Iron

What does iron do?

Iron is the key component of the protein hemoglobin in red blood cells; hemoglobin carries oxygen from the lungs to the tissues. It is also found in the structure of myoglobin, which supplies oxygen in muscles, and supports muscle metabolism. It is also needed for physical growth, development of the nervous system, cell functions and the making of some hormones. ^[1]

An adult human has about 3–4 grams of iron; most of it is in hemoglobin. Most of the rest is stored in the liver, spleen and bone marrow as ferritin or hemosiderin, or is in myoglobin in muscles. The main protein carrying iron in the blood is transferrin. ^[1]

The fact that a mineral has a function in the body does not mean that taking more than an adequate amount will make it perform that function better. Replacing iron in a person with iron deficiency and supplement use by a person with full stores are different questions; for the second there is no proven benefit, and it carries risk.

What is the difference between heme and non-heme iron?

Iron in food comes in two forms. Plant foods and iron-fortified products contain only non-heme iron; meat, seafood and poultry contain both heme and non-heme iron. In a Western-type diet, about 10–15% of total iron intake is heme iron. ^[1]

Absorption of heme iron is higher and is less affected by other components of the meal. The NIH reports that iron absorption is about 14–18% in a mixed diet containing significant amounts of meat, seafood and vitamin C, and 5–12% in a vegetarian diet. Vitamin C (ascorbic acid) and meat, poultry and seafood increase the absorption of non-heme iron; phytate in grains and legumes and some plant polyphenols decrease it. Calcium can reduce the absorption of heme iron as well as non-heme iron. The NIH also states that in a typical Western-type diet these enhancing and inhibiting effects are weakened and affect iron status little in most people. ^[1]

How much iron is needed per day?

Reference values vary by organization. The values reported by the NIH from the US National Academies (NASEM) are RDAs set at a level that meets the needs of about 97–98% of healthy people. The European Food Safety Authority (EFSA), in its 2015 opinion, defines a population reference intake (PRI). ^{[1] [2]}

The age bands of the two organizations are not the same; the row heading is the NIH age band, and the age band to which the EFSA value belongs is written in parentheses. ^{[1] [2]}

The most marked difference between the two organizations is in pregnancy. While the NIH gives an RDA of 27 mg for pregnancy, EFSA, assuming that iron stores and increased absorption cover the extra need in pregnancy and breastfeeding, recommends the same value as for premenopausal women (16 mg). ^[2] The NIH also reports that the need is 1.8 times higher in people on a vegetarian diet because iron in plant foods is absorbed less. ^[1]

These values are the reference for the total amount healthy people should obtain from food; they are not the same as the amounts used in treating diagnosed iron deficiency. The NIH notes that, in iron deficiency anemia, physicians can at times prescribe amounts above the upper limit to fill the stores. ^[1]

Who is at higher risk of iron deficiency?

The main risk groups listed by the NIH are as follows: ^[1]

• Pregnant women: Plasma volume and red blood cell mass increase, and the need rises.
• Infants and young children: The stores of full-term infants generally last the first 4–6 months; in those who do not receive iron-rich complementary foods or iron-fortified formula, the risk of deficiency begins at 6–9 months. Preterm and low-birth-weight infants are at risk earlier.
• Women with heavy menstrual bleeding: Menorrhagia is thought to be present in at least 10% of women who menstruate; according to limited evidence, it may be responsible for 33–41% of cases of iron deficiency anemia in women of reproductive age.
• Frequent blood donors: Iron deficiency develops in 25–35% of regular donors.
• People with cancer, heart failure and digestive tract disease: Celiac disease, ulcerative colitis, Crohn’s disease, and stomach or intestinal surgery can reduce absorption or cause blood loss.

The 2021 guideline of the British Society of Gastroenterology (BSG) adds long-term acid-suppressing (PPI) use, long-term painkiller (NSAID) use and endurance athletes to this list. According to the guideline, menstrual bleeding is a common cause in premenopausal women; in men and postmenopausal women, iron deficiency anemia is often due to chronic blood loss from the digestive tract, and about one-third of these people have an underlying disease. Celiac disease is found in 3–5% of cases of iron deficiency anemia. ^[3]

What is the situation in Türkiye?

