Short answer. Children aged 1 to 13 need 7 to 10 mg of iron a day, men need 8 mg and women aged 19 to 50 need 18 mg, according to the NIH Office of Dietary Supplements. The upper limit is 40 mg a day through age 13 and 45 mg for teens and adults. A ferritin test shows whether stores are low.
Iron sources and supplement forms at a glance
| Source or form | What the research shows | What to know |
|---|---|---|
| Heme iron (meat, seafood, poultry) | Better absorbed than nonheme iron and less affected by the rest of the meal | About 10% to 15% of the iron people eat in western diets |
| Nonheme iron (plants, fortified grains) | Absorption rises with vitamin C and meat, falls with phytate and some polyphenols | About half of US dietary iron comes from bread, cereal and other grain products |
| Ferrous salts (sulfate, gluconate, fumarate) | The most studied forms; ferrous iron is absorbed better than ferric iron | At 45 mg a day or more, nausea and constipation are more common |
| Ferrous bisglycinate (amino acid chelate) | 25 mg kept iron stores as well as 50 mg of ferrous sulfate in 80 pregnant women, with fewer stomach complaints | Chelates and heme iron polypeptides might cause fewer stomach side effects than salts |
| Every form | The label lists elemental iron, the amount of the mineral itself, so no conversion is needed (NIH ODS) | |
Source: NIH Office of Dietary Supplements; Milman 2014 (PMID 24152889).
What does iron do in the body?
Iron is part of hemoglobin, the protein in red blood cells that carries oxygen from the lungs to the tissues. It is also part of myoglobin, which supplies oxygen to muscle, and it is needed for physical growth, neurological development, normal cell function and the making of some hormones (NIH Office of Dietary Supplements).
An adult body holds 3 to 4 grams of iron, most of it in hemoglobin. Much of the rest is stored as ferritin in the liver, spleen and bone marrow. The body loses only small amounts each day, more in women who menstruate. A liver hormone called hepcidin is the main regulator of how much iron the gut absorbs and where it goes (NIH Office of Dietary Supplements).
How much iron do children and adults need?
The Recommended Dietary Allowance (RDA) and the upper limit (UL) both cover food, drinks and supplements combined.
| Age | Boys and men | Girls and women | Upper limit |
|---|---|---|---|
| 0–6 months | 0.27 mg (Adequate Intake) | 0.27 mg (Adequate Intake) | 40 mg |
| 7–12 months | 11 mg | 11 mg | 40 mg |
| 1–3 years | 7 mg | 7 mg | 40 mg |
| 4–8 years | 10 mg | 10 mg | 40 mg |
| 9–13 years | 8 mg | 8 mg | 40 mg |
| 14–18 years | 11 mg | 15 mg | 45 mg |
| 19–50 years | 8 mg | 18 mg | 45 mg |
| 51 years and older | 8 mg | 8 mg | 45 mg |
| Pregnancy | — | 27 mg | 45 mg |
| Lactation | — | 10 mg (14–18), 9 mg (19–50) | 45 mg |
Source: NIH Office of Dietary Supplements.
People who eat no meat need 1.8 times these amounts, because iron from plants is absorbed less well and meat itself helps nonheme iron absorption. The Daily Value on labels is 18 mg for adults and children 4 and older. Doctors sometimes prescribe more than the upper limit for a set time to rebuild stores; that is a decision for the doctor, and a child's dose belongs with the pediatrician (NIH Office of Dietary Supplements).
Iron in common foods
| Food and serving | Iron, mg |
|---|---|
| Breakfast cereal fortified with 100% of the DV, 1 serving | 18 |
| Oysters, cooked, 3 ounces | 8 |
| White beans, canned, 1 cup | 8 |
| Beef liver, pan fried, 3 ounces | 5 |
| Lentils, boiled, ½ cup | 3 |
| Tofu, firm, ½ cup | 3 |
| Beef, bottom round, 3 ounces | 2 |
| Chickpeas, boiled, ½ cup | 2 |
| Egg, 1 large | 1 |
Source: NIH Office of Dietary Supplements.
