Iron
Iron is an essential trace mineral required for hemoglobin, myoglobin, oxygen transport, energy metabolism, and neurologic development.
Overview
Biological role
Iron is required for hemoglobin and myoglobin and supports oxygen transport, electron transport, oxidative metabolism, and many enzymes.
Mechanism of action
Iron cycles between ferrous and ferric states, allowing oxygen binding and electron transfer. Hepcidin regulates intestinal absorption and iron release from stores.
Chemical forms
Dietary heme iron and nonheme iron; supplement forms include ferrous sulfate, ferrous gluconate, ferrous fumarate, and other iron salts.
Quick answers before choosing a supplement
Chemical forms and absorption
Common forms
Dietary heme iron and nonheme iron; supplement forms include ferrous sulfate, ferrous gluconate, ferrous fumarate, and other iron salts.
Absorption context
Vitamin C enhances nonheme iron absorption. Calcium, phytates, polyphenols, tea, coffee, and some high-fiber foods can reduce nonheme iron absorption when consumed together.
Clinical use
Iron status should be interpreted with ferritin, transferrin saturation, inflammation markers, and clinical context when possible.
Absorption and action pathway
What to take with, and what to avoid
Works Well With
Avoid / Use Caution
Best time to take
Frequently asked questions
When is the best time to take Iron?
Use with meals if the supplement irritates the stomach; separate from medicines or competing minerals when needed.
Can Iron be taken with coffee or milk?
Some minerals compete with foods, drinks, or medicines. Separate timing is useful when treating a deficiency.
Who should be careful with Iron?
Higher-risk groups include pregnant people, infants and young children, menstruating people, frequent blood donors, people with gastrointestinal blood loss, and people with malabsorption.
Food and Intake
| Age / group | Male | Female | Pregnancy | Lactation | Upper limit |
|---|---|---|---|---|---|
| 1-3 years | 7 | 7 | – | – | UL 40 |
| 4-8 years | 10 | 10 | – | – | UL 40 |
| 9-13 years | 8 | 8 | – | – | UL 40 |
| 14-18 years | 11 | 15 | 27 | 10 | UL 45 |
| 19-50 years | 8 | 18 | 27 | 9 | UL 45 |
| 51+ years | 8 | 8 | – | – | UL 45 |
International reference intake comparison
| Country / authority | Common reference value |
|---|---|
| USA / NIH-FNB | RDA 8 mg men; 18 mg women 19-50; pregnancy 27; UL 45 |
| Europe / EFSA | PRI about 11 mg men/womenpostmenopause and 16 mg womenpremenopause |
| Australia-New Zealand / NRV | RDI 8 mg men; 18 mg women; pregnancy 27 |
| Thailand / Thai FDA | Thailand: use Thai RDI and Thai FDA / Ministry of Public Health regulations for labeling and supplement products. Do not interpret labeling values as therapeutic doses; product-specific limits must be checked against the latest notification and formula. |
This table compares reference-intake frameworks across authorities. Values may use different terms such as RDA, AI, PRI, or NRV and should not be merged into one universal dose.
Food source comparison for Iron
| Food | Serving amount | Iron | %DV | %DV bar | Servings to reach 18 mg |
|---|---|---|---|---|---|
| iron-fortified cereal | 1 serving | 18 mg | 100% | 1.0 | |
| oysters | 3 oz | 8 mg | 44% | 2 | |
| white beans | 1 cup | 8 mg | 44% | 2 | |
| lentils | 1 cup | 6.6 mg | 37% | 3 | |
| cooked spinach | 1/2 cup | 3.2 mg | 18% | 6 | |
| beef | 3 oz | 2.2 mg | 12% | 8 |
Food values are practical comparison values. Actual content varies by variety, preparation, fortification, and serving size.
Safety
Deficiency
Deficiency can progress from depleted iron stores to iron-deficiency erythropoiesis and iron-deficiency anemia, with fatigue, weakness, impaired work capacity, and developmental effects in children.
Excess and toxicity
High iron intake can cause gastrointestinal symptoms and iron overload. Accidental ingestion of iron supplements can be fatal in children.
Precautions
Iron supplements should be used when deficiency risk, laboratory evidence, pregnancy needs, or clinical indication supports use. People with hemochromatosis should avoid iron supplements unless prescribed.
Special populations
Higher-risk groups include pregnant people, infants and young children, menstruating people, frequent blood donors, people with gastrointestinal blood loss, and people with malabsorption.
Fast risk map
LOW: insufficient intake
Deficiency can progress from depleted iron stores to iron-deficiency erythropoiesis and iron-deficiency anemia, with fatigue, weakness, impaired work capacity, and developmental effects in children.
UL: excess intake
High iron intake can cause gastrointestinal symptoms and iron overload. Accidental ingestion of iron supplements can be fatal in children.
Precautions: interactions and timing
Iron supplements should be used when deficiency risk, laboratory evidence, pregnancy needs, or clinical indication supports use. People with hemochromatosis should avoid iron supplements unless prescribed.
SP: special populations
Higher-risk groups include pregnant people, infants and young children, menstruating people, frequent blood donors, people with gastrointestinal blood loss, and people with malabsorption.
Interactions and Clinical Context
Drug interactions
ODS lists interactions with levodopa, levothyroxine, proton pump inhibitors, and some antibiotics. Iron can reduce absorption of some medicines when taken at the same time.
Food interactions
Vitamin C enhances nonheme iron absorption. Calcium, phytates, polyphenols, tea, coffee, and some high-fiber foods can reduce nonheme iron absorption when consumed together.
Clinical notes
Iron status should be interpreted with ferritin, transferrin saturation, inflammation markers, and clinical context when possible.
Evidence level
High for essentiality, deficiency anemia, RDA, UL, and drug/food interaction precautions.