Form Comparison

Ferrous Fumarate vs Ferrous Sulfate

How ferrous fumarate and ferrous sulfate differ in elemental content, absorption, tolerance, and cost.

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Quick verdict. Same ferrous iron, same DMT1 absorption, same GI side effects per milligram of elemental iron. Fumarate packs more iron per tablet (33% vs 20%), which is why prenatal vitamins favor it; sulfate is the reference form in most trials. Compare products by elemental iron on the panel, not tablet weight, and pick whichever tablet fits your target dose.

Side by Side

Ferrous Fumarate Ferrous Sulfate
Elemental content 33% elemental iron 20% elemental iron
Absorption High High
How it is absorbed Ferrous iron absorbed by DMT1, as with sulfate. Ferrous (Fe2+) iron is absorbed by divalent metal transporter 1 (DMT1) in the duodenum. Absorption rises when stores are low and falls as hepcidin rises after a dose.
Typical dose 65-106 mg elemental iron per tablet 40-65 mg elemental iron daily or on alternate days for deficiency
Common uses iron deficiency, prenatal vitamins iron deficiency anemia, first-line oral repletion
Side effects Similar to sulfate per mg of elemental iron. Nausea, constipation, dark stools, epigastric pain; dose-dependent.
Cost Low Low
Also called iron fumarate iron sulfate
Labels in index 190 101

When to Choose Ferrous Fumarate

Choose ferrous fumarate when you want more iron per tablet. Highest elemental percentage of the common ferrous salts.

Ferrous Fumarate

Choose ferrous fumarate when you want more iron per tablet.

What to look for: Ferrous Fumarate named on the Supplement Facts panel, with the amount per serving stated.

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When to Choose Ferrous Sulfate

Choose ferrous sulfate when you want the cheapest proven repletion and tolerate it. The reference form against which others are compared. A single morning dose on alternate days improved fractional absorption versus daily dosing in Stoffel 2017.

Ferrous Sulfate

The reference standard: cheapest, best studied, and the form used in the hepcidin dosing trials. GI side effects are the price.

What to look for: 65 mg elemental iron (325 mg tablet), not enteric coated, taken once in the morning on alternate days.

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Products on Titrate

In Titrate's index of NIH label data, 190 labels named as iron products list ferrous fumarate and 101 list ferrous sulfate.

Open supplement search

Iron does not have its own search category yet. Each product above links to its full label in the NIH database.

Related

References

NIH Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals.

Hallberg L, Brune M, Rossander L. Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate. Am J Clin Nutr. 1989;49(1):140-144.

Moretti D, et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood. 2015;126(17):1981-1989.

Tolkien Z, et al. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One. 2015;10(2):e0117383.

Stoffel NU, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematol. 2017;4(11):e524-e533.

Stoffel NU, et al. Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women. Haematologica. 2020;105(5):1232-1239.

World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Geneva: WHO; 2020.