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Vitamin C Shortens Duration of the Common Cold: Results from a Meta-Analysis

2/26/2019 4:02:43 PM
Linus Pauling stated in the 1960s, in his book Vitamin C and the Common Cold, that vitamin C could prevent and treat the common cold. This idea spread globally, despite a lack of evidence base. Since that time, some clinical trials have indicated that vitamin C might decrease the incidence or the duration of the common cold. Still, whether or not vitamin C should be recommended for self-limiting upper respiratory tract infections remains controversial. Researchers, therefore, conducted a meta-analysis of the data in 2018.
Nine studies were included in the meta-analysis. They were all randomized, placebo-controlled trials of vitamin C given as a therapy for the common cold. Dosages of vitamin C ranged from 1 to 8 grams per day during illness. Some of the studies provided a preventive dosage of vitamin C and increased the dosage at the first sign of illness onset.
Results showed no significant findings for dosing vitamin C at the onset of illness when compared with placebo. Positive findings were only found when daily (preventive) vitamin C supplementation was augmented with therapeutic doses of vitamin C at the onset of illness. This combination shortened the duration of the common cold by about a half a day (mean difference [MD] = -0.56; 95% CI, -1.03 to -0.10; p = .02), shortened the time confined indoors by about 10 hours (MD = -0.41; 95% CI, -0.62 to -0.19; p = .0002), and reduced symptoms of chest pain, fever, and chills.
There was too much heterogeneity among studies to firmly recommend a dosage schedule. However, the authors of the meta-analysis did make a suggestion based on the available data. They recommended a small daily dose of vitamin C (no more than 1.0 gram per day) to boost immunity and a larger dose (usually 3.0 to 4.0 grams per day) at the onset of illness to support recovery from the common cold.
Vitamin C is an essential nutrient that concentrates in leukocytes and declines rapidly during infections or stress. Supplementation might improve the ability of the immune system to resist infection by boosting antimicrobial and natural killer cell activities. Although the evidence is still limited, the results of this meta-analysis suggest that vitamin C is most effective for the common cold when taken daily and increased at the onset of symptoms.
Ran L, Zhao W, Wang J et al. Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Res Int. 2018.

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