Form Comparison

Ferrous Gluconate vs Ferrous Sulfate

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

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Quick verdict. Gluconate is not gentler per milligram of iron; it only seems so because each tablet holds less (12% elemental vs 20% for sulfate). Absorption and side effects per milligram of elemental iron are the same. Choose sulfate for the cheapest proven repletion and gluconate when you want smaller doses per tablet to ease into iron.

Side by Side

Ferrous Gluconate Ferrous Sulfate
Elemental content 12% 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 27-38 mg elemental iron per tablet 40-65 mg elemental iron daily or on alternate days for deficiency
Common uses iron deficiency, lower per-tablet dose iron deficiency anemia, first-line oral repletion
Side effects Similar to sulfate per mg of elemental iron; fewer side effects per tablet only because each tablet holds less iron. Nausea, constipation, dark stools, epigastric pain; dose-dependent.
Cost Low Low
Also called iron gluconate iron sulfate
Labels in index 67 101

When to Choose Ferrous Gluconate

Choose ferrous gluconate when you want smaller per-tablet iron doses. Lowest elemental percentage of the common ferrous salts.

Ferrous Gluconate

Choose ferrous gluconate when you want smaller per-tablet iron doses.

What to look for: Ferrous Gluconate 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, 67 labels named as iron products list ferrous gluconate and 101 list ferrous sulfate.

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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.