The Ministry of Health launched the “Demir Gibi Türkiye” (Strong as Iron Türkiye) program in April 2004. The program covers breastfeeding for the first 6 months, transition to suitable complementary foods at the end of the 6th month, free preventive iron support for every infant aged 4–12 months, and recommending iron treatment for anemic infants aged 13–24 months. The General Directorate of Public Health reports that the frequency of iron deficiency anemia in this age group fell from around 30% (a range of 12–80%) to 6.3%. ^[8] This program is for infants; the separate Ministry program for pregnant women and data on adult women in Türkiye are covered on the related subpages.

How is iron deficiency detected?

The NIH describes iron deficiency as progressing in three stages. In the first stage, only the stores decrease and serum ferritin falls. In the second stage, iron going to the bone marrow and transferrin saturation decrease, but hemoglobin is generally in the normal range. In the last stage, the stores are exhausted and hemoglobin and hematocrit fall; red blood cells become small and pale (microcytic, hypochromic). This last stage is iron deficiency anemia. ^[1]

Among the complaints due to iron deficiency anemia are weakness, fatigue, difficulty concentrating, digestive problems and impaired regulation of body temperature. Besides signs of anemia such as shortness of breath, the BSG guideline also lists findings more specific to iron deficiency: cracks at the corners of the mouth, tongue inflammation, spoon nails, restless legs syndrome and a craving to eat ice (pagophagia). ^{[1] [3]}

Symptoms do not establish a diagnosis on their own. The NIH describes measuring ferritin as the most effective and cost-efficient test for recognizing iron deficiency: ferritin below 30 µg/L suggests iron deficiency and below 10 µg/L suggests iron deficiency anemia. However, inflammatory conditions such as infection can raise ferritin. ^[1] BSG also regards ferritin as the most useful single test; it states that when ferritin is suspected of being misleadingly normal, tests such as transferrin saturation can help. ^[3]

How is iron deficiency anemia treated?

Treatment is planned by a physician and has two parts: replacing iron and finding the cause of the deficiency. The BSG 2021 guideline recommends that, unless colonoscopy is very soon, treatment not be postponed while investigations are awaited. As a first step the guideline recommends oral iron salts (ferrous sulfate, fumarate or gluconate); if not tolerated, it states that less frequent use, a different oral preparation or intravenous (parenteral) iron should be considered. Intravenous iron is recommended for situations in which oral iron cannot be used, is ineffective or is not tolerated, or when correction is urgent. ^[3]

The guideline also recommends monitoring the hemoglobin response in the first 4 weeks and continuing treatment for a while after hemoglobin returns to normal to fill the stores. Which preparation, in what amount and for how long is determined for the individual; this guide does not give a treatment schedule. ^[3]

Why is iron in pregnancy a separate topic?

In pregnancy, blood volume expands and iron requirement increases because of the needs of the baby and placenta. The NIH reports that iron deficiency in pregnancy increases the risk of maternal and infant death, preterm birth and low birth weight. ^[1]

The 2015 Cochrane review included 61 studies; 44 of them (43,274 women) contributed data comparing daily iron with no-iron support or placebo. Preventive iron support reduced maternal anemia at delivery by 70% (RR 0.30; 14 studies, 2,199 women, low-quality evidence) and iron deficiency at delivery by 57% (RR 0.43; 7 studies). The proportion of low-birth-weight infants was 8.4% in the iron group and 10.3% in the control group (RR 0.84; 0.69–1.03); differences in preterm birth and birth weight were not statistically significant. Women taking iron were also at higher risk of hemoglobin rising above 130 g/L in pregnancy. The authors state that support reduced the risk of maternal anemia and iron deficiency, and that its effect on other maternal and infant outcomes is less clear. ^[7]

The positions of organizations also differ: according to the NIH, the American College of Obstetricians and Gynecologists (ACOG) recommends low-dose iron supplementation starting in the first trimester, while the US Preventive Services Task Force (USPSTF) finds the evidence insufficient for routine screening and support in pregnant women without symptoms. ^[1] In Türkiye, the Ministry of Health’s Prenatal Care Management Guide (DOB, 2026) describes starting iron support from the 16th week of pregnancy in pregnant women without anemia and, in its flowchart (from the 4th month of pregnancy to the end of the 3rd month postpartum), 40–60 mg of elemental iron (Fe+2) per day for those with hemoglobin of 11 g/dL and above. ^[10] The Ministry program for pregnant women is covered separately on the anemia page.

