Iron

What is Iron?

Iron is an essential dietary mineral present in a wide variety of foods, but the iron found in plants (notably grains and legumes) is less bioavailable than the iron found in meat (in the form of heme). Its main role in the body is as a critical part of hemoglobin, red blood cells' oxygen-carrier, and a deficiency in iron leads to poor oxygen transport (anemia) In addition, iron is a cofactor for many enzymes. It 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 make it toxic to a wide variety of cells. Iron deficiency is the only reason to consider iron supplementation, though getting more iron through foods should be preferred when possible. For people who already have enough iron, taking an iron supplement has no proven benefit; on the contrary, it can lead to iron overdose.

What are Iron's benefits?

A lack of iron will tend to produce fatigue, depression, impaired cognitive function, restless leg syndrome, and other adverse effects. The correction of iron deficiency will tend to improve symptoms, and even among people who aren't anemic, there may be a need for more than the bare minimize to produce optimal amounts of hemoglobin and reap the benefits of greater oxygen deliver, though more research is needed, and the effect is probably limited to people with low iron levels by conventional standards. 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 Iron's downsides?

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

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

• 8 mg for men and non-menstruating women

• 15 mg for menstruating women under 19

• 18 mg for menstruating women over 18

• 27 mg for pregnant women

• 9 mg for lactating women under 19

• 10 mg for lactating women over 18

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

For more details, see the Recommended Intake section below.

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects iron has on your body, and how strong these effects are.

Grade	Level of Evidence [show legend]
	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
	Fatigue (non-anemic)	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.
	Alertness	Minor	- See study	One study found a small increase in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
	Anxiety	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.
	Calmness	Minor	- See study	One study found a small increase in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
	Depression	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.
	Muscular Endurance	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.
	VO₂ Max	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.
	Aerobic Exercise	-	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.
	Attention	-	- See study	One study didn't find an effect in iron-deficient but non-anemic participants. This isn't a systematic assessment of studies.
	Heart Rate	-	- See study	No apparent effect in one study.
	Memory	-	- See study	No apparent effect in non-anemic but deficient participants in one study. This is not a systematic assessment of studies.
	Respiratory Exchange Ratio	-	- See study	No apparent effect in one study of people with iron deficiency but not anemia. This is not a systematic assessment of studies.
	Subjective Well-Being	-	- 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.

• Can restless legs be ‘ironed out’?

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