Iron: Roles, Food Sources, Deficiency, Excess and Supplement Safety
What iron does, food sources, who is at risk of low iron, official intake levels, what trials show for supplements, side effects, excess, medicine timing and child safety.
Content last updated . This page has not been medically reviewed.
What is Iron good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Oxygen carrying in red blood cells
Established roleIron is needed to make haemoglobin, the protein in red blood cells that carries oxygen around the body.
Supplements: Supplements correct low iron; no good evidence of extra benefit when iron levels are adequate.
Red blood cell formation
Established roleIron is important for making red blood cells. Without enough, the body can develop iron deficiency anaemia.
Supplements: Supplements correct low iron; no good evidence of extra benefit when iron levels are adequate.
Oxygen supply to muscles
Established roleIron is part of myoglobin, which supplies oxygen to muscles.
Supplements: Supplements correct low iron; no good evidence of extra benefit when iron levels are adequate.
Prevention of iron deficiency anaemia
Clinically supportedGetting enough iron from food prevents iron deficiency anaemia, the most common type of anaemia. Iron tablets are used for about 6 months when a blood test shows it.
Supplements: Iron tablets treat diagnosed iron deficiency anaemia under clinician guidance.
Present in every cell
Established roleIron is an essential mineral found in every cell, and the body cannot make it, so it must come from food.
Supplements: Supplements correct low iron; no good evidence of extra benefit when iron levels are adequate.
Energy and tiredness when iron is low
Deficiency linkTiredness and low energy are common signs of iron deficiency anaemia. Correcting low iron can relieve this tiredness.
Supplements: Helps only when tiredness is caused by low iron; not shown to raise energy when iron is adequate.
Needs during pregnancy
Deficiency linkIron deficiency is a common cause of anaemia in pregnancy, and untreated anaemia can raise the risk of complications before and after birth.
Supplements: Amounts and products are a clinician's decision.
Link with restless legs syndrome
Preliminary or mixedThe NHS says restless legs syndrome is thought to be tied to iron and dopamine levels, and iron supplements may be needed if blood iron is low.
Supplements: Considered only when blood iron is low.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (2)
- Reduce FatigueDeficiency link
Low iron over a long time can cause iron deficiency anaemia, which often shows as tiredness and low energy. Iron corrects tiredness that is caused by low iron; there is no good evidence in the sources we read that extra iron raises energy when iron levels are normal.
- Women’s WellnessDeficiency link
Heavy periods and pregnancy are very common causes of iron deficiency anaemia, so women are more often affected. Needs are set separately for women aged 19 to 49 by the NHS.
Body systems (8)
- Energy & FatigueDeficiency link
Iron makes haemoglobin, which carries oxygen in the blood. Low iron can cause tiredness and low energy; extra iron has not been shown to help when levels are adequate.
- Bones, Joints & MusclesEstablished role
Iron is part of myoglobin, which supplies oxygen to muscles. In haemochromatosis, excess iron can also affect the joints.
- Cardiovascular SystemDocumented risk
Untreated iron overload in haemochromatosis can damage the heart.
- Heart & CirculationDocumented risk
Untreated iron overload in haemochromatosis can damage the heart. Iron also takes part in carrying oxygen around the body.
- Hepatic / Liver SystemDocumented risk
In haemochromatosis, iron slowly builds up and can damage the liver. This is an inherited condition, not a result of normal food intake.
- Musculoskeletal SystemEstablished role
Iron is part of myoglobin, which supplies oxygen to muscle; iron overload can affect joints.
- Endocrine SystemDocumented risk
Iron overload in haemochromatosis can damage the pancreas.
- Nervous SystemPreliminary or mixed
The NHS says restless legs syndrome is thought to be tied to iron and dopamine levels, and lists iron deficiency anaemia among linked conditions. The link is a suspected one.
Body parts (7)
- CellsEstablished role
Iron is an essential mineral found in every cell of the body, and the body cannot make it.
- HeartDocumented risk
Untreated iron build-up in haemochromatosis can damage the heart.
- JointsDocumented risk
Untreated iron build-up in haemochromatosis can damage the joints and cause joint pain.
- LiverDocumented risk
Too much iron in haemochromatosis builds up and can damage the liver.
- MusclesEstablished role
Iron is part of myoglobin, the protein that supplies oxygen to muscles.
- PancreasDocumented risk
Untreated iron build-up in haemochromatosis can damage the pancreas.
- HairDeficiency link
Hair loss is listed by the NHS as a less common sign of iron deficiency anaemia. It does not show that extra iron helps hair when iron is adequate.
Root causes (2)
- Nutrient DeficiencyDeficiency link
Not getting or absorbing enough iron, or losing it through bleeding, can lead to iron deficiency anaemia.
- Poor DietDeficiency link
The NHS says diet can be a cause of iron deficiency anaemia in some cases, and in pregnancy it is most often too little iron in the diet.
Habits (2)
- Balanced NutritionEstablished role
Iron comes from food. Animal iron is absorbed more easily than plant iron, vitamin C foods help absorption and black tea reduces it. Most people can meet needs from a varied diet.
