Letters to the Editor

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

Am Fam Physician. 2007 Oct 15;76(8):1111-1115.

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.26

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.35 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.35 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,26 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

Author disclosure: Nothing to disclose.

REFERENCES

1. Simasek M, Blandino DA. Treatment of the common cold. Am Fam Physician. 2007;75:515–20.

2. Douglas RM, Hemilä H, D'Souza R, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2004;(4):CD000980.

3. Karlowski TR, Chalmers TC, Frenkel LD, Kapikian AZ, Lewis TL, Lynch JM. Ascorbic acid for the common cold. A prophylactic and therapeutic trial. JAMA. 1975;231:1038–42.

4. Hemilä H. Vitamin C, the placebo effect, and the common cold: a case study of how preconceptions influence the analysis of results. J Clin Epidemiol. 1996;49:1079–84.

5. Hemilä H. Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit. Med Hypotheses. 1999;52:171–8.

6. Hemilä H. Do vitamins C and E affect respiratory infections? [Academic Dissertation] University of Helsinki, Helsinki, Finland, January 2006:21–7, 36–45, 48–9, 62–3. Accessed August 6, 2007, at: http://ethesis.helsinki.fi/julkaisut/laa/kansa/vk/hemila.

Send letters to Kenneth W. Lin, MD, MPH, Associate Deputy Editor for AFP Online, e-mail: afplet@aafp.org, or 11400 Tomahawk Creek Pkwy., Leawood, KS 66211-2680.

Please include your complete address, e-mail address, and telephone number. Letters should be fewer than 400 words and limited to six references, one table or figure, and three authors.

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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