Does ascorbic acid (Vitamin C) enhance the absorption of ferrous sulfate (Iron supplement)?

Ascorbic Acid Enhances Ferrous Sulfate Absorption

Ascorbic acid (vitamin C) should be used at a molar ratio of at least 2:1 with ferrous sulfate to enhance iron absorption, as this combination significantly improves iron bioavailability, particularly in meals containing inhibitors of iron absorption. 1

Mechanism of Action

Ascorbic acid enhances iron absorption through several mechanisms:

• Forms a chelate with ferric iron at the acidic pH of the stomach
• Maintains iron solubility at the alkaline pH of the duodenum
• Reduces ferric (Fe³⁺) to ferrous (Fe²⁺) iron, which is more readily absorbed
• Counteracts the effects of dietary inhibitors of iron absorption 2, 3

Evidence-Based Recommendations

Dosing Guidelines

• The American Gastroenterological Association recommends ascorbic acid supplementation with oral iron at a molar ratio of at least 2:1 (e.g., 20 mg ascorbic acid to 3 mg iron) 1
• For meals with high levels of iron absorption inhibitors, a higher ratio of 4:1 may be necessary 3
• A case report showed that 3 mg of ascorbic acid daily along with ferrous sulfate improved hemoglobin and iron status in an infant who was previously resistant to oral iron supplementation alone 4

Clinical Applications

• Most beneficial for patients consuming:

  • Vegetarian diets (primarily nonheme iron) 5
  • Meals with high levels of iron absorption inhibitors 3
  • Diets low in heme iron sources (meat, fish, poultry) 2

• Particularly useful for:

  • Patients with malabsorption conditions
  • Patients after bariatric surgery 1

Important Considerations and Limitations

• The enhancement effect is more pronounced in meals containing inhibitors of iron absorption 3
• Ascorbic acid has less effect on insoluble iron compounds like ferric oxide or hydroxide 2
• The stability of ascorbic acid during food storage and preparation can be problematic 5, 3
• While single-meal studies show significant enhancement, some longer-term studies suggest the effect may be less pronounced over time 6
• Taking iron with food improves tolerability but decreases absorption; ascorbic acid can help offset this decrease 1

Practical Implementation

• Administer ascorbic acid simultaneously with ferrous sulfate for maximum benefit
• Consider natural sources of vitamin C (fruits and vegetables) consumed with iron-fortified foods 3
• For patients with persistent iron deficiency despite standard supplementation, adding ascorbic acid may improve response
• Patients with hemochromatosis should avoid vitamin C supplements 1

The evidence strongly supports that ascorbic acid enhances the absorption of ferrous sulfate, particularly in situations where iron bioavailability is compromised by dietary factors or gastrointestinal conditions.