The body absorbs about 14% to 18% of the iron in mixed diets that include meat, seafood and vitamin C, and 5% to 12% from vegetarian diets. Breast milk iron is well absorbed but is not enough after about 4 to 6 months, which is why infant formulas are fortified with 12 mg per liter (NIH Office of Dietary Supplements).
Who is most likely to run low on iron?
Most people in the US get enough iron from food. The NIH lists these groups as most likely to fall short:
- Infants and toddlers. Full-term babies usually have enough stored iron for 4 to 6 months, then need iron-rich solid foods or fortified formula. About 18% of infants aged 6 to 12 months have low intakes, and 8% of toddlers are iron deficient.
- Teenage girls and women who menstruate, especially with heavy periods.
- Pregnant women. In national data from 1999 to 2006, 18% were iron deficient: 6.9% in the first trimester and 29.7% in the third.
- Frequent blood donors. About 25% to 35% of regular donors develop iron deficiency. In a US trial of 215 donors, 67% of those who took no iron had not rebuilt their stores 168 days after one donation; with a daily 37.5 mg iron tablet, the median was 76 days (Kiss 2015).
- People with certain digestive disorders or past stomach or bowel surgery, which can limit absorption.
Tiredness, weakness, trouble concentrating and feeling cold can come with low iron, but none of them is specific (NIH Office of Dietary Supplements). They are reasons to ask for a blood test, not to start iron on your own.
What blood test shows low iron stores?
Hemoglobin and hematocrit are the usual screening tests, but they change late. Iron runs out in stages: stores fall first, then the supply to new red cells, and only then does hemoglobin drop. Serum ferritin falls in the first stage, which makes it the most efficient test for spotting low stores early. A ferritin below 30 mcg/L suggests iron deficiency. Inflammation and infection can push ferritin up, so doctors often combine several tests (NIH Office of Dietary Supplements).
How should you take iron so it absorbs?
Controlled trials in young women with low iron stores, using labeled iron to measure absorption directly, give practical answers.
- Bigger doses absorb less efficiently. In 54 women with low ferritin, raising the dose sixfold, from 40 to 240 mg, only tripled the iron absorbed, from 6.7 to 18.1 mg. Doses of 60 mg or more raised hepcidin for a day and cut absorption from the next day's dose by 35% to 45% (Moretti 2015).
- Every other day can beat every day. In 40 women, 60 mg taken on alternate days for 28 days delivered 175.3 mg of absorbed iron, versus 131.0 mg from the same number of doses taken daily for 14 days. Splitting a dose in two did not help and raised hepcidin (Stoffel 2017).
- Over six months, alternate days were gentler. In a double-masked trial of 150 women given the same total amount, ferritin ended up the same with either schedule, but stomach side effects were 1.56 times as common with daily dosing, and fewer women were iron deficient at 6 months with alternate days (3.0% versus 11.4%) (von Siebenthal, eClinicalMedicine 2023).
- Coffee and breakfast get in the way; vitamin C helps. In 34 women, taking 100 mg of iron with 80 mg of vitamin C raised absorption by 30%, and 500 mg added nothing more. Coffee cut absorption by 54%, and a breakfast with coffee and orange juice by 66% (von Siebenthal, Am J Hematol 2023).
These doses are far above what a multivitamin carries, so the findings matter most when a doctor has advised iron. Taking iron with food can ease stomach upset, even though it lowers absorption (NIH Office of Dietary Supplements). Experts also suggest taking calcium and iron supplements at different times of day.
Which form of iron is best tolerated?
Ferrous and ferric salts are the most common forms. Ferrous iron dissolves better, so it is absorbed better than ferric iron. Heme iron polypeptides, carbonyl iron, iron amino acid chelates and polysaccharide-iron complexes might cause fewer stomach side effects than the salts (NIH Office of Dietary Supplements).
The clearest head-to-head trial: 80 healthy pregnant women in Denmark took either 25 mg of iron as ferrous bisglycinate or 50 mg as ferrous sulfate from mid-pregnancy to delivery. Low ferritin was equally uncommon in both groups, and stomach complaints were less frequent with bisglycinate (Milman 2014).
