Iron for Anemia & Low Ferritin: How Much, How Long, How to Absorb It
Treating low iron is a months-long project, not a quick fix. Use a well-tolerated iron (bisglycinate), commonly ~60-100mg elemental, increasingly given every other day (absorbs better, gentler — Stoffel 2017, PMID: 29032957), with vitamin C.
Hemoglobin recovers in weeks; ferritin (your iron tank) takes 3-6 months. Keep going past feeling better, and retest ferritin before stopping.
And find the cause — unexplained iron deficiency in men or postmenopausal women can signal GI bleeding and needs a doctor. Solgar Gentle Iron is our value pick.
The dose — and why alternate-day is the modern approach
Standard treatment historically meant 150-200mg of elemental iron a day in divided doses — effective, but rough on the gut, and partly self-defeating. We now understand that a large iron dose spikes hepcidin, the hormone that shuts down iron absorption for roughly a day, so dosing more often doesn't proportionally help. Research showed a single dose every other day raised the absorbed fraction and cut side effects (Stoffel 2017, PMID: 29032957; Kamath 2024, PMID: 37979057). The AGA's clinical update on iron deficiency reflects this shift toward lower-frequency dosing (DeLoughery 2024, PMID: 38864796). Practically: many people do well on ~60-100mg elemental iron every other day, with vitamin C — but let your doctor set the target based on how depleted you are.
How long: the ferritin patience problem
This is where most people undershoot. There are two finish lines, and the obvious one comes first. Your hemoglobin (the anemia itself) often rebounds within a few weeks — you feel better, energy returns, and it's tempting to stop. But your ferritin, the storage tank that has to be refilled to prevent relapse, lags far behind and usually needs 3-6 months (sometimes more) of consistent iron. Stop at "I feel fine" and you typically slide right back into deficiency. The rule: keep taking iron as directed well past symptom relief, and recheck ferritin — not just hemoglobin — before you quit.
Don't skip the "why"
Iron deficiency is a symptom with a cause, and the cause sometimes matters more than the iron. In menstruating women and pregnancy, the reason is usually obvious (blood loss, higher demand). But low iron in a man or a postmenopausal woman is a genuine red flag — it commonly points to gastrointestinal bleeding, from something benign like an ulcer to, occasionally, colon cancer. Supplementing iron without finding the source can mask a problem that needs treatment. If your deficiency has no obvious explanation, the supplement is secondary to getting it investigated.
Iron for treating deficiency, ranked
| Product | Form | Elemental Iron | Servings | Price | Cost/Day | Certification (as labelled) | Buy |
|---|---|---|---|---|---|---|---|
| NOW Foods Iron 36 mg Double Strength (Ferrochel) Budget Pick | Ferrous bisglycinate | 36mg | 90 | $9.55 | $0.10 | None | Buy |
| Solgar Gentle Iron (Iron Bisglycinate) 25 mg Best Value | Ferrous bisglycinate | 25mg | 90 | $12.95 | $0.15 | None | Buy |
| Thorne Iron Bisglycinate 25 mg Quality Pick | Ferrous bisglycinate | 25mg | 60 | $16.00 | $0.27 | NSF Certified for Sport | Buy |
| MegaFood Blood Builder | Whole-food + cofactors | 26mg | 90 | $28.99 | $0.32 | NSF Certified | Buy |
Bisglycinate matters more here than usual: you'll be on iron for months, so tolerability determines whether you actually finish the job. Pair with vitamin C; keep away from calcium, coffee, and tea.
The evidence · Iron
What the published reviews of Iron concluded
- Daily oral iron supplementation during pregnancy. · The Cochrane database of systematic reviews, 2015
“Supplementation reduces the risk of maternal anaemia and iron deficiency in pregnancy but the positive effect on other maternal and infant outcomes is less clear.”
- Daily iron supplementation for improving anaemia, iron status and health in menstruating women. · The Cochrane database of systematic reviews, 2016
“Daily iron supplementation effectively reduces the prevalence of anaemia and iron deficiency, raises haemoglobin and iron stores, improves exercise performance and reduces symptomatic fatigue. These benefits come at the expense of increased gastrointestinal symptomatic side effects.”
- Efficacy of daily versus alternate day oral iron supplementation for management of anaemia among general population: a systematic review and meta-analysis. · BMC pharmacology & toxicology, 2025
“Both daily and alternate-day oral iron supplementation are comparably effective for treating IDA, with alternate-day dosing showing better tolerability. Due to low certainty in evidence, treatment decisions should be individualized pending further high-quality research.”
- Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. · BMJ open, 2018
“In IDNA adults, iron supplementation is associated with reduced subjective measures of fatigue but not with objective improvements in physical capacity.”
Method: PubMed searched in humans for systematic reviews and meta-analyses with Iron in the title; these 4 of the 38 that qualified are shown with the authors’ own conclusion quoted rather than summarised. What it cannot tell you: whether Iron will work for you — each of these reports an average across trials published 2015–2025, and null findings are shown here as readily as positive ones.
Frequently asked questions
How much iron for low ferritin/anemia?
Commonly ~60-100mg elemental, increasingly given every other day (absorbs better, gentler). The exact dose depends on how low you are — let your doctor and follow-up bloodwork guide it.
How long to raise ferritin?
Hemoglobin improves in weeks, but refilling ferritin takes ~3-6 months. Keep going past feeling better and recheck ferritin (not just hemoglobin) before stopping.
Best iron for anemia?
Any well-absorbed salt treats it; bisglycinate is far better tolerated than ferrous sulfate, so you're more likely to stay on it long enough. Pair with vitamin C, away from calcium/coffee/tea.
When is low iron serious?
Unexplained deficiency in a man or postmenopausal woman is a red flag for GI bleeding (ulcer, sometimes colon cancer) and needs investigation — don't just supplement and move on.
Related guides
- Best Iron Supplement
- Iron for Women
- Ferrous Sulfate vs Bisglycinate
- B12 & Fatigue — another deficiency to rule out
- Vitamin C — take alongside iron for absorption
Sources
- Stoffel NU, et al. "Iron absorption from oral iron supplements given on consecutive versus alternate days." Lancet Haematol. 2017;4(11):e524-e533. PMID: 29032957
- DeLoughery TG, et al. "AGA Clinical Practice Update on Management of Iron Deficiency Anemia: Expert Review." Clin Gastroenterol Hepatol. 2024. PMID: 38864796
- Kamath S, et al. "Daily versus alternate day oral iron therapy in iron deficiency anemia: a systematic review." Naunyn Schmiedebergs Arch Pharmacol. 2024. PMID: 37979057