Does vitamin C help alleviate symptoms of viral infections, such as the common cold?

Vitamin C for Viral Infections

Vitamin C may be worthwhile for individual patients to test on a therapeutic basis for reducing the duration and severity of common cold symptoms, though it does not prevent colds in the general population. 1, 2

Efficacy of Vitamin C for Common Cold

Regular Supplementation

• Vitamin C does not decrease the average incidence of colds in the general population 1, 3
• However, it has consistently shown effects on:
  • Shortening the duration of cold symptoms 1, 2, 4
  • Reducing the severity of symptoms 1, 2, 4
• Special populations: Vitamin C halved the number of colds in physically active people 4, 3

Therapeutic Use (after symptom onset)

• Results have been inconsistent when vitamin C is initiated after cold symptoms begin 3
• Dose-response relationship has been observed:
  • 6-8 g/day was twice as effective at reducing cold duration compared to 3-4 g/day 3
  • This may explain why some therapeutic studies with lower doses (3-4 g/day) showed negative results

Mechanism of Action

• Vitamin C concentrations in plasma and leukocytes rapidly decline during infections 5
• It contributes to:
  • Maintaining redox integrity of cells
  • Protection against reactive oxygen species generated during respiratory burst
  • Improved immune system components (antimicrobial and natural killer cell activities, lymphocyte proliferation) 5

Clinical Recommendations

Dosing

• For therapeutic use during a cold:
  • Consider 6-8 g/day for potentially greater efficacy 3
  • European Rhinologic Society recommends zinc lozenges (≥75 mg/day of zinc acetate or gluconate) started within 24 hours of symptom onset as more effective for reducing cold duration 2

Safety Considerations

• Vitamin C has a good safety profile and low cost 3
• Should be considered alongside other evidence-based treatments for common cold:
  • Paracetamol for symptom relief
  • NSAIDs for pain
  • Nasal saline irrigation
  • Adequate hydration and rest 2

Limitations and Caveats

• Despite consistent findings of benefit, the magnitude of effect varies considerably between studies 6
• The clinical significance may not be clearly inferred from all studies 6
• Antibiotics have no benefit for viral common colds and increase risk of adverse effects 2

Beyond the Common Cold

• Some evidence suggests vitamin C may have benefits for:
  • Pneumonia prevention in specific populations (not general population) 3
  • Pneumonia treatment (limited evidence) 3
  • COVID-19 and sepsis (conflicting results) 3

Given the consistent effect on reducing duration and severity of cold symptoms, along with its good safety profile and low cost, vitamin C at therapeutic doses (6-8 g/day) may be worth trying on an individual basis when cold symptoms begin.