How is oral iron absorption optimised, and what impairs it?

Optimise absorption: take iron on an empty stomach (or with vitamin C/orange juice); consider alternate-day dosing (improves fractional absorption and tolerability).

Impairs absorption: taking iron with calcium supplements, tea/coffee (tannins), antacids, or food; enteric-coated tablets are NOT preferred (they release iron beyond the main absorption site, reducing absorption).

Clinical relevance. Advising correct iron administration (avoiding calcium/tea, not enteric-coated) maximises absorption and treatment success.

More Detail

Optimising oral iron absorption

How iron is taken markedly affects how much is absorbed.

Improves absorption

• Take on an empty stomach (e.g. before meals) where tolerated.
• Vitamin C (ascorbic acid) / orange juice enhances absorption.
• Alternate-day dosing can improve fractional absorption and reduce side effects.

Impairs absorption

• Calcium supplements - calcium inhibits iron absorption, so take them at a different time.
• Tea and coffee (tannins/polyphenols), antacids/proton pump inhibitors, and food (phytates).
• Enteric-coated/modified-release tablets are NOT preferred - they release iron beyond the duodenum/upper jejunum (the main absorption site), reducing absorption.

Tolerability

• Side effects (nausea, constipation) are common; taking with food improves tolerance but reduces absorption - a balance is needed.