing reduce it.

Nausea and stomach discomfort (common)Taking iron with food reduces nausea but also reduces absorption; chelated forms are gentler.

Dark stools (common)Harmless and expected with iron supplements.

Accidental overdose toxicity (rare)Iron is highly toxic in overdose, especially for children. Keep supplements locked away.

Safety considerations

Iron is recommended during pregnancy (27 mg daily) and is a standard component of prenatal vitamins. Iron tablets should be kept out of reach of children.
Calcium, tea, coffee, and high-phytate foods reduce iron absorption; take iron apart from these.
Vitamin C significantly improves absorption of non-heme iron.
Iron reduces absorption of certain antibiotics and thyroid medication; separate doses by at least 2 hours.
Not for: Hemochromatosis (iron overload disorder)
Not for: Do not supplement iron without testing if you are an adult male or postmenopausal woman with adequate levels

^{1, 2}

Amounts studied & product use

These figures describe research or common product use, not a personal dose or treatment recommendation.

In supplement studies and products

U.S. iron requirements vary by age, sex, and pregnancy status. Treatment trials use measured elemental-iron regimens after deficiency is confirmed; daily versus alternate-day schedules and the appropriate amount depend on laboratory findings, formulation, tolerance, and clinical supervision.

^{1, 2}

Regulatory status

Dietary supplement under DSHEA. Iron is also an FDA-approved over-the-counter drug ingredient for treating iron-deficiency anemia when labeled accordingly.
GRAS (generally recognized as safe) for food use.

⁴

Heme vs non-heme iron

Heme iron, from animal foods, is absorbed at roughly 15–35% regardless of the rest of the meal. Non-heme iron, from plants and supplements, is absorbed at 2–20% and is strongly influenced by enhancers and inhibitors: vitamin C and meat protein boost it, while tannins (tea, coffee), calcium, and phytates (whole grains, legumes) block it. This is why vegetarians need about 1.8 times the standard iron recommendation, and why taking plant iron with vitamin C is a useful habit.

^{1, 2}

Frequently asked questions

How do I know if I need an iron supplement?

Signs of deficiency include fatigue, pale skin, shortness of breath, and brittle nails, but the only reliable way is a blood test measuring hemoglobin and ferritin. Adult men and postmenopausal women should not supplement iron without testing, since excess iron accumulates in the body.^{1, 2}

What is the best time to take iron?

On an empty stomach for maximum absorption, but with food if it causes nausea. Take it with vitamin C or orange juice, and at least an hour away from coffee, tea, dairy, and calcium supplements.^{1, 2}

How long does it take for iron supplements to work?

Hemoglobin typically rises within 2–4 weeks, but ferritin stores take 2–3 months to replenish. Doctors often retest after 8–12 weeks to confirm the dose is working.^{1, 2}

The bottom line

Iron is highly effective when deficiency is confirmed and poorly suited to guesswork. Testing and identifying the cause are more important than choosing a heavily marketed formulation.

References

Iron: Health Professional Fact Sheet. NIH Office of Dietary Supplements (2025) · government guidance
Iron Deficiency Anemia. StatPearls, National Library of Medicine (2025) · ingredient monograph · NBK448065
Iron for the treatment of restless legs syndrome. Cochrane Database of Systematic Reviews (2019) · systematic review · PMID 30609006
Dietary Supplements. U.S. Food and Drug Administration (2025) · government guidance

Revision history

2026-09-26Replaced search-result citations with exact sources, mapped claims to evidence, and reassessed evidence strength.