Iron
Compare iron supplements by price per mg of elemental iron.
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How elemental iron is calculated
Iron supplements list the compound's total weight, not the bioavailable elemental iron. We compare on elemental iron — the active amount your body can absorb.
| Iron compound | % Elemental iron | Conversion factor |
|---|---|---|
| Ferrous fumarate | 33% | 0.33 |
| Ferrous sulfate (dried) | 30% | 0.30 |
| Ferrous sulfate (heptahydrate) | 20% | 0.20 |
| Ferrous gluconate | 12% | 0.12 |
| Ferrous bisglycinate | 20% | 0.20 |
| Ferric pyrophosphate | 25% | 0.25 |
| Iron polymaltose | 30% | 0.30 |
| Heme iron polypeptide | 11% | 0.11 |
Source: Australian and New Zealand Nutrient Reference Values.
Iron absorption tips
- Bioavailability: Heme iron (animal sources) absorbs ~15–35%; non-heme (plant / supplement) absorbs ~2–20%.
- Absorption boosters: Vitamin C, citrus, capsicum.
- Absorption inhibitors: Tea, coffee, calcium, high-dose zinc taken at the same time.
Types of iron supplements
1. Ferrous Salts (Iron II)
These are the most common and inexpensive forms of iron. "Ferrous" simply refers to iron in its +2 oxidation state, which is easily absorbed by the digestive tract, though they are the most likely to cause constipation or nausea.
- Ferrous Fumarate
- Ferrous Gluconate Dihydrate
- Ferrous Sulfate
2. Ferric Compounds (Iron III)
"Ferric" refers to iron in its +3 oxidation state. The body has to convert it to the +2 state before absorbing it, so it is generally absorbed slower than ferrous salts. However, they are often formulated to be gentler on the digestive system or to remain stable when mixed into foods.
- Ferric Pyrophosphate (and Iron Pyrophosphate)
- Iron Polymaltose (often used in chewable tablets or liquids; very gentle on the stomach)
3. Iron Chelates (Amino Acid Complexes)
These are forms where iron is bound (chelated) to amino acids, most commonly glycine. This binding protects the iron as it travels through the stomach, making it highly absorbable and significantly reducing gastrointestinal side effects.
- Ferric Bisglycinate
- Iron (II) Bisglycinate
- Iron (II) Glycinate
- Iron (III) Glycinate
- Iron Amino Acid Chelate
4. Heme Iron
Unlike all the others (which are non-heme, meaning they come from plant or synthetic sources), heme iron is derived from animal sources (usually bovine). It is absorbed through a completely different pathway in the gut, making it exceptionally well-absorbed and very gentle on the stomach.
- Heme Iron