Does vitamin C (ascorbic acid) increase the absorption of iron?

Does Vitamin C Increase Iron Absorption?

Yes, vitamin C (ascorbic acid) is the most potent enhancer of non-heme iron absorption and plays an essential physiological role in dietary iron uptake. 1, 2

Mechanism and Clinical Significance

Vitamin C dramatically improves the bioavailability of non-heme iron (found in plant foods) which normally has poor absorption rates of only 1-15% compared to heme iron's 15-40%. 1 The enhancement effect is:

• Strongly dose-dependent with a logarithmic dose-response relationship 2
• Achieved by forming chelates with iron that prevent formation of insoluble compounds and by reducing ferric to ferrous iron 1
• Effective even in meals without known inhibitors, likely by preventing unavailable iron complex formation in the gastrointestinal lumen 2

Clinical Recommendations for Iron Deficiency

For patients at risk of iron deficiency or with documented deficiency, combining iron supplementation with vitamin C is recommended as Best Practice Advice by the American Gastroenterological Association. 1

Practical implementation:

• Minimum 80 mg of vitamin C should be taken with iron supplements on an empty stomach for optimal absorption 1
• Iron-rich foods should be consumed alongside vitamin C sources (citrus fruits, vegetables) according to CDC recommendations 1
• This is particularly critical for vegetarians and those on plant-based diets where non-heme iron predominates 1
• One small glass of unsweetened orange juice provides adequate vitamin C for this purpose 1

Critical Contraindication: Iron Overload Conditions

Patients with hemochromatosis or iron overload must completely avoid vitamin C supplements, as vitamin C accelerates iron mobilization and can cause life-threatening cardiac complications. 3, 1, 4

The European Association for the Study of the Liver explicitly states:

• Vitamin C supplementation should be avoided entirely during iron overload, especially during the induction/depletion phase 3, 4
• High-dose oral vitamin C can accelerate iron deposition and favor deterioration of heart disease in severe hemochromatosis 3
• In iron-overloaded thalassemia major patients, vitamin C supplementation caused acute cardiac deterioration due to iron mobilization from reticuloendothelial stores 3, 4
• Cardiac dysrhythmias and cardiomyopathy are the most common causes of sudden death in iron overload states, with vitamin C posing serious risk 4

Limited Exception for Hemochromatosis Patients

If vitamin C is absolutely necessary for other medical reasons in a patient who has completed iron depletion therapy and achieved target ferritin levels:

• Maximum 500 mg daily after physician discussion 3, 4
• Only applies to patients without cardiac complications 4
• Patients on iron chelation therapy must limit total vitamin C to ≤200 mg daily 4

Dietary Vitamin C in Hemochromatosis

Dietary sources of vitamin C do not require restriction, but:

• Fruit juices and citrus fruits should be consumed alone, not combined with iron-rich meals 3, 1
• This reduces non-heme iron absorption from the meal without requiring elimination of healthy fruits and vegetables 3

Evidence Quality Considerations

The enhancing effect of vitamin C on iron absorption from single meals is far more pronounced than from complete diets over time. 5 When iron absorption was measured from complete diets over 5 days rather than single meals, the vitamin C effect was less dramatic, though still statistically significant. 5 This may explain why some long-term supplementation studies showed negligible effects on iron balance. 6, 5

A 2023 meta-analysis found that the evidence quality for vitamin C co-intervention with iron was very low, with non-significant differences in hemoglobin or ferritin outcomes. 7 However, this should not override the well-established physiological mechanism and guideline recommendations, particularly given that the effect is so unequivocal in controlled studies that it must be considered essential for dietary iron absorption. 2

Common Pitfalls to Avoid

• Do not consume coffee within one hour of iron supplementation as it decreases absorption by 54% 1
• Tea, polyphenols, phytates (in bran), and calcium (in dairy) all inhibit iron absorption and should be separated from iron intake 1
• Taking iron in the morning is preferable due to lower hepcidin levels compared to afternoon 1
• If gastrointestinal side effects are intolerable with fasting administration, taking iron with food improves tolerability despite decreased absorption—this trade-off may be necessary for adherence 1