What are the recommended doses of vitamin C (ascorbic acid) for treating viral infections?

Vitamin C Dosage Recommendations for Viral Infections

For viral infections, vitamin C supplementation of 2-3 grams per day is recommended during acute illness, with higher doses of 200 mg/kg/day (up to 6-8 g/day) potentially beneficial for severe respiratory infections. 1, 2

Standard Recommended Dosing for Viral Infections

• Daily maintenance dose: 50-100 mg/day for healthy adults 1, 2
• During active viral infection: 2-3 grams per day 1, 2
• For severe respiratory infections: Up to 200 mg/kg/day for 4 days 2

Dosing Based on Severity of Infection

Mild Viral Infections (Common Cold)

• Standard dose: 1-2 grams daily in divided doses 2, 3
• While vitamin C doesn't decrease the average incidence of colds in the general population, it has been shown to halve the number of colds in physically active people 3
• Regular vitamin C administration shortens cold duration, with dose-response effects observed at 6-8 g/day 3

Moderate Viral Infections

• Recommended dose: 2-3 grams daily in divided doses 1, 2
• Particularly beneficial for patients with conditions causing chronic oxidative stress (diabetes, heart failure, smoking, alcoholism, COPD) 1

Severe Viral Infections/Critical Illness

• High-dose therapy: 200 mg/kg/day (approximately 12-16 g/day for average adults) 2
• Administration route: Intravenous administration is preferred for severe infections as oral absorption is limited due to saturable intestinal transporters 1
• For severe respiratory infections, including viral pneumonia or ARDS, high-dose IV vitamin C has shown promising results 4

Evidence for High-Dose Vitamin C in Viral Infections

The strongest evidence supports high-dose vitamin C for:

1. Respiratory viral infections: Two controlled trials found a statistically significant dose-response relationship for common cold symptom duration with doses up to 6-8 g/day 3

2. Pneumonia prevention: Three controlled trials found vitamin C prevented pneumonia, and two trials showed treatment benefits for pneumonia patients 3

3. Acute respiratory distress syndrome (ARDS): Case reports show rapid resolution of virus-induced ARDS with high-dose IV vitamin C 4

4. Critical illness: During critical illness, IV administration is crucial as enteral uptake is unpredictable due to limited intestinal absorption and impaired gut function 1

Important Clinical Considerations

• Administration route matters: For severe infections, IV administration bypasses the limited intestinal absorption of oral vitamin C 1
• Monitoring: Plasma vitamin C measurement is not recommended during critical illness or severe inflammation due to difficulty in interpretation 1
• Safety: Doses below 1 gram daily are generally considered safe for most individuals 5
• Duration: For acute viral infections, continue supplementation throughout the illness and for several days after symptom resolution 2

Cautions and Contraindications

• Doses exceeding 1 g/day may have adverse consequences in some individuals 5
• For IV administration, vitamin C should be diluted with normal saline or glucose to minimize adverse reactions 2
• Patients with renal insufficiency require dose adjustments and monitoring

High-dose vitamin C therapy represents a potentially valuable adjunctive treatment for viral infections, particularly in severe cases where oxidative stress and inflammation are significant contributors to pathology.