Can you take too much iron?
Yes. From food the risk is low for adults with normal digestion, but high-dose supplements cause stomach upset, constipation, nausea, abdominal pain, vomiting and diarrhea, and supplements with 25 mg or more can lower zinc absorption (NIH Office of Dietary Supplements).
Iron supplements are a real poisoning risk for young children. Between 1983 and 2000, at least 43 US children died after swallowing iron supplements. Every solid iron supplement must carry an FDA warning that accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. Keep the bottle out of children's reach and call a doctor or poison control right away if a child swallows any (NIH Office of Dietary Supplements).
Some people absorb too much iron from food because of an inherited HFE gene change. About 1 in 10 White people carry the most common variant, and about 4.4 in 1,000 have two copies (NIH Office of Dietary Supplements). This is one more reason to check iron status before starting iron.
Does iron interact with medicines?
The NIH lists these:
- Levothyroxine (Synthroid, Levoxyl, Tirosint, Unithroid). Iron can reduce its absorption; the labels advise not taking levothyroxine within 4 hours of an iron supplement.
- Levodopa (Sinemet, Stalevo). Iron supplements can reduce how much levodopa the body absorbs.
- Proton pump inhibitors, such as lansoprazole and omeprazole. Lower stomach acid reduces nonheme iron absorption, and people low in iron who take these drugs may respond less well to iron supplements.
Anyone who takes these medicines regularly should talk with their prescriber about iron status and timing.
Which ASDHelp products contain iron?
Doses are copied from each label (elemental iron). The asdhelp.com catalog has no high-dose iron-only supplement; these products carry small amounts, all below the 40 mg upper limit for children, even at the highest label use.
- Spectrum Formula Chewable + Iron: 3 mg per 4 chewable tablets, as ferric glycinate, inside a multivitamin that also carries 250 mg of vitamin C per 4 tablets. Label directions: children 1 to 3 years, one to two tablets twice daily; 4 years or more, two to four tablets twice daily. The highest label use, 8 tablets, gives 6 mg of iron.
- Beef Organs: 3 mg per 6 capsules, from a blend of bovine liver (1 g), heart, kidney, pancreas and spleen. Label directions: 6 capsules a day; no children's dose. Liver is also a concentrated source of preformed vitamin A.
- InflamaCare Gut Amino Protein Strawberry: 5 mg per 2 scoops (51.8 g), in a rice protein powder with L-glutamine. Label directions: 2 scoops once a day; no children's dose.
- GI Binder Detox: 2 mg per 2 capsules, with zeolite clay and activated charcoal. Label directions: 2 capsules between meals; no children's dose.
Add up the iron from every product and fortified food and compare it with the limit for each person's age.
Questions to take to your doctor
- Is a ferritin test, together with a blood count, worth doing given our diet, periods, growth spurts or blood donation?
- If iron is advised, what dose, which form and for how long, and would every other day suit us better than daily?
- How much iron do all of our current supplements and fortified foods add up to, compared with the upper limit for each person's age?
- Do any of our medicines, such as levothyroxine, levodopa or an acid-reducing drug, call for separate timing?
Sources
- NIH Office of Dietary Supplements. Iron fact sheet for health professionals. ods.od.nih.gov
- National Academies. Dietary Reference Intakes tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Moretti D et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood 2015. PMID 26289639
- Stoffel NU et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women. Lancet Haematol 2017. PMID 29032957
- von Siebenthal HK et al. Alternate day versus consecutive day oral iron supplementation in iron-depleted women. eClinicalMedicine 2023. PMID 38021373
- von Siebenthal HK et al. Effect of dietary factors and time of day on iron absorption from oral iron supplements in iron deficient women. Am J Hematol 2023. PMID 37357807
- Milman N et al. Ferrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy in a randomized trial. J Perinat Med 2014. PMID 24152889
- Kiss JE et al. Oral iron supplementation after blood donation: a randomized clinical trial. JAMA 2015. PMID 25668261
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.