Iron Supplements: Ferrous Fumarate vs Bisglycinate vs Polysaccharide-Iron (FeraMAX)
Short answer: what matters most on an iron label is the amount of elemental iron, not the weight of the iron compound. Ferrous fumarate is about 33% elemental iron by weight, so a 300 mg tablet gives roughly 99 mg of iron; ferrous sulfate is about 20%; ferrous gluconate about 12%. Iron bisglycinate (a chelate bound to the amino acid glycine) and polysaccharide-type complexes such as the polydextrose-iron complex in FeraMAX are newer forms that makers describe as easier on the stomach. How well each form is absorbed, and how your stomach copes with it, differs between forms and between people. Before you pick any of them, confirm with a blood test that you actually need iron.
The main forms compared
| Form | What it is | Elemental iron | Example in stock |
|---|---|---|---|
| Ferrous fumarate | A traditional iron salt | About 33% of the compound's weight (300 mg ≈ 99 mg iron) | Wampole Ferrous Fumarate 300 mg |
| Ferrous gluconate | A traditional iron salt with less iron per milligram | About 12% of the compound's weight | Check the medicinal ingredient on the label |
| Iron bisglycinate | Iron chelated (bound) to glycine | Listed per capsule on the label | Ferrochel Iron Chelate, NFH Iron SAP |
| Polysaccharide-type iron complex | Iron bound to a carbohydrate; FeraMAX Pd uses a polydextrose-iron complex | Listed per capsule on the label | FeraMAX Pd Therapeutic 150 (150 mg elemental iron per capsule) |
Ferrous sulfate is the other classic salt: the Wampole ferrous sulfate 300 mg tablet lists 60 mg of elemental iron. For a lower-strength tablet, Novo-Ferrogluc lists 35 mg of elemental iron per tablet.
What "elemental iron" means
An iron compound is iron plus something it is bound to. Only the iron part counts toward your intake, so two products with the same "300 mg" on the front can deliver very different amounts of iron. Compare products by the elemental iron per tablet or capsule, which is shown on the label, and check it against the dose your health professional recommends.
Absorption and stomach tolerance
Constipation, nausea, stomach upset and dark stools are common with oral iron, and they are a main reason people stop. Bisglycinate and polysaccharide-type complexes are marketed as gentler; the FeraMAX page describes its form as chosen to be easier on the stomach than many traditional iron salts. Individual experience varies, so if one form doesn't agree with you, ask your pharmacist about switching rather than stopping on your own. Taking iron with food can reduce stomach upset, as the FeraMAX directions note.
Tips for taking iron
- Space it from calcium, tea and coffee. Health Canada advises waiting 1 to 2 hours after a meal before drinking tea or coffee or taking calcium supplements, to improve iron absorption. The NIH Office of Dietary Supplements (ODS) notes that taking calcium and iron supplements at different times of day may avoid the interaction.
- Add vitamin C. Vitamin C helps your body absorb the iron in plant foods and supplements. The Wampole label suggests taking its iron with a vitamin C source such as orange juice.
- Keep it apart from some medicines. Iron can interfere with thyroid medication, some antibiotics and antacids; product pages recommend spacing them about 2 hours apart. Ask your pharmacist about your own medicines.
- Don't double up. Count the iron in multivitamins and prenatal vitamins too.
How much iron do you need? (Canadian DRIs)
Health Canada uses the Dietary Reference Intakes. The Recommended Dietary Allowance (RDA) is what meets the needs of almost all healthy people in a group; the tolerable upper intake level (UL) is the most from all sources (food plus supplements) that is unlikely to cause harm in healthy people.
| Group | RDA per day | UL per day |
|---|---|---|
| Children 9–13 | 8 mg | 40 mg |
| Teen males 14–18 | 11 mg | 45 mg |
| Teen females 14–18 | 15 mg | 45 mg |
| Men 19 and older | 8 mg | 45 mg |
| Women 19–50 | 18 mg | 45 mg |
| Women 51 and older | 8 mg | 45 mg |
| Pregnancy (19 and older) | 27 mg | 45 mg |
| Breastfeeding (19 and older) | 9 mg | 45 mg |
Therapeutic iron products, such as FeraMAX Pd Therapeutic 150, contain more than the UL per dose. The ODS notes that doctors sometimes prescribe doses above the UL for a while to treat iron deficiency. These higher amounts are for a diagnosed deficiency, under the care of a health professional, not for general use.
Safety box
- Keep iron out of children's reach. Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. If a child swallows iron, call your poison centre or 911 right away.
- Test first, don't guess. Tiredness has many causes, and extra iron you don't need can build up in the body. Ask for a blood test (such as ferritin and a complete blood count) before taking iron, and don't take iron if you have an iron-overload condition.
When to see a doctor or pharmacist
- Before starting iron, to confirm low iron and find the cause, especially if you have heavy periods, are pregnant, or follow a vegetarian or vegan diet.
- If you have a peptic ulcer, inflammatory bowel disease, or take thyroid medication or antibiotics.
- For severe stomach pain, vomiting, vomiting blood, or ongoing constipation or diarrhea while taking iron.
- To decide how long to take it and when to re-test.
Read more in Iron Deficiency Symptoms: When to Test, Not Guess, and browse the full range in our Iron collection.
Related guides: Beef Liver Supplements vs Iron Supplements · How to Read a Natural Health Product Label in Canada · How to Check an NPN or DIN on Health Canada's Database
Sources
- Health Canada. Iron (vitamin C; wait 1 to 2 hours after a meal for tea, coffee or calcium supplements).
- Health Canada. Dietary Reference Intakes tables: Reference values for elements (iron RDA and UL).
- Health Canada. Guidelines for Canadian Drinking Water Quality: Iron (summary of iron RDAs and ULs).
- NIH Office of Dietary Supplements (U.S.; background). Iron: Fact Sheet for Health Professionals (elemental iron by form; calcium; doses above the UL; poisoning risk in children under 6).
- NIH Office of Dietary Supplements (U.S.; background). Iron: Fact Sheet for Consumers.
- ISMP Canada. Take care with iron supplements (safe storage; poison centre).
- Product details: the Canadian product pages linked above (FeraMAX, Wampole, Novo-Ferrogluc, Ferrochel, NFH).
This guide is general information, not medical advice. Ask your pharmacist or doctor about your own situation.