When should I take ferrous sulfate for best absorption?

Optimal Timing for Ferrous Sulfate Administration

Take ferrous sulfate once daily in the morning on an empty stomach, at least 1–2 hours before eating, to maximize iron absorption. 1

Dosing Schedule and Frequency

• Once-daily dosing is superior to multiple daily doses because iron doses ≥60 mg trigger hepcidin elevation that persists for 24–48 hours, blocking absorption of subsequent doses by 35–45% and increasing gastrointestinal side effects without improving efficacy. 1, 2
• Morning administration is more effective than afternoon or evening dosing because serum hepcidin levels increase throughout the day, reducing iron absorption from doses taken later. 1, 2
• The standard dose is ferrous sulfate 200 mg (containing 65 mg elemental iron) taken once daily. 1, 3

Timing Relative to Food and Beverages

• Take iron on an empty stomach (1–2 hours before or after meals) to maximize bioavailability, as food consumed within 2 hours before or 1 hour after iron can reduce absorption by up to 50%. 4, 1
• Avoid coffee and tea for at least 1–2 hours after taking iron, as these are powerful inhibitors of iron absorption. 1, 5
• If gastrointestinal side effects are intolerable, taking iron with a small amount of food is acceptable, though this reduces absorption. 4, 1

Enhancing Absorption

• Co-administer 250–500 mg vitamin C (ascorbic acid) with each iron dose to enhance absorption by forming a soluble chelate and reducing ferric to ferrous iron, especially when transferrin saturation is low. 4, 1, 2
• Consuming iron with orange juice (containing ~90 mg vitamin C) can increase absorption approximately 4-fold compared to taking it with coffee or breakfast. 2
• Avoid taking iron with calcium-containing foods or supplements, as calcium significantly reduces iron absorption; separate these by 1–2 hours. 4, 5

Alternative Dosing Strategy for Intolerance

• Alternate-day dosing (every other day) with 100–200 mg elemental iron significantly increases fractional iron absorption compared to daily dosing and reduces gastrointestinal side effects while maintaining overall efficacy, though the initial rate of hemoglobin rise may be slower. 1, 6
• This approach is particularly useful when daily dosing causes intolerable symptoms. 1

Expected Response and Monitoring

• Hemoglobin should increase by approximately 1–2 g/dL within 2–4 weeks of starting therapy; failure to achieve at least a 10 g/L rise after 2 weeks strongly predicts treatment failure (sensitivity 90.1%, specificity 79.3%). 1, 3
• Continue iron therapy for 3 months after hemoglobin normalizes to fully replenish iron stores, resulting in a total treatment duration of approximately 6–7 months. 1, 3

Common Pitfalls to Avoid

• Do not prescribe multiple daily doses (e.g., twice or three times daily), as this increases side effects without improving absorption due to hepcidin-mediated blockade. 1, 6
• Do not take iron with meals containing meat, dairy, or calcium supplements unless gastrointestinal intolerance necessitates it. 4, 5
• Do not consume iron with coffee, tea, or calcium-rich beverages, as these dramatically reduce absorption. 1, 5
• Do not stop iron therapy when hemoglobin normalizes; continue for an additional 3 months to restore iron stores. 1, 3

When to Consider Intravenous Iron

• Switch to intravenous iron if oral iron causes intolerable side effects despite dosing adjustments, if ferritin fails to improve after 4 weeks of compliant therapy, or in conditions where oral absorption is impaired (active inflammatory bowel disease, post-bariatric surgery, celiac disease). 1, 3