Form Comparison

Ferrous Sulfate vs Iron Bisglycinate

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

This page contains affiliate links. Titrate earns a small commission when you purchase through them, at no cost to you. This does not affect our recommendations.

Quick verdict. Ferrous sulfate is the reference repletion form and the cheapest per milligram of iron, and alternate-day morning dosing improves both absorption and tolerance. Bisglycinate is a chelate that phytates affect less, and trials report fewer GI complaints, partly because they used lower doses. Start with sulfate; switch to bisglycinate if constipation or nausea makes you skip doses.

Side by Side

Ferrous Sulfate Iron Bisglycinate
Elemental content 20% elemental iron 20% elemental iron
Absorption High High
How it is absorbed 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. Iron chelated to two glycine molecules. The chelate is less affected by dietary phytates than iron salts, and absorption remains regulated by iron status.
Typical dose 40-65 mg elemental iron daily or on alternate days for deficiency 25-50 mg elemental iron daily
Common uses iron deficiency anemia, first-line oral repletion iron deficiency with GI intolerance to salts, pregnancy
Side effects Nausea, constipation, dark stools, epigastric pain; dose-dependent. Typically fewer GI complaints than ferrous sulfate in trials, partly due to lower doses.
Cost Low Moderate
Also called iron sulfate ferrous bisglycinate chelate, Ferrochel, gentle iron
Labels in index 101 283

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.

Find on iHerb Affiliate link

When to Choose Iron Bisglycinate

Choose iron bisglycinate when ferrous salts cause GI side effects. Often the switch when sulfate causes constipation or nausea.

Iron Bisglycinate

Easier on the stomach for many people. Fewer head-to-head data than sulfate.

What to look for: Elemental iron stated per capsule, often 25-36 mg. Ferrochel is the most studied raw material.

Find on iHerb Affiliate link

Products on Titrate

In Titrate's index of NIH label data, 101 labels named as iron products list ferrous sulfate and 283 list iron bisglycinate.

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.