The Pharmaceutical Journal
Vol 279 No 7461 p64
21 July 2007

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Doses of vitamin C do not protect against common cold

Prophylatic use of vitamin C does not offer protection against the common cold in the general population but can reduce the duration of illness, a review suggests (Cochrane Database of Systematic Reviews 2007; issue 3)

Comparison of 30 trials including 11,350 participants showed the relative risk of developing a cold when taking prophylactic vitamin C (200mg per day or higher) to be 0.96 (95 per cent confidence interval 0.92–1.00). In terms of cold duration, consistent benefit was seen for patients taking vitamin C prophylactically (8 per cent reduction in duration for adults, 13.6 per cent for children). But analysis of studies involving vitamin C therapy initiated after the onset of cold symptoms revealed no significant differences in duration or severity between treatment and placebo.

In a separate analysis of six trials involving 642 participants exposed to periods of extreme physical or cold stress (including marathon runners and skiers), vitamin C prophylaxis reduced the common cold risk by half (relative risk 0.5, CI 0.38–0.66).