What oral vitamin C supplement and dose is appropriate for a healthy 17‑year‑old female taking ferrous sulfate for iron deficiency?

Vitamin C Supplementation with Ferrous Sulfate for Iron Deficiency in a 17-Year-Old Female

For a healthy 17-year-old female taking ferrous sulfate for iron deficiency, co-administer 250–500 mg of vitamin C once daily in the morning on an empty stomach alongside the iron supplement to enhance absorption. 1

Recommended Iron Dosing Regimen

• Prescribe 60–120 mg elemental iron once daily (one 200 mg ferrous sulfate tablet contains 65 mg elemental iron; two tablets provide 130 mg) for adolescent females with confirmed iron deficiency or iron-deficiency anemia. 2
• Administer the iron supplement as a single morning dose on an empty stomach to maximize absorption. 1, 2
• Hemoglobin should increase by ≥1 g/dL (≥10 g/L) after 4 weeks of therapy if the regimen is effective; failure to achieve this rise warrants reassessment. 2
• Continue treatment for an additional 2–3 months after hemoglobin normalizes to fully restore iron stores, resulting in a total treatment course of approximately 6–7 months. 1, 2

Vitamin C Co-Administration Strategy

• Take 250–500 mg of vitamin C (as a tablet or 200 mL of orange juice) together with the iron supplement in the morning to enhance non-heme iron absorption. 3, 1, 4
• The vitamin C should be administered at the same time as the iron, not separately later in the day, because vitamin C forms a chelate with iron that facilitates absorption when both are present simultaneously in the gastrointestinal tract. 1, 4
• A recent 2024 meta-analysis found that vitamin C supplementation increased serum hemoglobin by only 0.14 g/dL (95% CI 0.08–0.20), a statistically significant but clinically marginal benefit. 5 However, in adolescents with lower baseline vitamin C intake, the effect may be more pronounced. 6

Substances to Avoid Around Iron Dosing

• Avoid food, tea, coffee, or calcium-containing products for at least 1–2 hours before and after taking iron, as these markedly reduce absorption. 1, 7, 4
• Food consumed within 2 hours of oral iron can reduce absorption by as much as 50%. 7
• Do not take iron with aluminum-based antacids or phosphate binders, as these inhibit absorption. 7

Alternative Dosing if Side Effects Occur

• If once-daily dosing causes intolerable gastrointestinal symptoms (nausea, constipation, abdominal discomfort), switch to alternate-day dosing with 100–200 mg elemental iron (one to two ferrous sulfate tablets every other day). 1, 2
• Alternate-day dosing significantly increases fractional iron absorption and reduces side effects while maintaining efficacy, because doses ≥60 mg trigger hepcidin elevation that persists for 24 hours and blocks absorption of subsequent doses by 35–45%. 1, 8
• A 2025 study demonstrated that patients receiving ferrous sulfate once daily achieved a hemoglobin increase of ≥1 g/dL at 2 weeks, whereas every-other-day dosing produced a slower initial rise (0.69 g/dL) but similar final outcomes at 3 months with fewer gastrointestinal side effects. 8

Monitoring and Follow-Up

• Check hemoglobin at 4 weeks to confirm adequate response; an increase of ≥1 g/dL indicates effective therapy. 1, 2
• Monitor blood counts every 6 months after completing therapy to detect recurrent iron deficiency. 1
• Assess menstrual blood loss, as menorrhagia is responsible for iron deficiency in 5–10% of menstruating adolescents and should be addressed as a potential primary cause. 2

When to Consider Intravenous Iron

• If hemoglobin fails to rise by ≥1 g/dL after 4 weeks despite confirmed adherence, transition to intravenous iron. 2
• Intravenous iron should also be considered if oral iron causes intolerable side effects despite dosing adjustments, or in cases of severe symptomatic anemia or chronic inflammatory conditions. 2

Common Pitfalls to Avoid

• Do not prescribe multiple daily doses of iron, as this increases side effects without improving absorption due to hepcidin-mediated blockade. 1, 7
• Do not discontinue therapy prematurely when hemoglobin normalizes; continue for 2–3 months to replenish iron stores. 1, 2
• Do not rely on multivitamin preparations as the sole source of iron, as they typically contain insufficient elemental iron (≤14 mg) for treating iron deficiency. 1
• Do not assume all gastrointestinal symptoms are due to iron; persistent symptoms warrant medical evaluation for other causes. 7