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English

Don't rely on vitamin C to prevent colds

  • Moderate value
  • Evidence A
  • Saves money
  • Disputed
  • Free
  • Takes minutes
  • No willpower

In plain words

Taking vitamin C every day will hardly make you catch fewer colds, and starting it after you already have a cold works only some of the time. Taking it every day shortens one cold by about 8%, which is about half a day less misery; whether that is worth 300 to 500 CNY a year is for you to work out. Marathon runners and soldiers marching in cold regions are the exception: among them, the number who caught a cold was cut in half.

Cost

An effervescent tablet costs about 1 to 2 CNY, 300 to 700 CNY a year.

What you get

A Cochrane review pooled 29 controlled trials with 11,306 people. For ordinary people taking vitamin C every day, the number of colds is basically not reduced. The share who caught colds RR 0.97 (RR is the risk ratio; 1 means the two sides are the same). 95% CI 0.94–1.00 is the plausible range. For trials where people started it only after a cold began, the original text says “no consistent effect”: some trials showed an effect and some did not. In the same review, taking it every day over the long term shortened the time of cold misery by about 8% (adults, 95% CI 3%–12%) and by 14% in children (7%–21%). Marathon runners, skiers and soldiers marching in cold regions are the exception. In 5 trials with 598 people, about half as many caught a cold. Incidence RR 0.48 (95% CI 0.35–0.64). It looks like a good deal because it is cheap, tastes sweet and sour, and the claim that “vitamin C prevents colds” has been passed around for half a century

Notes

Dispute: in the same review, taking it every day does shorten the time of cold misery. Adults by about 8% (3%–12%), children by 14% (7%–21%). Worked out, that is about half a day less sick per cold. Marathon runners, skiers and soldiers marching in cold regions are the exception. In 5 trials with 598 people, about half as many people caught a cold (RR 0.48, 0.35–0.64). The great majority of people belong to neither of these two groups

Evidence grade
A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources
  1. 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

Translated from the Chinese original. Original book, section 6, tip 6. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer