Iron
Also called: ferrous sulfate, ferrous fumarate, ferrous gluconate, iron bisglycinate.
A supplement not to take blindly: useful in documented deficiency, debatable otherwise, and highly dependent on what goes with it at the meal.
What it is
Iron carries oxygen in the blood through hemoglobin and in muscle through myoglobin. The body has no active excretion pathway to get rid of it, which makes excess as much of a problem as deficiency. People buy it mostly for fatigue.
What the label does not say
- The percentage of elemental iron ranges from 12 to 33% depending on the salt. Two products showing the same number of milligrams do not provide the same iron dose if one declares the salt and the other elemental iron.
- Vitamin C taken at the same meal increases non-heme iron absorption; tea, coffee and phytates reduce it. The Linus Pauling Institute reports that 5 to 10 mg of phytic acid is enough to cut absorption in half.
- A stable-isotope trial in anemic women reports fractional absorption 40 to 50% higher with dosing every other day than with daily dosing, because the previous day's dose raises hepcidin. The label still says every day.
- The Linus Pauling Institute writes that people not at risk, including adult men and postmenopausal women, should not take iron without medical assessment, in particular because of undetected hereditary hemochromatosis.
The forms on the shelf
- Heme iron, found in lean meat and seafood: absorption of 14 to 18% in a mixed diet containing meat, seafood and vitamin C.
- Non-heme iron, found in nuts, legumes, vegetables and fortified grain products: absorption of 5 to 12% in a vegetarian diet.
- Ferrous sulfate: 20% elemental iron (33% for the monohydrate form according to the Linus Pauling Institute). Ferrous fumarate: 33%. Ferrous gluconate: 12%.
Published reference values
- Recommended intake: 8 mg per day for adult men, 18 mg for women aged 19 to 50, 8 mg from 51 onward, 27 mg during pregnancy.
- Upper limit: 45 mg per day for adults.
- At 45 mg per day and above, the NIH reports digestive effects: nausea, constipation, abdominal pain, vomiting, diarrhea.
- The NIH points out that accidental overdose of iron-containing products is a major cause of fatal poisoning in children under 6.
When
Absorption is better on an empty stomach, tolerance is better with a little food. A source of vitamin C at the same meal helps; tea and coffee at the same meal hurt.
Keep apart from
- Levothyroxine: the monographs advise against taking it within 4 hours of an iron supplement.
- Levodopa: iron reduces its absorption, possibly through chelation.
- Calcium: reduces the bioavailability of both heme and non-heme iron.
- Proton pump inhibitors: reduce iron absorption, which depends on stomach acidity.
To mention to a professional
- Hereditary hemochromatosis or a family history of it, unexplained anemia, inflammatory disease, pregnancy: blood work including ferritin before supplementing is something to discuss with a health care professional.
From the plate first
Lean meats and seafood for heme iron. Legumes, nuts, vegetables and fortified grain products for non-heme iron, which is less well absorbed.
Sources
- NIH Office of Dietary Supplements, Iron (Health Professional)
- Linus Pauling Institute, Micronutrient Information Center, Iron
- Stoffel et al., Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women, Haematologica
- Health Canada, Dietary Reference Intakes, reference values for elements
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.