Compound or practice · Supplement
Iron
Only supplement it against a ferritin number — transformative in deficiency, pro-oxidant and constipating in excess.
- Overall grade
- Grade A
- Last revised
- 3
- graded outcomes
- 0
- references listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
1 at grade A · 2 at grade B — 3 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Iron-deficiency anemiaEvidence grade A
Definitional
Largehigh
- Fatigue with low ferritin (non-anemic)Evidence grade B
Benefit when ferritin is low
Moderatemixed
- Restless legs syndromeEvidence grade B
When iron-deficient
Moderatemixed
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Studies disagree: Fatigue with low ferritin (non-anemic) (mixed agreement); Restless legs syndrome (mixed agreement).
- Watch with Calcium: Calcium blunts iron uptake — split across meals.
- Watch with Zinc: Competes for absorption — separate.
- Watch with Caffeine: Coffee polyphenols cut non-heme iron ~40% — separate 2 hours.
Interactions
Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.
CalciumMind the timing
Calcium blunts iron uptake — split across meals.
ZincMind the timing
Competes for absorption — separate.
LevothyroxineMind the timing
Binds thyroid hormone — separate by 4 hours.
CaffeineMind the timing
Coffee polyphenols cut non-heme iron ~40% — separate 2 hours.
Vitamin CWorks together
Reduces iron to its absorbable form — take together.
The evidence in words
What it is
Iron is the oxygen-carrying metal at the center of hemoglobin. Deficiency (low ferritin, then anemia) is the world's most common nutrient deficiency, especially in menstruating women, endurance athletes, and plant-based eaters. The body has no route to excrete excess, so iron status must be earned, not guessed.
How it works
Heme iron ferries oxygen in blood and muscle and shuttles electrons in mitochondria. Non-heme (plant) iron absorbs poorly and is enhanced by vitamin C and blunted by calcium, tea polyphenols, and coffee. Deficiency starves oxygen delivery and cellular energy long before anemia appears.
What the evidence shows
Grade A for iron-deficiency anemia and for symptomatic low ferritin (fatigue, exercise capacity, restless legs), where repletion is genuinely transformative. In iron-replete people, supplementation does nothing good and plausibly some harm, because free iron is pro-oxidant. Diagnosis by ferritin (± transferrin saturation) is the whole game.
How to use it
Treat against a lab value under medical guidance. Emerging evidence favors alternate-day dosing (e.g., 60–120 mg elemental every other day) for better absorption and fewer side effects. Take with vitamin C, away from calcium, coffee, and tea.
Safety & interactions
Constipation and GI upset are common; overdose is dangerous, and iron is a leading cause of pediatric poisoning — store away from children. Never supplement chronically without confirmed need; hereditary hemochromatosis makes iron actively harmful. Vitamin C — Reduces iron to its absorbable form — take together. Calcium — Calcium blunts iron uptake — split across meals. Zinc — Competes for absorption — separate. levothyroxine — Binds thyroid hormone — separate by 4 hours. Caffeine — Coffee polyphenols cut non-heme iron ~40% — separate 2 hours.
Bottom line
Get ferritin tested before you touch it. If low, iron with vitamin C (ideally alternate-day) fixes real fatigue. If normal, skip it — more iron is not more energy.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Repletion
- 60–120 mg elemental, alternate-day, with vitamin C, under care.
Goes with
- Vitamin CReduces iron to its absorbable form — take together.Evidence grade A
Related reading
Entries that share this one's tags or conditions.
- Iron for Fatigue with low ferritin (non-anemic)Evidence grade B — Benefit when ferritin is lowEvidence grade B
- Iron for Iron-deficiency anemiaEvidence grade A — DefinitionalEvidence grade A
- Iron for Restless legs syndromeEvidence grade B — When iron-deficientEvidence grade B
- Iron: dosage and how to take it60–120 mg elemental, alternate-day, with vitamin C, under care.Evidence grade A
Sources
This entry lists no references of its own.
Last revised . A grade is this entry's reading of the evidence, not medical advice.