mineral · for low stamina
Iron
Iron carries oxygen to muscle. Even mildly low iron cuts what you can do.
Say that in clinical terms
Iron is critical for oxygen transport via hemoglobin and muscle oxygen storage via myoglobin. It also supports mitochondrial cytochrome function. Even subclinical iron deficiency (low ferritin, normal hemoglobin) reduces exercise capacity.
How strong is the research?
3 papers read, 3 supporting.
Tested as: Ferrous Sulfate
Who was studied: Women who were low in iron but not anaemic, likely active or athletic.
A proper search found trials of this compound, but not in the form named here — Ferrous Sulfate. Evidence for one form is not evidence for another.
How much to take
daily on empty stomach
18–36 mg
Test ferritin before supplementing. Athletes and menstruating women are at higher risk of depletion. Target ferritin >30 ng/mL.
Before you take it
- NIH ODS Tolerable Upper Intake Level (UL) for iron is 45 mg/day for adults (all sources combined: food and supplements).
- Levothyroxine interaction: concurrent ingestion significantly reduces levothyroxine efficacy; separate iron and levothyroxine by at least 4 hours.
- Tetracycline and fluoroquinolone antibiotic interaction is asymmetric: take the antibiotic at least 2 hours BEFORE iron, or at least 4–6 hours AFTER iron — not a simple equal-interval separation.
- Levodopa interaction: iron may reduce levodopa absorption via chelation; separate administration times (specific interval not fixed in NIH ODS guidance).
- Proton pump inhibitors (e.g., omeprazole, lansoprazole) reduce gastric acid and may impair non-heme iron absorption, potentially reducing efficacy of oral iron supplementation.
- Hereditary hemochromatosis (HFE gene mutation): iron supplementation is contraindicated; risk of iron overload, organ damage.
- GI side effects (constipation, nausea, abdominal discomfort) are common with oral iron; iron bisglycinate is better tolerated than ferrous sulfate in comparative trials but is not side-effect-free.
- Accidental ingestion by children can be fatal; child-resistant storage is essential.
- Iron supplementation without confirmed deficiency (serum ferritin or CBC) has no established benefit for symptom relief and risks cumulative toxicity approaching or exceeding the 45 mg/day UL when combined with dietary iron.
- Iron supplementation without confirmed deficiency (serum ferritin or CBC) carries no established benefit for exercise performance or stamina; benefit in trials is restricted to iron-deficient or iron-depleted populations.
When to take it
Best taken: empty stomach
What we make of it
The biology is sound, but three limits undercut it.
The detail
Iron deficiency genuinely reduces exercise capacity by cutting oxygen delivery, so the reasoning holds. The trial itself carries serious limits on who was studied and how far the result stretches.