Don’t rely on vitamin C to prevent colds

Cost: Each effervescent tablet costs roughly 1–2 yuan; annual expense ranges from 300 to 700 yuan.
In plain terms: A combined analysis of 29 controlled trials involving 11306 participants shows that daily vitamin C intake hardly reduces the likelihood of catching a cold. Taking it after symptoms appear also yields inconsistent results. It can shorten the duration of a cold by about 8%, which equals roughly half a day of reduced discomfort. The absolute number of people who benefit from this effect is 500. Whether this half-day of relief is worth spending several hundred yuan per year is a personal calculation. Marathon runners and soldiers stationed in cold climates form the exception: among them, daily vitamin C intake cuts cold incidence roughly in half.
Benefit: Cochrane’s pooled analysis of 29 trials with 11306 participants indicates that regular vitamin C consumption does not meaningfully lower overall cold incidence; the risk ratio is 0.97 (95% CI 0.94–1.00). For trials where vitamin C was taken after cold onset, results varied widely — some showed benefit while others did not. Among participants who took it regularly, the average cold duration decreased by 8% in adults (95% CI 3%–12%) and 14% in children (7%–21%). Marathon runners, skiers, and soldiers in cold environments again represent the exception: five trials with 598 participants demonstrated that vitamin C intake reduced cold incidence by half (RR 0.48; 95% CI 0.35–0.64). Its perceived value stems largely from its low cost, pleasant taste, and the long-standing belief that vitamin C prevents colds.
Evidence grade: A
Sources:Hemilä H, Chalker E (2013). Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. https://doi.org/10.1002/14651858.CD000980.pub4
Notes: Controversy: The same review confirms that regular vitamin C intake does shorten cold duration — by 8% in adults (3%–12%) and 14% in children (7%–21%), equating to roughly half a day of reduced illness per cold episode. Marathon runners, skiers, and soldiers in cold climates remain the exception; five trials involving 598 subjects show a 50% reduction in cold incidence (RR 0.48; 95% CI 0.35–0.64). The vast majority of people do not fall into these categories.