Taking Iron? Why Dose and Timing Matter More Than You Think
Once iron supplementation is indicated, how it’s taken can significantly influence whether it works — or causes unwanted side effects.
More iron isn’t better
A common assumption is that higher or more frequent dosing leads to faster correction. In reality, frequent dosing can:
Reduce iron absorption
Increase gut irritation
Worsen constipation, bloating or reflux
This happens because iron absorption is actively regulated, not passive.
Single doses beat split doses
Research shows that:
Oral iron raises a regulatory hormone called hepcidin
Hepcidin remains elevated for ~24 hours after a dose
Elevated hepcidin blocks iron absorption from subsequent doses
For this reason:
Single daily doses are generally better absorbed than split doses
Taking iron multiple times per day can reduce overall absorption
My clinical approach: cycling iron
In practice, I often recommend:
3 weeks of iron supplementation
Followed by 1 week off
This planned break allows the body to reset iron regulation, improves tolerance, and reduces prolonged suppression of absorption pathways. While this exact cycle hasn’t been directly studied in trials, the underlying mechanism — avoiding continuous hepcidin elevation — is well supported in the research.
Choosing the right form
Tolerance matters just as much as absorption. Some forms of iron are gentler on the gut than others.
General principles:
Liquid and powdered forms are often better tolerated than tablets
Some chelated or complexed forms are less constipating
Food-based iron may suit people sensitive to standard supplements
As a general guide for absorption:
liquid > powder > capsule > tablet
Co-factors that support iron use
Iron doesn’t work alone. Nutrients that support iron utilisation include:
Vitamin C (enhances non-heme iron absorption)
Vitamin B12 and folate (required for red blood cell production)
Vitamin A (helps mobilise stored iron)
Copper (needed for iron transport)
Low levels of these can limit response to iron supplementation.
What to avoid around dosing
Iron absorption is reduced when taken alongside:
Coffee or tea
Calcium supplements or high-calcium meals
Antacids or acid-suppressing medications
Spacing iron away from these by 1–2 hours can improve effectiveness.
Next step: In the final blog, I unpack why inflammation and a hormone called hepcidin can completely block iron absorption — even when you’re doing everything “right”.