Vitamin C and colds
Does not prevent colds in most people. Regular use slightly shortens them. People under heavy physical stress are the exception.
Education only, not medical advice. Talk to your clinician before starting a supplement, especially if you are pregnant, take medication or have a condition.
Evidence grade: C (A strong, B good with gaps, C limited or mixed, D early)
The Cochrane review
Across 29 trials and over 11,000 participants, regular vitamin C did not reduce how often the general population caught colds [1]. It shortened colds by about 8% in adults and 14% in children [1]. In five trials of people under heavy short-term physical stress, such as marathon runners and soldiers, it roughly halved cold risk [1]. Starting vitamin C after symptoms begin showed no consistent benefit [1].
Practical
The adult upper limit is 2,000 mg per day; higher intakes can cause diarrhea and may raise kidney stone risk in some people [2].
Sources
- Hemilä & Chalker 2013, Cochrane. doi.org/10.1002/14651858.CD000980.pub4
- NIH ODS, Vitamin C fact sheet. ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
DOIs verified against Crossref and official pages checked on 2026-10-15.