Vitamin C for Cold Prevention
Cochrane meta-analysis: regular vitamin C (1+ g/day) fails to prevent colds generally, but in marathon runners, skiers, and soldiers in cold conditions it reduced incidence by ~50%. Duration is modestly shortened (~8% adults). Low-risk, low-cost, reasonable for active people.
Overview
Verdict
Vitamin C does not prevent colds in the general population but halves incidence in heavy exercisers and shortens colds ~8%.
How It Works
Dosing & Protocol
Typical dose
- Recommended dose
- 1 g/day regularly during high-risk periods.
- Expected timeframe
- Across a season for prevention effect.
Protocol
- form
- Ascorbic acid, or buffered ascorbate if stomach upset occurs; divided doses improve absorption above 200 mg
- duration
- Continuous regular use - starting it after symptoms begin has not shown consistent benefit
- co factor
- Take with food in divided doses. Evidence is mixed and unusually well characterised. The Cochrane review by Hemila and Chalker, covering 29 trials in 11,306 participants, found regular supplementation at 200 mg/day or more did not reduce the incidence of colds in the general population, but did shorten duration by about 8% in adults and 14% in children - roughly half a day off a typical cold. The clear exception is people under extreme physical stress: marathon runners, skiers and soldiers in subarctic conditions, where regular supplementation halved cold incidence.
- titration
- Up to 2,000 mg/day, which is the tolerable upper intake level for adults
- starting dose
- 200 mg/day taken regularly, if using it at all; higher doses of 1-2 g/day have been used in trials
Evidence
Vitamin C for preventing and treating the common cold
Hemila H, Chalker E
Regular vitamin C did not reduce cold incidence in the general population but shortened duration modestly
Safety
Caveats
Doses above 2 g/day cause loose stools. Starting vitamin C after symptoms begin does not help.
Less likely to help if
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Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.