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Iron

Iron is an essential mineral best known for allowing blood to carry oxygen between tissues. Except in case of deficiency, iron supplementation has no proven benefit; on the contrary, it can lead to iron poisoning.

Our evidence-based analysis on iron features 198 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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Summary of Iron

Primary information, health benefits, side effects, usage, and other important details

What is iron?

Iron is an essential dietary mineral present in a wide variety of foods. In its main role in the body, iron is a critical component of hemoglobin — the oxygen carrier of red blood cells — and a deficiency in iron leads to poor oxygen transport (anemia). In addition, iron acts as a cofactor for many enzymes. The iron found in plants (notably grains and legumes) is less bioavailable than the iron found in meat (in the form of heme). Iron is the double-edged sword of the nutrient world. On the one hand, many people have insufficient levels, but on the other hand, iron overload can be toxic to a wide variety of cells. Iron deficiency is the only reason to consider iron supplementation, though getting more iron through foods is preferable when possible. For people who already have enough iron, taking an iron supplement has no proven benefit, and on the contrary, it can lead to iron overdose.

What are the benefits of iron?

A lack of iron tends to produce fatigue, depression, impaired cognitive function, restless leg syndrome, and other adverse effects. Correction of an iron deficiency tends to improve symptoms, and even among people who aren't anemic, more than the bare minimum amount of iron may be needed to produce the optimal amounts of hemoglobin and reap the benefits of greater oxygen delivery; however, the beneficial effect is probably limited to people whose iron levels are low according to conventional standards, though more research is needed. Iron deficiency is fairly common, and a great number of factors negatively affect iron status, so iron supplementation and iron-rich diets can be expected to benefit many people.

What are the downsides of iron?

Supplementation can produce nausea, headaches, and other symptoms. As previously mentioned, iron overload is a serious health risk.

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How to Take

Recommended dosage, active amounts, other details

Make sure that you get the recommended daily allowance (RDA) for your gender, age, and situation:

  • 8 mg for men and nonmenstruating women

  • 15 mg for menstruating women 14–18 years old

  • 18 mg for menstruating women 19–50 years old

  • 27 mg for pregnant women

  • 10 mg for lactating women less than 18 years old

  • 9 mg for lactating women, 19–50 years old

Those numbers include the iron in your diet. Getting enough iron from foods makes supplementation unnecessary. Be careful not to ingest more iron than the daily tolerable upper intake level (UL) for your age, e.g., 45 mg for people older than 13.

For more details, see the Recommended Intake section below.

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Iron has on your body, how much evidence there is, and how strong these effects are.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-c Minor Very High See all 7 studies
In people without anemia, but who have iron deficiency or low ferritin levels, increasing iron stores through oral or intravenous supplementation can reduce fatigue somewhat. It's unclear if the average person with iron levels traditionally considered to be sufficient can benefit from increased iron intake in this regard, though what research we have suggests that it's unlikely.
grade-d Minor - See study
One study found a small increase in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
grade-d Minor - See study
One study found a small decrease in iron-deficient but non-anemic participants which wasn't statistically significant. This isn't a systematic assessment of studies.
grade-d Minor - See study
One study found a small increase in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
grade-d Minor Moderate See 2 studies
One study found a notable reduction in people with iron deficiency but not anemic, a small reduction in people with iron deficiency anemia, and ambiguous evidence in people without iron deficiency. The other study didn't find an effect. This isn't a systematic assessment of studies.
grade-d Minor - See study
There was a small improvement in one study of people with low iron levels but not anemia. This isn't a systematic assessment of studies.
grade-d Minor - See study
Both relative and absolute VO2max increased moderately in people with iron deficiency but not anemia who were undergoing exercise training. This isn't a systematic assessment of studies.
grade-d - High See all 3 studies
It's unclear if iron supplementation consistently improves aerobic exercise in people without anemia but deficient or low iron levels. This is not a systematic evaluation of studies.
grade-d - - See study
One study didn't find an effect in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in non-anemic but deficient participants in one study. This is not a systematic assessment of studies.
grade-d - - See study
No apparent effect in one study of people with iron deficiency but not anemia. This is not a systematic assessment of studies.
grade-d - - See study
There was a small, nonsignificant improvement in one study of people with moderately low iron levels but not anemia. This isn't a systematic assessment of studies.

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Frequently Asked Questions and Articles on Iron

Are cast iron pans unsafe?
Cast iron pans are popular, especially for searing, and are generally safe to use. But they can leach iron, which is a strong pro-oxidant. Those genetically at risk for iron overload should learn more about cast iron safety.

Things to Note

Is a Form Of

  • Taking some food and liquid with your iron supplement will reduce the chance of a stomach upset.

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Click here to see all 198 references.