Letters to the Editor

The Role of Vitamin C in the Treatment of the Common Cold

to the editor: The authors of “Treatment of the Common Cold,” in American Family Physician, stated that vitamin C is not recommended for active treatment of the common cold.1Their recommendation was based on a Cochrane review that I coauthored.2

The Cochrane review was limited to placebo-controlled trials in which at least 0.2 g of vitamin C was used per day.2 Most of these trials examined vitamin C administration as regular supplementation and provided strong evidence that vitamin C shortens the duration of colds and alleviates its symptoms. Children benefited more than adults.2 The data also suggested that high doses of vitamin C are more beneficial than low doses.2–6

Stratification of the regular supplementation trials in children by vitamin C dosage shows a tendency for dose dependency. Four trials, using 0.20 to 0.75 g of vitamin C per day, found an average reduction of 7 percent in common cold duration (95% confidence interval [CI], −19 to 5). Six trials with 1 g of vitamin C per day found an average reduction of 18 percent (95% CI, −32 to −3), and two trials using 2 g of vitamin C per day found an average reduction of 25 percent (95% CI, −50 to 0.1). Therefore, the 13.6 percent estimate for common cold reduction we calculated in the Cochrane review2, based on all 12 trials with children who received at least 0.2 g of vitamin C per day, may underestimate the effect of high doses.

Although the regular supplementation trials demonstrate that vitamin C has physiologic effects on the common cold, taking supplements throughout the year to slightly shorten colds does not seem reasonable. Consequently, therapeutic vitamin C supplementation soon after the onset of cold symptoms seems more rational. Few trials have been conducted, and results are not consistent; methodologic variation partially explains the divergence in results.2,5,6

The only trial that compared regular and therapeutic supplementation was conducted in adults.3 The researchers administered 3 g of vitamin C per day and found no difference between regular and therapeutic supplementation.3–5 Furthermore, they found that 6 g of vitamin C per day was associated with twice as much benefit as the 3 g per day dose.3–5 Because no trials have been conducted in children, our review concluded that such trials are warranted.2

Although there is no direct evidence to show that therapeutic vitamin C would affect colds in children, and therapeutic trials with adults are only partly positive,2–6 it may still be reasonable to suggest testing vitamin C to treat colds. The results of a controlled trial are an average for a group. Vitamin C is inexpensive and safe, and its effect on an individual may be much more (or much less) than the benefit suggested by a single trial, or by the pooled results of a meta-analysis.6

Send letters to Kenny Lin, MD, Assistant Editor, American Family Physician, e-mail: afplet@aafp.org , or 11400 Tomahawk Creek Pkwy., Leawood, KS 66211-2680.

Please include your complete address, e-mail address, telephone number, and fax number. Letters should be fewer than 500 words and limited to six references (including citation of original article) and one table or figure.

Letters submitted for publication in AFP must not be submitted to any other publication. Possible conflicts of interest must be disclosed at time of submission. Submission of a letter will be construed as granting the American Academy of Family Physicians permission to publish the letter in any of its publications in any form. The editors may edit letters to meet style and space requirements.

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