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. 2000;(2):CD000980.
doi: 10.1002/14651858.CD000980.

Vitamin C for Preventing and Treating the Common Cold


Vitamin C for Preventing and Treating the Common Cold

R M Douglas et al. Cochrane Database Syst Rev. .

Update in

  • Vitamin C for preventing and treating the common cold.
    Douglas RM, Hemila H, D'Souza R, Chalker EB, Treacy B. Douglas RM, et al. Cochrane Database Syst Rev. 2004 Oct 18;(4):CD000980. doi: 10.1002/14651858.CD000980.pub2. Cochrane Database Syst Rev. 2004. PMID: 15495002 Updated. Review.


Background: The role of oral ascorbic acid (vitamin C) in the prevention and treatment of colds remains controversial despite many controlled trials. There have also been a number of efforts to synthesize and/or overview the results of these trials, and controversy over what these overviews tell us.

Objectives: The objective of this review was to answer the following two questions: (1) Does regular high dosage supplementation with vitamin C reduce the incidence of colds? (2) Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect?

Search strategy: This review currently deals only with published trials from two previously published reviews by Kleijnen 1989 and Hemila 1992.

Selection criteria: Randomised and non-randomised trials of vitamin C taken to prevent or treat the common cold.

Data collection and analysis: Two reviewers independently extracted data and assessed trial quality.

Main results: Thirty trials were included. The quality of the included trials was variable. Vitamin C in doses as high as one gram daily for several winter months, had no consistent beneficial effect on incidence of the common cold. For both preventive and therapeutic trials, there was a consistently beneficial but generally modest therapeutic effect on duration of cold symptoms. This effect was variable, ranging from -0.07% to a 39% reduction in symptom days. The weighted difference across all of the studies revealed a reduction of a little less than half a symptom day per cold episode, representing an 8% to 9% reduction in symptom days. There was no clear indication of the relative benefits of different regimes or vitamin C doses. However in trials that tested vitamin C after cold symptoms occurred, there was some evidence that a large dose produced greater benefits than lower doses.

Reviewer's conclusions: Long term daily supplementation with vitamin C in large doses daily does not appear to prevent colds. There appears to be a modest benefit in reducing duration of cold symptoms from ingestion of relatively high doses of vitamin C. The relation of dose to therapeutic benefit needs further exploration.

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