How to Take Iron Supplementation
Take iron once daily in the morning on an empty stomach with 500 mg of vitamin C, and avoid coffee, tea, and calcium-containing foods for at least 1-2 hours. 1, 2
Optimal Dosing Strategy
Start with 50-100 mg of elemental iron once daily (equivalent to one 200 mg ferrous sulfate tablet containing 65 mg elemental iron, or one 324 mg ferrous fumarate tablet containing 106 mg elemental iron) 1, 2
Once-daily dosing is superior to multiple daily doses because iron doses ≥60 mg stimulate hepcidin elevation that persists for 24 hours and blocks absorption of subsequent doses 1, 2, 3
Consider alternate-day dosing (every other day) if side effects are problematic, as this significantly increases fractional iron absorption and may reduce gastrointestinal symptoms while maintaining efficacy 1, 2, 3
Timing and Administration
Take iron in the morning rather than afternoon or evening because hepcidin levels (which block iron absorption) are lower in the morning and increase throughout the day 2, 3
Take on an empty stomach when possible (1-2 hours before or after meals) to maximize absorption, though taking with small amounts of food is acceptable if gastrointestinal side effects are intolerable 1, 2, 4
Always take with 500 mg of vitamin C (ascorbic acid) to enhance absorption by converting ferric iron to the more absorbable ferrous form 2, 5
Critical Foods and Medications to Avoid
Do not consume coffee or tea within 1 hour of taking iron, as these are powerful inhibitors that can reduce absorption by up to 54% 2, 5
Separate iron from calcium-containing foods or supplements by 1-2 hours, as calcium significantly impairs iron absorption 2
Avoid taking iron within 2 hours of antibiotics, as iron interferes with antibiotic absorption 4
Do not take with fiber-containing foods, antacids, or phosphate binders at the same time, as these reduce iron absorption 2
Monitoring Response
Check hemoglobin at 4 weeks to assess response - you should see a rise of at least 10 g/L within 2 weeks if oral iron is working 1, 2
Continue treatment for approximately 3 months after hemoglobin normalizes to adequately replenish iron stores, not just correct anemia 1, 2
Monitor blood counts every 6 months after completing therapy to detect recurrent iron deficiency 1
Managing Side Effects
If standard daily dosing causes intolerable gastrointestinal symptoms (constipation, nausea, diarrhea), reduce to one tablet every other day rather than discontinuing therapy 1, 2, 4
Consider switching to a different iron formulation (ferrous gluconate or ferrous fumarate instead of ferrous sulfate) if one preparation is poorly tolerated 1, 2
Ferric maltol may be better tolerated in patients with inflammatory bowel disease or previous intolerance to traditional iron salts, though it is more expensive 1
When to Switch to Intravenous Iron
Consider IV iron if oral iron causes intolerable side effects despite dosing adjustments (alternate-day dosing, taking with food, switching formulations) 1, 2
Switch to IV iron if hemoglobin fails to rise after 2-4 weeks of adherent oral therapy, as absence of response strongly predicts treatment failure 1, 2
IV iron is preferred for patients with prior gastric surgery, inflammatory bowel disease, chronic kidney disease, or when blood loss exceeds the ability to replete iron orally 1, 2
Common Pitfalls to Avoid
Do not take iron more than once daily - this increases side effects without improving absorption due to hepcidin elevation 1, 2
Do not stop treatment when hemoglobin normalizes - continue for 3 months to replenish iron stores 1, 2
Do not assume all gastrointestinal symptoms are from iron - persistent symptoms warrant evaluation for other causes 2
Avoid enteric-coated formulations as they may improve tolerability but significantly decrease absorption 2
Never supplement with iron if ferritin levels are normal or high - this is potentially harmful and not recommended 1