Iron

What is iron used for?

Updated 9 Nov 2026

Short answer

Iron supplements are used to prevent and treat iron deficiency, the most common cause of anemia.[1] In a Cochrane review of trials in menstruating women, daily iron cut the risk of anemia by 61% (10 trials, 3,273 women) and raised hemoglobin.[2]

Other effects show up mainly in people who lack iron:

  • Tiredness: in 4 trials with 714 adults who had low iron but no anemia, iron reduced self-reported fatigue.[3] More on energy.
  • Pregnancy: a 2024 Cochrane review of 57 trials found that daily iron may reduce anemia at term (4.0% against 7.4%) and probably reduces low birthweight slightly (5.2% against 6.1%).[4]
  • Exercise: in 18 trials in women of childbearing age, iron raised VO2max, a measure of aerobic fitness, by 2.35 mL/kg/min.[5] In adults with low iron but no anemia, it did not improve measured physical capacity.[3] More on fitness.
  • Thinking in school children: in 13 studies in children aged 6 to 12, iron improved scores of intelligence, attention and memory, but not school results.[6] More on cognition.

In people with heart failure and low iron, a trial of iron by mouth found no gain in exercise capacity over 16 weeks.[7]

Sources (7)

  1. Iron: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  2. Daily iron supplementation for improving anaemia, iron status and health in menstruating women. Low MS, Speedy J, Styles CE, De-Regil LM, Pasricha SR Cochrane Database Syst Rev, 2016. PMID 27087396
  3. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. Houston BL, Hurrie D, Graham J, Perija B, Rimmer E, Rabbani R, et al. BMJ Open, 2018. PMID 29626044
  4. Daily oral iron supplementation during pregnancy. Finkelstein JL, Cuthbert A, Weeks J, Venkatramanan S, Larvie DY, De-Regil LM, et al. Cochrane Database Syst Rev, 2024. PMID 39145520
  5. Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis. Pasricha SR, Low M, Thompson J, Farrell A, De-Regil LM J Nutr, 2014. PMID 24717371
  6. Effects of iron supplementation on cognitive development in school-age children: Systematic review and meta-analysis. Gutema BT, Sorrie MB, Megersa ND, Yesera GE, Yeshitila YG, Pauwels NS, et al. PLoS One, 2023. PMID 37368919
  7. Effect of Oral Iron Repletion on Exercise Capacity in Patients With Heart Failure With Reduced Ejection Fraction and Iron Deficiency: The IRONOUT HF Randomized Clinical Trial. Lewis GD, Malhotra R, Hernandez AF, McNulty SE, Smith A, Felker GM, et al. JAMA, 2017. PMID 28510680

More about iron

What is iron?Which foods contain iron?How long does it take for iron supplements to work?What are the signs of iron deficiency?Is iron safe?Does iron help with tiredness?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.