1. Cochrane Database Syst Rev. 2013 Jan 31;(1):CD000980. doi:
10.1002/14651858.CD000980.pub4.

Vitamin C for preventing and treating the common cold.

Hemilä H(1), Chalker E.

Author information: 
(1)Department of Public Health, POB 41, University of Helsinki, Helsinki,
Finland. harri.hemila@helsinki.fi.

Update of
    Cochrane Database Syst Rev. 2007;(3):CD000980.

BACKGROUND: Vitamin C (ascorbic acid) for preventing and treating the common cold
has been a subject of controversy for 70 years.
OBJECTIVES: To find out whether vitamin C reduces the incidence, the duration or 
severity of the common cold when used either as a continuous regular
supplementation every day or as a therapy at the onset of cold symptoms.
SEARCH METHODS: We searched CENTRAL 2012, Issue 11, MEDLINE (1966 to November
week 3, 2012), EMBASE (1990 to November 2012), CINAHL (January 2010 to November
2012), LILACS (January 2010 to November 2012) and Web of Science (January 2010 to
November 2012). We also searched the U.S. National Institutes of Health trials
register and WHO ICTRP on 29 November 2012.
SELECTION CRITERIA: We excluded trials which used less than 0.2 g per day of
vitamin C and trials without a placebo comparison. We restricted our review to
placebo-controlled trials.
DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data. We
assessed 'incidence' of colds during regular supplementation as the proportion of
participants experiencing one or more colds during the study period. 'Duration'
was the mean number of days of illness of cold episodes.
MAIN RESULTS: Twenty-nine trial comparisons involving 11,306 participants
contributed to the meta-analysis on the risk ratio (RR) of developing a cold
whilst taking vitamin C regularly over the study period. In the general community
trials involving 10,708 participants, the pooled RR was 0.97 (95% confidence
interval (CI) 0.94 to 1.00). Five trials involving a total of 598 marathon
runners, skiers and soldiers on subarctic exercises yielded a pooled RR of 0.48
(95% CI 0.35 to 0.64).Thirty-one comparisons examined the effect of regular
vitamin C on common cold duration (9745 episodes). In adults the duration of
colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%). In
children, 1 to 2 g/day vitamin C shortened colds by 18%. The severity of colds
was also reduced by regular vitamin C administration.Seven comparisons examined
the effect of therapeutic vitamin C (3249 episodes). No consistent effect of
vitamin C was seen on the duration or severity of colds in the therapeutic
trials.The majority of included trials were randomised, double-blind trials. The 
exclusion of trials that were either not randomised or not double-blind had no
effect on the conclusions.
AUTHORS' CONCLUSIONS: The failure of vitamin C supplementation to reduce the
incidence of colds in the general population indicates that routine vitamin C
supplementation is not justified, yet vitamin C may be useful for people exposed 
to brief periods of severe physical exercise. Regular supplementation trials have
shown that vitamin C reduces the duration of colds, but this was not replicated
in the few therapeutic trials that have been carried out. Nevertheless, given the
consistent effect of vitamin C on the duration and severity of colds in the
regular supplementation studies, and the low cost and safety, it may be
worthwhile for common cold patients to test on an individual basis whether
therapeutic vitamin C is beneficial for them. Further therapeutic RCTs are
warranted.

DOI: 10.1002/14651858.CD000980.pub4 
PMID: 23440782  [Indexed for MEDLINE]