Minerals

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.

By IngredientWiki Editorial Team
Fact-checked by IngredientWiki Editorial Team
Updated 2026-09-25
3 min read

In short

Iron is an essential mineral and the core of hemoglobin, the protein in red blood cells that carries oxygen from the lungs to every tissue. Iron deficiency is the most common nutritional deficiency worldwide and the leading cause of anemia. Iron supplements are used to prevent and treat deficiency, with ferrous sulfate being the classic form and gentler options like iron bisglycinate gaining popularity.

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

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.

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.

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.

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.

Reducing restless legs symptoms

moderate evidence

In people with iron deficiency, restless legs syndrome symptoms often improve when iron stores are restored.

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

How it's used

In supplements

For prevention: 8–18 mg daily depending on age and sex. For treating deficiency, doctors commonly prescribe 60–120 mg of elemental iron daily or every other day — every-other-day dosing improves absorption and tolerance. Bisglycinate is gentler than sulfate at equivalent doses.

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.

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.

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.

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.

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.

The bottom line

Iron is essential but unlike most supplements, it should be taken only when needed — confirmed by blood tests — because excess iron accumulates. For those who do need it, choosing a gentle form, pairing with vitamin C, and separating it from coffee and dairy make supplementation far more tolerable and effective.

References

Iron — Health Professional Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
Iron — Consumer Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-Consumer/
Iron compound summary. PubChem (National Library of Medicine). https://pubchem.ncbi.nlm.nih.gov/compound/23925
Iron deficiency anemia. StatPearls (National Library of Medicine). https://www.ncbi.nlm.nih.gov/books/NBK448065/