- ExerciseDeficiency link
MedlinePlus lists long-distance runners among people at higher risk of low iron.
Biomarkers (1)
- HemoglobinEstablished role
Iron is needed to make haemoglobin. A full blood count is the test a GP uses to diagnose iron deficiency anaemia.
Conditions & symptoms (6)
- HemochromatosisDocumented risk
An inherited condition where too much iron builds up and can damage the liver, joints, pancreas and heart; iron supplements are usually avoided.
- Iron DeficiencyDeficiency link
Low iron from poor intake, poor absorption or blood loss; heavy periods and pregnancy are common causes.
- Iron Deficiency AnemiaDeficiency link
Long-term low iron leads to iron deficiency anaemia, with tiredness, breathlessness and pale skin.
- Iron OverloadDocumented risk
Slow build-up of iron over many years can damage organs.
- Restless Legs SyndromePreliminary or mixed
Thought to be tied to iron and dopamine levels; iron supplements may be needed if blood iron is low.
- Pica DiseaseDeficiency link
Craving non-food items such as ice or paper is listed as a less common sign of iron deficiency anaemia.
Documented risks and interactions (2)
- Risk of too much iron (haemochromatosis). In haemochromatosis the body absorbs too much iron, which builds up and can damage the liver, joints, pancreas and heart. People with it are usually told to avoid iron and vitamin C supplements.
- Iron overdose and children. Very high doses of iron can be fatal, particularly for children, so iron supplements must be kept out of their reach. Poisoning symptoms include nausea, vomiting, dizziness and grey skin.
Safety first: iron and children
Iron overdose is particularly dangerous for children, and a severe overdose can happen if a child eats adult multivitamins such as prenatal vitamins. [1] If a child (or anyone) may have swallowed iron, do not wait for symptoms. In the US call 911 or Poison Help at 1-800-222-1222. [1] Outside the US see Poison help by country. The NHS says very high doses of iron can be fatal, particularly if taken by children, so supplements should be kept out of reach. [2] More is on Iron overdose and child safety.What iron is and what it does
Iron is an essential mineral found in every cell. The body needs it to make hemoglobin (the oxygen-carrying protein in red blood cells) and myoglobin (in muscle), and it cannot make iron itself. [3] A low iron level over a long period can lead to iron deficiency anemia. [3] Iron is also a nutrient where more is not always better: in hemochromatosis the body absorbs more iron than it needs, and the extra is stored in the liver, heart and pancreas, where it can damage organs. [4]How to read the labels on this page: established role / deficiency treatment means standard care backed by strong evidence; promising but limited means some trials with caveats; insufficient or Proper evidence not found means we looked and could not support a claim.
Food sources
MedlinePlus lists dried beans, dried fruits, eggs, iron-fortified cereals, liver, lean red meat, oysters, poultry, salmon, tuna and whole grains among the best sources. It adds that iron from vegetables, fruits, grains and supplements is harder for the body to absorb. [3] The NHS (UK) also lists nuts and soy bean flour, and says to avoid liver during pregnancy. [2] Details are on Foods high in iron; the difference between animal and plant iron is on Heme vs nonheme iron.Official intake levels
Reference values differ by country, and they describe what is enough for most healthy people, not a target to exceed. The figures below are in mg of iron per day as the sources state them; the pages we read do not discuss supplement salt weights.| Source and year | Population | Value |
|---|---|---|
| NHS (UK), page reviewed 2020 | Men 19+ and women 50+ | 8.7 mg a day [2] |
| NHS (UK), 2020 | Women 19 to 49 | 14.8 mg a day [2] |
| US Dietary Reference Intakes (RDA), as listed by MedlinePlus, 2025 | Men 19+; women 51+ | 8 mg a day [3] |
| US RDA via MedlinePlus, 2025 | Women 19 to 50 | 18 mg a day [3] |
| US RDA via MedlinePlus, 2025 | Pregnant women, all ages | 27 mg a day [3] |
| US RDA via MedlinePlus, 2025 | Breastfeeding women 19 to 50 (14 to 18) | 9 mg a day (10 mg a day) [3] |
The NHS says taking 17 mg or less a day of iron supplements is unlikely to cause harm, and that side effects such as constipation, nausea, vomiting and stomach pain can occur with high doses over 20 mg. [2] We could not read the NIH Office of Dietary Supplements or EFSA pages (access was refused), so we do not state a US or EU upper limit here. See RDA, AI, DV and UL for what these terms mean.
