Iron

Does it work?

• -Only if your ferritin is genuinely low. Iron fixes the deficiency, and in iron-deficient athletes that translates into real endurance and recovery gains. But if your iron stores are already normal, supplementing does nothing for performance — and too much iron is harmful. Get a blood test before you touch it.

How much · when

• -Test first. Get a blood panel with ferritin (plus hemoglobin and CRP). Supplement only if ferritin is low — commonly flagged below ~20-30 ng/mL in athletes. Don't guess.
• -If deficient, ~100 mg elemental iron/day (e.g. ferrous sulfate) is the studied dose. Give it 6-8 weeks minimum to move ferritin, then retest.
• -Take it on an empty stomach with vitamin C (or orange juice) to boost absorption. Avoid taking it with coffee, tea, calcium, or dairy, which blunt it.
• -Alternate-day dosing absorbs as well as daily and is gentler on the gut — worth trying if daily iron upsets your stomach.
• -Once ferritin is restored, stop. Maintenance comes from food (red meat, organ meats, legumes); ongoing pills aren't needed unless you keep losing iron.

The catch

• -If your ferritin is already normal, iron does nothing for VO2max, endurance, or recovery — the gains only show up in people who were deficient.
• -Iron has no off-switch. The body can't excrete excess, so blind supplementation can push stores too high over time. More is not better.
• -Endurance women, vegetarians, and heavy-training athletes are the ones most likely to actually be low — most everyone else isn't.

Better option

• -Get a ferritin test; if it's normal, skip the pills and cover iron through food instead.

Safety

• -Don't supplement without a blood test. Excess iron accumulates and is toxic to the liver and heart; it can also mask or worsen hereditary hemochromatosis.
• -GI side effects (constipation, nausea, dark stools, cramping) are common. Lower the dose, take with food, or switch to alternate-day dosing if it bothers you.
• -Iron is a leading cause of fatal poisoning in young children — keep it locked away. And don't combine multiple iron-containing products.

Key research

• American College of Sports Medicine Joint Position Statement. Nutrition and Athletic PerformanceMed Sci Sports Exerc · 2016 · Position stand
• IOC consensus statement: dietary supplements and the high-performance athleteBr J Sports Med · 2018 · Position stand
• Effects of Oral Iron Supplementation on Blood Iron Status in Athletes: A Systematic Review, Meta-Analysis and Meta-Regression of Randomized Controlled TrialsSports Medicine · 2024 · Meta-analysis
• Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysisJ Nutr · 2014 · Meta-analysis
• Iron deficiency, supplementation, and sports performance in female athletes: A systematic reviewJ Sport Health Sci · 2025 · Systematic review

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