Iron is the core of hemoglobin (O₂ transport in the blood) and myoglobin (O₂ store in muscle), plus a cofactor for mitochondrial enzymes of the respiratory chain. For a sport that is 100% dependent on oxygen delivery like ultramarathon, low iron is probably the single nutritional factor that hurts performance the most — and runners are the highest-risk group for deficiency in sport.
Why it matters A LOT for ultramarathon runners
- Foot-strike hemolysis: every footstrike destroys red blood cells in the sole of the foot — runners lose more iron than any other athlete.
- Sweat loss + GI bleeding: long efforts cause intestinal micro-bleeding and iron loss through sweat.
- Post-exercise hepcidin spike: intense exercise raises hepcidin (the hormone that blocks iron absorption) for ~3–6 h — a bad window to take iron or eat iron-rich foods.
- Increased turnover: training stimulates production of new red blood cells → higher iron demand.
- Low-carb/restricted diet: cutting grains/legumes lowers baseline iron intake.
- Direct link to "heavy legs" and RED-S: iron deficiency — even without anemia — already causes fatigue, heavy legs, poor recovery and a drop in performance. It is one of the first things to check.
The 3 stages of deficiency (important)
| Stage | Ferritin | Hemoglobin | Symptom / performance |
|---|---|---|---|
| 1 · Store depletion | Low (<30 ng/mL) | Normal | Already impairs endurance; subtle fatigue |
| 2 · Iron-deficient erythropoiesis | Low | Normal/borderline | Heavy legs, clear drop in performance |
| 3 · Iron-deficiency anemia | Very low | Low | Performance collapses; severe fatigue |
The classic mistake is only acting at stage 3 (anemia). Stages 1 and 2 (low ferritin, normal hemoglobin) already steal performance and are exactly what an athlete should monitor — you can't see it on a simple blood count, you need to measure ferritin.
Ferritin targets — an endurance athlete ≠ the lab "normal"
| Ferritin range | Interpretation for a runner |
|---|---|
| <15 ng/mL | Clear deficiency (even "normal" in some labs) |
| 15–30 ng/mL | Suboptimal for endurance — replenish |
| 30–50 ng/mL | Minimum acceptable zone; many sports physicians aim for >40 |
| >50 ng/mL | Good for performance (without excess) |
The lab "normal reference value" can start at 12–15 ng/mL — enough to avoid anemia, insufficient for performance. Sports medicine usually aims for ferritin >30–40 ng/mL in symptomatic athletes.
Primary product: Life Extension Iron Protein Plus
Iron Protein Plus by Life Extension uses succinylated iron protein — a well-tolerated form (less constipation/nausea than classic ferrous sulfate).
- Composition/capsule: ~28 mg elemental iron (succinylated protein)
- Bottle: 100 capsules
- Price: $10.50 USD
- Cost/dose: R$0.54
- Where to buy: Life Extension website, iHerb (international shipping)
Alternative: Iron bisglycinate (BR)
Chelated ferrous bisglycinate (several Brazilian brands: Vitgold, Lavitan, compounded) is the best value-for-money form available in Brazil — chelated, high absorption and very low gastric irritation compared to ferrous sulfate.
- Typical composition: 28–30 mg elemental iron/capsule
- Bottle: 60 capsules
- Average price: R$35.00
- Cost/dose: R$0.58
- Where to buy: pharmacies, supplement e-commerce
How to take (the part almost everyone gets wrong)
- Alternate days, single dose: modern research (Stoffel et al.) shows that taking iron on alternate days absorbs more total iron than daily split doses — because each dose raises hepcidin for ~24 h, blocking absorption of the next dose. Less is more.
- Fasted + Vitamin C: take with 200–500 mg of vitamin C (or orange/lemon juice), which greatly increases non-heme iron absorption.
- Away from calcium, coffee, tea and dairy: calcium, tannins (coffee/tea) and phytates compete and block absorption. Space ≥2 h from Calcium and coffee.
- Don't take right after hard training: hepcidin stays elevated 3–6 h after intense exercise — a bad window. Prefer the morning on an easy day, or ≥3 h after a hard session.
- Reassess in 8–12 weeks: ferritin rises slowly. Re-test before assuming it "didn't work".
For whom supplemental iron is most important
- High-volume runners with ferritin <30 ng/mL
- Women of reproductive age (menstrual losses add to training losses)
- Vegetarians/vegans and restricted low-carb diets (less heme iron)
- Anyone reporting heavy legs, persistent fatigue, poor recovery despite adequate training and sleep
- Athletes in a calorie deficit / at risk of RED-S
- Anyone using a multivitamin without iron (e.g., LE Two-Per-Day contains no iron — a deliberate brand decision)
When NOT to use / cautions
- Hemochromatosis or iron overload: absolute contraindication.
- Normal/high ferritin: supplementing brings no benefit and creates risk — more iron does not help someone who already has enough.
- No blood test: don't "take it just in case". It is the only mineral in this guide that can cause real harm from excess.
- Active inflammation: ferritin is an acute-phase protein — it rises in inflammation/infection and can mask deficiency. Interpret with CRP/context.