Who may need assessment
The NHS names heavy periods and pregnancy as very common causes of iron deficiency anemia, and bleeding in the stomach and intestines as another common cause. [5] MedlinePlus also lists frequent blood donors, long-distance runners, and people with conditions that make it hard to absorb nutrients. [3] Tiredness, breathlessness and pale skin are not specific, so they cannot confirm low iron on their own, and a clinician usually starts with a blood test. [5] See Iron deficiency and iron-deficiency anemia, Iron tests explained and Anemia and iron deficiency.What the evidence shows for supplements
| Question | What the source found | Strength |
|---|---|---|
| Iron deficiency anemia | The NHS says that if the blood test shows a low red blood cell count, iron tablets will be recommended, usually for about 6 months. [5] | Established treatment (clinician-led) |
| Menstruating women, daily iron, mixed health status | A Cochrane review of 67 trials (8,506 women) found daily iron reduced anemia and iron deficiency, raised hemoglobin, improved exercise performance and appeared to reduce symptomatic fatigue, at the cost of more gastrointestinal side effects. [6] | Established for anemia; fatigue finding more limited |
| Iron-deficient adults without anemia | Self-reported fatigue was lower (standardized difference -0.38; 4 trials, 714 people) but objective physical capacity did not change. [7] | Promising but limited |
| People with normal iron stores | Proper evidence not found in the sources we read for a benefit. Hemochromatosis shows that excess can harm. [4] | Insufficient |
Absorption study (not a recommendation): in a small trial of 40 iron-depleted young women (ferritin 25 micrograms per liter or less) given iron as ferrous sulfate, alternate-day dosing gave higher fractional absorption than consecutive-day dosing (21.8% versus 16.3%). The authors said the findings should be confirmed in people with iron-deficiency anemia. [8] Absorption is not the same as a better health outcome.
Side effects
Common effects are constipation, diarrhea, stomach pain, heartburn, nausea and darker stools. [5] A meta-analysis of 43 trials found ferrous sulfate raised the odds of gastrointestinal side effects (odds ratio 2.32 versus placebo) and found no clear link to dose. [9] Details and when to seek care are on Iron supplement side effects.Forms and labels
Common iron supplement salts include ferrous sulfate, gluconate and fumarate. [1] Whether one form is better depends on the person and the question; see Iron forms compared. In the US, federal rules require solid iron supplements to carry a warning that accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. [10] Product quality is covered on Quality, testing and certifications.Medicines, pregnancy, kidney, liver and surgery
- Medicines. The NHS lists calcium and iron supplements among things that may not mix well with levothyroxine, and medicines or supplements containing iron or zinc among those that may not mix well with doxycycline. [11][12] Ask a pharmacist about timing and read How interactions work and Spacing supplements and medicines.
- Absorption. Black tea contains substances that bind dietary iron, while foods rich in vitamin C increase absorption. [3]
- Pregnancy. Needs are higher, but amounts and products are a clinician's decision; see Iron in pregnancy.
- Hemochromatosis or liver disease. The NHS says people being treated for hemochromatosis are usually advised to avoid iron or vitamin C supplements. [13] See Iron overload and hemochromatosis.
- Kidney disease and surgery. Proper evidence not found in the pages we read for general iron supplement rules in these situations (searched: NHS, MedlinePlus, NHLBI, NIDDK iron pages). Tell your surgeon and kidney team about every supplement; see Minerals and kidney disease and Supplements before surgery.
Practical points
- Do not start iron because of tiredness alone; ask for a test first.
- If a clinician has found you have enough iron, extra is not a general wellness step.
- Store all iron products locked away from children.
Frequently asked questions
Can I take iron without a blood test?
Symptoms of low iron overlap with many other conditions. The NHS describes a blood test as what a GP usually does first, and treatment follows once the cause is found. [5]
Does vitamin C help iron absorption?
MedlinePlus says foods rich in vitamin C increase iron absorption, and the NHS says drinking orange juice after an iron tablet may help absorption. [3][5]
What is too much iron?
The NHS says doses over 20 mg a day can cause stomach side effects, while 17 mg or less a day is unlikely to cause harm. [2] We could not verify a US or EU upper limit from sources we could read.
Can iron supplements turn stools dark?
Yes. The NHS lists darker than usual poo as a possible side effect. [5] Black or tarry stools can also mean bleeding, so tell a clinician. [14]
Who should not take iron supplements unless prescribed?
People with hemochromatosis. MedlinePlus lists no iron supplements as part of its treatment. [3] Ask a clinician about any other condition.
References
- MedlinePlus (US National Library of Medicine). Iron overdose. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: Iron. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Iron in diet. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Hemochromatosis. Read 2026-10-23.
- NHS (UK). Iron deficiency anaemia. Page last reviewed 26 January 2024. Read 2026-10-23.
- Low et al. Daily iron supplementation for improving anaemia, iron status and health in menstruating women. Cochrane Database of Systematic Reviews. PubMed abstract read 2026-10-23.
- Houston et al. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. BMJ Open. PubMed abstract read 2026-10-23.
- Stoffel 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 Haematology. PubMed abstract read 2026-10-23.
- Tolkien et al. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One. PubMed abstract read 2026-10-23.
- US Code of Federal Regulations, 21 CFR 101.17(e): dietary supplements containing iron or iron salts (eCFR). Read 2026-10-23.
- NHS (UK). Levothyroxine (medicine page). Read 2026-10-23.
- NHS (UK). Doxycycline: how and when to take it. Read 2026-10-23.
- NHS (UK). Haemochromatosis. Page last reviewed 29 March 2023. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Black or tarry stools. Read 2026-10-23.