Is Vitamin C effective against the common cold?
Many take Vitamin C as a preventative and/or treatment for the common cold; however, its efficacy is subject to controversy. In an effort to resolve the controversy, Harri Hemilá, MD, PhD, from the Department of Biochemistry, University of Helsinki, Finland, and an Australian colleague conducted a meta-analysis of 72 trials. They published their findings on January 31 in the Cochrane Database of Systemic Reviews.
The authors explain that Vitamin C for preventing and treating the common cold has been a subject of controversy for 70 years. They note that the common cold is a major cause of physician visits in high-income countries and of absenteeism from work and school. There are more than 200 viruses that can cause the common cold symptoms including runny nose, congestion, sneezing, sore throat, cough, and sometimes headache, fever, and red eyes. Symptoms vary from person to person and cold to cold. Since the common cold is usually caused by one of the respiratory viruses, antibiotics are useless; therefore, other potential treatment options are of substantial public health interest.
The goal of the meta-analysis was to determine 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. (A meta-analysis is a compilation of data from a number of studies to assess the validity of the findings.) For the study, the investigators 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). They also searched the U.S. National Institutes of Health trials register and WHO ICTRP on 29 November 2012.
The authors excluded trials which used less than 0.2 gram per day of Vitamin C and trials without a placebo comparison. They restricted their review to placebo-controlled trials. Two review authors independently extracted data. They assessed the incidence of colds during regular supplementation as the proportion of participants experiencing one or more colds during the study period. They defined the cold’s duration as the average number of days of illness of cold episodes.
Included in the study were 29 trial comparisons involving 11,306 participants. The risk ratio (RR) of coming down with a cold while taking Vitamin C regularly over the study period was determined. In the general community trials involving 10,708 participants, the pooled RR was 0.97. Five trials involving a total of 598 marathon runners, skiers, and soldiers on subarctic exercises yielded a pooled RR of 0.48. A total of 31 comparisons examined the effect of regular Vitamin C on common cold duration (9745 episodes). In adults the duration of colds was reduced by 8% (3-12%) and in children by 14% (7-21%). In children, 1 to 2 grams/day of 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 (3,249 episodes). No consistent effect of vitamin C was seen on the duration or severity of colds in the therapeutic trials. The authors note that the majority of included trials were randomized, double-blind trials. (Randomization refers to giving half the study group a placebo; double-blind means that neither the study subjects nor the administrators of the medication are aware of who receives the placebo.) They noted that the exclusion of trials that were either not randomized or not double-blind had no effect on the conclusions.
The authors concluded that 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; however, Vitamin C may be useful for people exposed to brief periods of severe physical exercise (i.e., marathon runners and skiers). They explained that regular supplementation trials have shown that Vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that were carried out. They wrote: “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.”
Reference: Cochrane Database of Systemic Reviews