What Is Iron and How Does It Work?
Iron is an essential mineral that the body cannot produce on its own. Its most critical function is as the central component of haemoglobin — the protein in red blood cells that carries oxygen from the lungs to every tissue in the body. Iron is also a component of myoglobin (oxygen storage in muscle) and is involved in energy metabolism via mitochondrial enzymes.
When dietary iron intake is insufficient — or when losses exceed intake (through menstruation, intense exercise, or inadequate diet) — iron stores decline. Mild deficiency without anaemia can impair energy and physical capacity; full iron-deficiency anaemia causes significant fatigue, reduced exercise tolerance, and impaired cognitive function.
Forms of dietary iron
Haem iron (from animal foods) is absorbed more efficiently than non-haem iron (from plant foods and supplements). Vitamin C consumed alongside non-haem iron improves its absorption, while tannins (in tea and coffee) and calcium can inhibit it.
What the RCT and Meta-Analysis Evidence Shows
Iron supplementation evidence is strongest and clearest in populations with confirmed deficiency. A Cochrane review by Pasricha et al. (2013) on iron supplementation for school-age children with and without anaemia found that supplementation improved iron status and had positive effects on cognitive outcomes in iron-deficient children (Pasricha et al., 2013).
For athletes, a systematic review and meta-analysis by Burden et al. (2015) examined iron supplementation in physically active adults. The review found that iron supplementation improved iron status and was associated with improvements in maximal oxygen uptake in iron-deficient non-anaemic athletes, though effects in iron-sufficient athletes were minimal (Burden et al., 2015).
In premenopausal women — a population with high iron-loss rates due to menstruation — a meta-analysis by Haider et al. (2013) found that iron supplementation significantly reduced fatigue in women with iron deficiency without clinical anaemia (Haider et al., 2013).
Effect Sizes and Who Benefits
Iron evidence is genuinely strong — for the right population. People who benefit from supplementation are:
- People with confirmed iron deficiency (assessed by serum ferritin, full blood count)
- Premenopausal women with high menstrual losses
- Endurance athletes with elevated iron losses through sweat, haemolysis, and restricted intake
- Vegans and vegetarians relying solely on non-haem iron sources
For people with normal iron status, supplementing iron carries potential risks — excess iron is pro-oxidant and may cause gastrointestinal side effects. Routine supplementation without testing is not recommended.
EFSA-Approved Claims
EFSA has authorised several claims for iron: iron contributes to normal cognitive function; iron contributes to normal energy-yielding metabolism; iron contributes to normal formation of red blood cells and haemoglobin; iron contributes to normal oxygen transport in the body; iron contributes to the normal function of the immune system; and iron contributes to the reduction of tiredness and fatigue.
Honest Verdict
Iron is one of the nutrients with the clearest evidence base — but effectiveness is entirely dependent on the individual's iron status. Supplementing without knowing your baseline ferritin level is potentially wasteful and carries a small risk of harm. Get tested first, then supplement if needed.
Iron supplement options are available at maxfit.ee in the iron category.
FAQ
How do I know if I need an iron supplement?
The most reliable indicator is a blood test measuring serum ferritin. Symptoms like persistent fatigue, poor exercise tolerance, pale skin, and cold hands can suggest deficiency, but they are non-specific. Consult a healthcare professional for testing before starting supplementation.
Can athletes become iron deficient?
Yes. Endurance athletes are particularly vulnerable due to iron losses through sweat, foot-strike haemolysis (in runners), and chronic gastrointestinal microbleeding. Female athletes are at especially high risk. Regular monitoring is advisable.
What happens if I take iron when I do not need it?
Excess iron intake can cause constipation, nausea, and abdominal discomfort. Chronically high iron levels may contribute to oxidative stress. Iron is not a supplement to take "just in case" without a confirmed need.
References
Pasricha, S. R., Hayes, E., Kalumba, K., & Biggs, B. A. (2013). Effect of daily iron supplementation on health in children aged 4–23 months: a systematic review and meta-analysis of randomised controlled trials. The Lancet Global Health, 1(2), e77–e86. https://doi.org/10.1016/S2214-109X(13)70046-9
Burden, R. J., Morton, K., Richards, T., Whyte, G. P., & Pedlar, C. R. (2015). Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis. British Journal of Sports Medicine, 49(21), 1389–1397. https://doi.org/10.1136/bjsports-2014-093624
Haider, B. A., Olofin, I., Wang, M., Spiegelman, D., Ezzati, M., & Fawzi, W. W. (2013). Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis. BMJ, 346, f3443. https://doi.org/10.1136/bmj.f3443
