Quick answer

Women aged 19 to 50 need 18 mg of iron a day, more than twice the 8 mg men need, because menstruation adds to iron losses. Pregnancy raises the need to 27 mg, and from age 51 it drops to 8 mg. Women eat 12.6 to 13.5 mg a day on average.^1,2

Key facts

Counting supplements, women's average iron intake rises to 17.0 to 18.9 mg a day.²
Multivitamins made for women typically provide 18 mg of iron, 100% of the Daily Value.²
Pregnant women need 27 mg of iron a day, but their median intake from food is 14.7 mg.²
A ferritin blood test shows whether iron stores are low before you start a supplement.²

Why women need more iron than men

People lose only small amounts of iron each day in urine, stool, sweat and shed skin cells. Losses are greater in women who menstruate because of blood loss.²

Most people in the US get enough iron from food. Average intake from food is 16.3 to 18.2 mg a day for men and 12.6 to 13.5 mg for women, and supplements bring women's average to 17.0 to 18.9 mg.^1,2

The gap is widest from the teens to 50. Teen girls need 15 mg against 11 mg for teen boys, and women aged 19 to 50 need 18 mg against 8 mg for men; after 50 the two recommendations are the same.²

What iron did for women in trials

Most trials of iron in women enrolled women who menstruate, and the trials on tiredness enrolled only women or adults whose iron stores were already low. Each claim below shows its grade and the amounts used.^3,4

Helps women who menstruate build hemoglobin and iron stores*^1,2,3

Strong evidence

A Cochrane review of 67 randomized trials in 8,506 women who menstruate found that daily iron raised hemoglobin (51 trials, 6,861 women, high-quality evidence) and iron stores, and made low iron less common. Women aged 19 to 50 need 18 mg a day, against 8 mg for men, because menstruation adds to their iron losses. Iron also roughly doubled reports of stomach and bowel side effects in these trials.

Amount studied: Daily iron tablets taken at least five days a week; the amount varied between trials

May lessen tiredness in adults whose iron stores are low but whose hemoglobin is normal*^3,4,5

Moderate evidence

A review of randomized trials in adults with low iron stores and normal hemoglobin found that iron reduced self-reported tiredness (4 trials, 714 people) but did not change measured exercise capacity. In one trial, 198 tired women with ferritin below 50 mcg/L took 80 mg of iron a day as ferrous sulfate or a placebo for 12 weeks, and their fatigue scores fell 47.7% with iron against 28.8% with placebo. The effect is modest and rests on self-report.

Amount studied: 80 mg a day as ferrous sulfate for 12 weeks in one trial; amounts varied in the others

May improve endurance exercise capacity in women who menstruate, mainly when their iron is low*^3,4,6,7

Moderate evidence

A meta-analysis of 22 randomized trials in women of reproductive age found that daily iron raised maximal oxygen uptake by 2.35 mL per kg per minute and lowered heart rate at set workloads, and a Cochrane review reached the same conclusion. Only 3 of those trials were judged to have a low likelihood of bias, and in adults whose hemoglobin was normal, iron did not change measured exercise capacity. NIH describes the results as conflicting, and sports nutrition groups advise iron for performance only when iron is depleted.

Amount studied: Daily oral iron, in amounts and for lengths of time that varied between trials

Check your iron before adding a supplement

Serum ferritin, a measure of the body's iron stores, is the most efficient and least costly test for low iron. A level below 30 mcg/L suggests low iron, though other factors can push ferritin up.²

Hemoglobin, the usual screening test, is neither sensitive nor specific for low iron, and it often stays normal while stores run down. Ferritin falls first, which is why it can pick up low stores earlier. Ask for it if you are often tired, train hard or eat no meat.²

Pregnancy, breastfeeding and after 50

Pregnant women need 27 mg of iron a day. Breastfeeding women need 9 mg, or 10 mg if they are 18 or younger.^1,2

In pregnancy the volume of blood expands, so the need rises by half. US dietary guidance asks pregnant women to take an iron supplement when their obstetrician or other provider recommends one, and medical groups differ on whether every pregnant woman should be screened and given iron.²

Multivitamins made for men or older adults often contain less iron or none.²

In a study of 1,106 adults aged 67 to 96, 13% had high iron stores, and only 1% of those were explained by long-term illness.²

From 51, women need no more iron than men. For most women over 50, 60 or 70, a multivitamin with little or no iron matches that need better than one made for younger women.^1,2

Heavy periods, pregnancy and other cautions

Heavy menstrual bleeding is one of the main reasons women run low on iron. At least 10% of women who menstruate are thought to have it, and limited evidence suggests it accounts for a third or more of iron deficiency anemia in women of reproductive age. If your periods are heavy, see a doctor about the cause as well as the iron.²

In pregnancy, a Cochrane review found that daily iron of 9 to 90 mg cut anemia at term by 70% and iron deficiency at term by 57%. Set your iron with your prenatal care provider rather than adding a separate product on your own.²

In trials in women, iron made both hard stools and loose stools about twice as common. The side effects guide covers ways to make them less likely.³

Ask first if you are pregnant or planning a pregnancy
Ask first if your periods are heavy, so the cause can be checked
Ask first if you take levothyroxine, an antibiotic or a medicine for acid reflux¹
Ask first if you are past menopause and no one has told you that you need iron

Questions people ask

Should women over 50 take iron?

Usually not without a reason. From 51, women need 8 mg a day, the same as men, and multivitamins for older adults often leave iron out. In one study of adults aged 67 to 96, high iron stores were more common than low ones.^1,2

Do women who exercise need more iron?

Possibly. People who train hard may need 30% to 70% more iron, and athletes lose some in sweat. Sports nutrition groups recommend iron for performance only when a test shows it is depleted.⁷

Is iron safe in early pregnancy?

The American College of Obstetricians and Gynecologists recommends low-dose iron starting in the first trimester, while the US Preventive Services Task Force found too little evidence to recommend routine iron for every pregnant woman without symptoms. Follow your prenatal provider's advice.²

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.