Iron

mineraliron atom

Best with a mealTake with food

What is it

Iron is an essential mineral that forms the core of hemoglobin, the protein in red blood cells that carries oxygen from lungs to tissues. It is also found in myoglobin (muscle), and many enzymes involved in energy production.

How it works

About two-thirds of body iron is in hemoglobin; most of the rest is stored as ferritin in the liver, spleen, and bone marrow. The body recycles iron from old red blood cells, so daily losses (around 1 mg from shed cells and bleeding) are normally small. Dietary iron comes in two forms: heme iron from animal foods (absorbed 15 to 35 percent) and non-heme iron from plants and supplements (absorbed 2 to 20 percent). Vitamin C boosts non-heme absorption; tannins (tea), calcium, and phytate inhibit it. The body cannot actively excrete iron, so absorption is the main regulator of iron balance — and excess is a problem.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Iron deficiency anemia treatment

Grade A

Strong evidence

Iron supplementation reliably corrects iron deficiency anemia with normalization of hemoglobin over weeks to months. Standard treatment for the condition.

Pregnancy outcomes

Grade A

Strong evidence

Iron supplementation in pregnancy reduces maternal anemia and improves outcomes including birthweight. Standard in prenatal care.

Iron deficiency without anemia (low ferritin)

Grade B

Good evidence

Even before anemia develops, iron deficiency causes fatigue and reduced exercise tolerance. Supplementation improves symptoms in deficient individuals.

Restless legs syndrome

Grade B

Good evidence

RLS is associated with low brain iron. Supplementation in people with low ferritin (below about 75 mcg/L) often reduces symptoms.

Athletic performance in deficient athletes

Grade B

Good evidence

Iron supplementation improves endurance performance in deficient endurance athletes, especially female athletes. Replete athletes do not benefit from additional iron.

5 commercial forms

Ferrous sulfate

standard form, well absorbed, common side effects

The standard iron salt used in most prescription iron and in many supplements. Inexpensive and effective; commonly causes nausea and constipation.

Ferrous gluconate / fumarate

well absorbed, somewhat gentler

Alternative salts with similar absorption to sulfate. Some people find them slightly more tolerable.

Ferric pyrophosphate / heme iron polypeptide

lower absorption, much gentler

Often marketed as gentle iron. Heme iron polypeptide is derived from animal blood. Lower elemental dose per pill but better tolerated.

Iron bisglycinate

chelated form, gentler on stomach

Bound to glycine. Better tolerated than ferrous sulfate at equivalent elemental iron doses; absorption similar to slightly better than ferrous sulfate.

Carbonyl iron

slowly absorbed, less acute toxicity risk

Pure iron particles slowly converted to absorbable form in stomach acid. Lower risk of acute overdose because absorption is gradual.

Dosage

The RDA is 8 mg per day for adult men and women over 50, and 18 mg for premenopausal women. Pregnant women need 27 mg. Common iron supplements provide 18 to 65 mg of elemental iron. The tolerable upper limit for adults is 45 mg per day. People with diagnosed iron deficiency anemia are often prescribed 60 to 200 mg of elemental iron daily under medical supervision.

When and how to take it

Iron absorbs best on an empty stomach with vitamin C (such as a glass of orange juice), but this also maximizes side effects. Many people tolerate iron better when taken with a small meal, even though absorption is somewhat reduced. Recent research suggests that alternate-day iron dosing (rather than daily) and once-daily morning dosing may improve absorption efficiency by avoiding the body's down-regulation of absorption. Avoid taking iron with calcium, dairy, tea, coffee, or whole-grain meals that contain phytate, since these reduce absorption.

Food sources

Food	Amount	%DV
Oysters (cooked), 3 oz	8 mg	44%
Beef liver, 3 oz cooked	5 mg	28%
Lentils (boiled), 1/2 cup	3 mg	17%
Spinach (boiled), 1/2 cup	3 mg	17%
Beef (chuck), 3 oz cooked	2.7 mg	15%
Tofu (firm), 1/2 cup	3.4 mg	19%
White beans (canned), 1/2 cup	4 mg	22%
Dark chocolate (45-69%), 1 oz	2.3 mg	13%
Fortified breakfast cereal	18 mg per serving	100%
Pumpkin seeds, 1 oz roasted	2.5 mg	14%

Safety

Iron supplements commonly cause nausea, constipation, dark stools, and stomach upset, especially at higher doses. Acute overdose is one of the leading causes of poisoning deaths in children — even a few adult-strength iron tablets can be fatal. Keep iron supplements away from children. Chronic iron overload from excess supplementation, repeated transfusions, or hereditary hemochromatosis damages the liver, heart, and pancreas. Healthy adult men and postmenopausal women rarely need iron supplements and should not take them without testing for deficiency first.

Who should be cautious

Men and postmenopausal women should not take iron without documented deficiency. People with hereditary hemochromatosis or other iron-overload conditions must avoid iron supplements. Pregnant women generally need supplementation, but should use prenatal-prescribed doses. Keep all iron away from young children.

Interactions

Iron reduces absorption of levothyroxine, bisphosphonates, certain antibiotics (tetracyclines, quinolones), and levodopa — separate by at least 2 hours. Calcium and zinc supplements taken at the same meal reduce iron absorption. Antacids and proton pump inhibitors reduce iron absorption significantly. Vitamin C taken with iron substantially boosts absorption.

Frequently asked questions

Should I take iron supplements?⌄

Only if you have a documented deficiency or are at high risk (pregnancy, heavy menstrual bleeding, vegetarian/vegan diet with low intake). Men and postmenopausal women should not take iron routinely.

How can I make iron easier on my stomach?⌄

Try taking with a small meal, switch to bisglycinate or carbonyl iron, or try alternate-day dosing. Lower elemental doses (such as 25 mg) are often better tolerated and may absorb as well as higher doses overall.

Should I take iron with vitamin C?⌄

Yes, especially for non-heme iron and supplements. Vitamin C can multiply absorption. A glass of orange juice or a 250 mg vitamin C tablet works well.

Why does iron make stools dark?⌄

Unabsorbed iron interacts with sulfide in the gut to produce dark or black stools. This is harmless but can mask the appearance of gastrointestinal bleeding — tell your doctor if asked about stool color.

How long until iron supplements work?⌄

Hemoglobin begins to rise within 2 to 4 weeks. Full replenishment of iron stores (ferritin) takes 3 to 6 months of consistent dosing.

References

NIH ODS Iron Fact Sheet — NIH Office of Dietary Supplements link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.