Vitamin C reduces the severity of common colds: a meta-analysis
BMC Public Health, doi:10.1186/s12889-023-17229-8
Background Randomized trials have shown that vitamin C shortens the duration of common colds. Some trials reported greater effects on severe cold symptoms compared with mild symptoms. This review systematically compares the effects of vitamin C on severe and mild common cold symptoms. Methods We included all placebo-controlled trials of orally administered vitamin C in doses of at least 1 g/day for the common cold for people in good health at baseline. The analysis was restricted to trials which reported both the total duration of the common cold, and the severity of the common cold measured using severity scales, the duration of more severe stages of the cold, or proxies for severe colds such as days indoors. Findings were pooled using the inverse variance, fixed effect options of the metacont function of the R package meta to calculate the ratio of means estimate.
Results Fifteen comparisons from 10 trials which reported both mild and severe symptoms were identified. All trials were randomized and double-blind. Compared to placebo, vitamin C significantly decreased the severity of the common cold by 15% (95% CI 9-21%). The direct comparison of the effect of vitamin C on mild and severe symptoms was limited to five comparisons which found that vitamin C had a significant benefit on the duration of severe symptoms. In this subset, there was a significant difference in the size of the effect of vitamin C on the overall duration of colds versus the duration of severe colds (P = 0.002), and vitamin C had no significant effect on the duration of mild symptoms.
Conclusions The common cold is the leading cause of acute morbidity and a major cause of absenteeism from work and school. However, absenteeism is dependent on the severity of symptoms. The finding that vitamin C may have a greater effect on more severe measures of the common cold is therefore important. Further research on the therapeutic effects of vitamin C on the common cold should measure outcomes of differing levels of severity.
Supplementary Information The online version contains supplementary material available at https://doi. org/10.1186/s12889-023-17229-8. Supplementary Material 1: Search for the trials, Figs. S1-S5, Description of the included trials. Supplementary Material 2: Spreadsheet describing the calculations.
Authors' contributions HH planned the study, collected the data, carried out the statistical analysis and wrote the draft manuscript. EC confirmed the collected data and participated in the revision of the manuscript. Both authors read and approved the final manuscript.
Funding No external funding. Open Access funding provided by University of Helsinki (including Helsinki University Central Hospital).
Data availability All data generated or analysed during this study are included in this published article and its supplementary information files.
Declarations Ethics approval and consent to participate Not applicable. This is a systematic review of studies already published.
Consent for publication Not applicable.
Competing interests The authors declare no competing interests.
Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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