What dose of ascorbic acid should be taken with ferrous fumarate to maximize iron absorption?

Ascorbic Acid Dosing with Ferrous Fumarate

Take 250–500 mg of ascorbic acid (vitamin C) with each dose of ferrous fumarate to maximize iron absorption. 1

Recommended Dosing Strategy

• The American Gastroenterological Association recommends approximately 500 mg of vitamin C with iron supplements to improve absorption, especially if taking with meals. 1
• The optimal molar ratio of ascorbic acid to iron is 2:1 in meals containing low to medium levels of absorption inhibitors (e.g., 20 mg ascorbic acid per 3 mg elemental iron), which translates to roughly 100–200 mg vitamin C for a standard ferrous fumarate dose. 2
• When absorption inhibitors are present at high levels (tea, coffee, calcium), ascorbic acid may need to be added at molar ratios exceeding 4:1 for maximum benefit, supporting the 250–500 mg recommendation. 2

Evidence Supporting Vitamin C Enhancement

• Clinical trials demonstrate that ascorbic acid increases iron absorption from ferrous fumarate by nearly 2-fold in children over 6 years of age (from 5.5% to 8.2% absorption when 25 mg ascorbic acid was provided with orange juice). 3
• In female blood donors, the combination of ferrous fumarate 200 mg daily with ascorbic acid 500 mg daily accelerated hemoglobin recovery to pre-donation levels in just 1 month, compared to 2 months with ferrous fumarate alone. 4
• Ascorbic acid enhances iron absorption more potently than other organic acids because it both reduces ferric iron to the more absorbable ferrous form and chelates iron to keep it soluble. 2

Practical Administration Guidelines

• Take ferrous fumarate with 250–500 mg vitamin C once daily in the morning on an empty stomach, 1–2 hours before meals. 1, 5
• If gastrointestinal side effects occur with empty-stomach dosing, taking ferrous fumarate with a small amount of food plus 250–500 mg vitamin C maintains reasonable absorption while improving tolerance. 1
• Avoid consuming tea, coffee, or calcium-containing foods within 1–2 hours of the iron dose, as these are powerful inhibitors that counteract even high-dose vitamin C enhancement. 1, 5

Dosing Frequency Considerations

• Once-daily dosing is superior to multiple daily doses because iron doses ≥60 mg elemental iron trigger hepcidin elevation lasting 24 hours, which blocks absorption of subsequent doses by 35–45%. 1, 5
• A standard ferrous fumarate tablet (325 mg) provides approximately 106 mg elemental iron—well above the 60 mg threshold—making twice-daily dosing counterproductive. 5
• If once-daily dosing causes intolerable side effects, alternate-day dosing (every other day) with vitamin C significantly increases fractional iron absorption while reducing gastrointestinal symptoms. 1, 5

Common Pitfalls to Avoid

• Do not assume that more vitamin C is always better beyond 500 mg per dose; the enhancement effect plateaus, and excessive ascorbic acid may cause gastrointestinal upset without additional iron absorption benefit. 2
• Do not take vitamin C-enhanced iron with dairy products, antacids, or proton-pump inhibitors, as these medications and foods override the absorption-enhancing effect of ascorbic acid. 1, 5
• Do not use multivitamin preparations as your vitamin C source for iron enhancement, as they typically contain insufficient ascorbic acid (often <100 mg) to meaningfully boost ferrous fumarate absorption. 5

Monitoring Response

• Check hemoglobin at 2 weeks after starting ferrous fumarate with vitamin C; an increase of ≥10 g/L predicts treatment success with 90% sensitivity. 1, 5
• Continue treatment for approximately 3 months after hemoglobin normalizes to fully replenish iron stores, maintaining the vitamin C co-administration throughout this period. 1, 5