Ferrous sulfate
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Every diet
It is chemically synthesized.
No carbohydrate.
Safe in small amounts; may bother some people or raise blood sugar.
Rules by country
Ferrous sulfate carries no E-number: it is a nutrient source, not an additive. In the United States it is permitted for fortification, and the iron in enriched flour is set by 21 CFR 137.165, which requires 20 mg of iron per pound. In the EU it is sold as a fortificant under the rules on added nutrients.
What is it?
Ferrous sulfate is a pale green crystalline salt, and roughly a fifth to a third of its weight is elemental iron depending on how much water it carries. In enriched flour the legal amount is 20 mg of iron per pound of flour, which works out to about 4 mg per 100 g. The taste is metallic and it can darken stools, which is harmless but alarming the first time you see it.
Where it comes from: Ferrous sulfate is a chemical salt of iron and sulfuric acid, made from iron ore or iron filings and acid. It is the cheap, pale-green iron fortificant that goes into enriched flour and cereals, and it is also the iron in most iron tablets.
Why it’s in food
- Fortifies flour and bread
- Adds iron to breakfast cereals
- Supplies iron in infant formula
- Feeds iron supplement tablets
Often found in
Also listed as: Ferrous sulfate, Ferrous sulphate, Iron(II) sulfate, Iron sulfate, Ferrous sulfate (iron)
Health & gut impact
EFSA puts the reference intake at 11 mg a day for adult men and postmenopausal women, and higher for women of childbearing age. A slice of fortified bread lands in the low single-digit milligrams, so a normal diet of bread and cereal can cover a good part of it. EFSA's upper level of 40 mg a day applies to iron from fortified foods and supplements, not to iron already in food.
EFSA, dietary reference values for iron
The side effects come from the dose, not the food. NHS guidance on ferrous sulfate lists constipation, nausea and stomach pain as the common complaints, and notes that the stools can go black.
NHS, iron supplements
Vitamin C taken with a plant meal raises how much iron you absorb, while tea, coffee and milk cut it. That is why a glass of orange juice alongside fortified cereal does more for iron than the cereal on its own.
EFSA, dietary reference values for iron
What can I use instead?
Ratio: The same dose of elemental iron in a gentler salt
Best for: Tablets that upset the stomach
Ratio: About 6 mg of iron per 100 g, in a single serving
Best for: Getting iron from food
Related
More vitamins & minerals:
Common questions
Does iron in bread cause constipation?
Only if the dose is high. Bread and cereal carry a small amount of iron per serving, and constipation is a complaint about iron tablets, where a single dose is far bigger. NHS advice for tablets is to start low and build up gradually.
Is iron from plants as good as iron from meat?
Not quite. Iron from meat is haem iron and is absorbed more easily, while iron from plants and fortified foods is non-haem iron, which needs vitamin C to be absorbed well. Dietary reference values count the two separately for that reason.
Why do my stools turn black?
Untreated iron turns the stool dark or black, and it is not blood. NHS advice is to expect the change and to report it only if it comes with other symptoms.
Is Ferrous sulfate safe?
Use in moderation (72/100). Ferrous sulfate carries no E-number: it is a nutrient source, not an additive. In the United States it is permitted for fortification, and the iron in enriched flour is set by 21 CFR 137.165, which requires 20 mg of iron per pound. In the EU it is sold as a fortificant under the rules on added nutrients.
Is Ferrous sulfate vegan?
Yes. It is chemically synthesized.
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Scientific sources & regulatory citations
- 21 CFR 137.165 (US FDA)
- EFSA, dietary reference values for iron
- NHS, iron supplements
CAS 7722-99-7