Iron (Ferrous Sulfate)
Also known as: ferrous sulfate, ferrous sulphate, iron(II) sulfate heptahydrate, FeSO4
The reference iron salt used in most clinical research and public-health programs, inexpensive and reliably absorbed. The heptahydrate is about 20% elemental iron; the dried monohydrate is closer to 30%. Its main drawback is gastrointestinal upset at the doses used for iron deficiency, which is why gentler chelates have taken market share in consumer products. Alternate-day dosing has been shown to improve absorption and tolerance.
Research summary
Supplies soluble ferrous iron absorbed through DMT1 in the duodenum for hemoglobin synthesis and oxygen transport.
Dosage
Daily amounts, elemental (20% of the compound is the element).
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 15 mg | 18–45 mg | 45 mg | 45 mg |
NIH ODS — UL of 45 mg/day for adults; higher amounts are used only under medical supervision
Doses are elemental iron. Absorbed best on an empty stomach but often taken with food to limit nausea, constipation, and dark stools. Stoffel 2017 showed higher fractional absorption when 60 mg doses were given on alternate days rather than daily. Deficiency protocols use 60–200 mg/day under supervision; the app caps at the 45 mg UL. Heptahydrate (MW 278) ≈ 20% Fe; dried monohydrate ≈ 30% — verify grade. Keep out of reach of children.
Source material: synthetic (steel pickling by-product refined to food grade, or direct synthesis)
As supplied: Heptahydrate ≈ 20% Fe; dried/monohydrate ≈ 30% Fe
Forms of Iron
| Form | Typical dose | Element % | Formats | Price |
|---|---|---|---|---|
| Iron (Ferrous Sulfate) | 18–45 mg | 20% | Capsule, Tablet, Liquid | low |
| Iron Bisglycinate | 18–30 mg | 20% | Capsule, Powder, Tablet, Gummy, Liquid | mid |
| Iron (Ferrous Fumarate) | 18–45 mg | 33% | Capsule, Tablet, Powder | low |
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
Strong metallic taste and a tendency to oxidize and discolor, so it is rarely used in gummies or flavored powders. Coated tablets are the standard consumer format. Hygroscopic; heptahydrate cakes in humid storage.
Formulation notes
Vitamin C taken in the same serving raises non-heme iron absorption and is the classic pairing. Separate from calcium, zinc of 25 mg or more, tea, coffee, and antacids by about two hours. Iron lowers absorption of levothyroxine, tetracyclines, quinolones, and levodopa.
- Has an upper limit
Sources
- Iron — Health Professional Fact SheetNIH ODS
- 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 (Stoffel 2017)PubMed
- A comparison of the bioavailability of ferrous fumarate and ferrous sulfate in non-anemic Mexican women and children consuming a sweetened maize and milk drink (Harrington 2011)PubMed
Related ingredients
Iron Bisglycinate
MineralFerrous iron chelated with two glycine molecules, the form most prenatal and gentle-iron products now use.
Typical: 18–30 mg
Potassium Iodide
MineralThe standard iodine source in multivitamins, prenatals, and thyroid-support formulas, about 76.5% iodine by weight and absorbed almost completely.
Typical: 150–300 mcg
Iron (Ferrous Fumarate)
MineralA ferrous salt of fumaric acid that carries about 33% elemental iron, the highest of the common iron forms, which keeps tablets small.
Typical: 18–45 mg
Vitamin B6 (Pyridoxine HCl)
VitaminPyridoxine hydrochloride is the standard, inexpensive, and highly stable form of vitamin B6 used in nearly all multivitamins and B-complex products.
Typical: 1.7–50 mg
Kelp (Iodine)
MineralBrown seaweed, usually Laminaria or Ascophyllum species, used as a whole-food iodine source in thyroid and multimineral formulas.
Typical: 150–300 mcg