Vitamin C Dosing with Ferrous Sulfate
Give 80-100 mg of vitamin C with ferrous sulfate, taken in the morning on an empty stomach for optimal iron absorption. 1
Recommended Dosing Strategy
The 2024 AGA Clinical Practice Update provides the most current guidance on this topic:
- 80 mg of ascorbic acid (vitamin C) taken with iron on an empty stomach has been shown in iron isotope studies to improve iron absorption 1
- 500 mg of vitamin C can be used if the patient needs to take iron with a meal containing calcium or fiber, as this higher dose allows iron absorption even in the presence of these inhibitors 1
The guideline explicitly states as Best Practice Advice #3: "Add vitamin C to oral iron supplementation to improve absorption" 1
Mechanism and Clinical Context
Vitamin C enhances iron absorption through two mechanisms:
- Forms a chelate with iron that prevents formation of insoluble iron compounds
- Reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is more readily absorbed 1
Important Caveats
The evidence for vitamin C is actually mixed. The 2024 AGA guideline acknowledges that "evidence supporting vitamin C administration to improve iron absorption is mixed, and further study is needed to clarify the effectiveness of this practice" 1. A 2020 randomized clinical trial of 440 patients found that oral iron supplements alone were equivalent to iron plus vitamin C (200 mg three times daily) in improving hemoglobin recovery 2. However, the guideline still recommends adding vitamin C based on mechanistic data and some positive absorption studies.
Practical Implementation
- Timing: Take in the morning on an empty stomach for best absorption 3
- Form: Can use vitamin C tablets or a glass of orange/citrus juice (which provides approximately 90-100 mg vitamin C) 4, 3
- Avoid: Do not take iron with coffee, tea, milk, or meals containing grains, as these markedly reduce absorption 1, 3
- Wait time: Avoid coffee or tea within 1 hour after taking iron 1
The afternoon dosing results in 37% lower iron absorption compared to morning dosing due to higher serum hepcidin levels 3.