Evidence table: claim, population and limits

The most useful distinction is to separate iron’s known functions from the measured results of supplements in specific groups. The summary below shows, for each claim, the group studied and the limit of the result.

What the results in the table have in common is that all were obtained in groups with iron deficiency or predisposed to anemia. That objective performance measures did not change in the fatigue meta-analysis shows that subjective benefit and physical capacity need to be evaluated separately. Data on school-age children come largely from countries where anemia and deficiency are common and cannot be directly carried over to a different setting such as Türkiye.

Is excess iron harmful?

In adults with normal gut function, the risk of iron overload from food is very low. High-dose supplements, however, can cause stomach upset, constipation, nausea, abdominal pain, vomiting and diarrhea. The upper limit (UL) reported by the NIH is 45 mg per day for ages 14 and over and 40 mg for infants and children up to age 13. These limits are for total iron from food and supplements and for healthy people (not a ceiling applied only to supplements, as with magnesium); supplements containing 25 mg or more of iron can also reduce zinc absorption. ^[1]

EFSA, in its 2024 opinion, could not establish a UL for iron. Based on studies in which no black stools were seen with 20–25 mg/day of supplements added to 15 mg/day of dietary intake, it defined a total “safe level of intake” of 40 mg per day for adults (including pregnant and breastfeeding women), and scaled it to children, deriving values between 10 mg/day at ages 1–3 and 35 mg/day at ages 15–17. EFSA states that a safe level of intake is to be interpreted more narrowly than a UL, because the intake at which the risk of an adverse effect begins to rise has not been defined. ^[9]

Taking more than 20 mg of iron per kilogram of body weight at once can cause corrosive damage to the gut, loss of fluid and blood, shock and organ failure; very high amounts can result in coma, seizures and death. In the US between 1983 and 1991, about one-third of child poisoning deaths were due to accidental ingestion of iron supplements. In the US, the label of supplements containing iron in solid form must carry a warning that accidental excess iron intake is one of the leading causes of fatal poisoning in children under 6. ^[1]

Hereditary hemochromatosis leads to excess iron accumulation in the body due to a change in the HFE gene. According to the NIH, about 1 in 10 white people carry the most common mutation, and 4.4 per thousand are homozygous for this mutation. If untreated, liver cirrhosis, liver cancer, heart disease and pancreatic dysfunction can develop. The American Association for the Study of Liver Diseases recommends avoiding iron and vitamin C supplements as part of treatment. ^[1] For this reason, iron use “for anemia” by a person with high ferritin can be harmful.

Which drugs does iron interact with?

The NIH’s interactions section gives three examples. Iron supplements can reduce the absorption of levodopa, used in Parkinson’s disease and restless legs syndrome. When taken together with the thyroid hormone levothyroxine, the effect of levothyroxine can drop in a clinically significant way in some patients; the label of some levothyroxine products states that levothyroxine should not be taken within 4 hours after an iron supplement. PPI drugs that suppress stomach acid can reduce the absorption of non-heme iron; use for up to 10 years has not been associated with iron depletion or anemia in people with normal iron stores, but PPI users with iron deficiency may respond inadequately to iron treatment. ^[1]

An interval needs to be left from some antibiotics (tetracycline and quinolone groups); antacids are also listed among the factors reducing iron absorption. These details are given with sources on the timing page. In people who use medications regularly, every iron-containing product is evaluated by a physician or pharmacist together with prescription drugs.

This guide does not recommend a daily or weekly personal dose. In a person in whom iron deficiency is suspected, making the diagnosis first and investigating the cause, and making the supplement decision according to these results, is the safest route.