Case: A 38-year-old presents for acute onset runny nose, cough, and fever for the last 3 days. Her children at home have a similar presentation. She believes that she has been managing her symptoms well with Tylenol and rest. The patient is up to date on her COVID and flu shots and was wondering if there was anything else she could have done to prevent her symptoms. She saw a commercial about vitamin C supplements boosting the immune system and was wondering about their efficacy. How would you respond?
Studies of Vitamin C
Linus Pauling, FRS, did a summary of four relatively small published studies of vitamin C and concluded that vitamin C supplementation helped prevent and lessen colds.1 He mentioned a placebo-controlled study of vitamin C with viral inoculation which did not show any effect. His overall conclusion of efficacy for vitamin C led to the widespread belief that vitamin C was a proven effective therapy to prevent and treat the common cold. Since then, multiple trials and studies have examined the effect of vitamin C on the prevention and treatment of colds.
Courtney Ibabao
The Cochrane Review conducted a meta-analysis comparing 29 placebo-controlled trials involving 11,306 participants.2 Criteria included vitamin C supplementation of 0.2 g-1 g/day to study its efficacy in preventing the common cold. The analysis showed that supplemental vitamin C did not significantly reduce the incidence of colds. However, there was a statistically significant 8% reduction in adults and 14% in children in the duration of colds. In terms of treatment, there was no evidence of vitamin C’s efficacy.
A 2001 study conducted a small double-blind, randomized control trial to evaluate large doses of vitamin C as treatment for the common cold.3 Volunteers were divided and instructed to take varying doses ranging from 1 to 3 g of vitamin C vs a placebo at the onset of cold-like symptoms. Subjects were expected to assess the duration and severity of their cold. The data showed no significant difference in the severity or duration of cold symptoms between small or large vitamin C doses or placebo.
Dr. Douglas S. Paauw
A more recent meta-analysis by Hemilä and Chalker looked at 10 placebo-controlled trials of vitamin C for the prevention and treatment of colds.4 The analysis showed a small 15% reduction in more severe cold symptoms.
Summary
While vitamin C is safe, there is no evidence for its ability to prevent the common cold. Although the Cochrane review and more a recent meta-analysis by Hemilä and Chalker demonstrated statistical significance in shortening the duration of symptoms, it was a minimal reduction with little clinical significance. .
Ms. Ibabao is a fourth year medical student at the University of Washington School of Medicine; Dr. Paauw is Professor of Medicine, Rathmann Family Foundation Endowed Chair Patient-centered Clinical Education, at the University of Washington School of Medicine, Seattle. They have no conflicts of interest.
References
1. Pauling L. The significance of the evidence about ascorbic acid and the common cold. Proc Natl Acad Sci USA. 1971;68:2678-2671.
2. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. 2013;1(1).
3. Audera C et al. Mega‐dose vitamin C in treatment of the common cold: a randomised controlled trial. Med J Australia. 2001;175(7):359-362.
4. Hemilä H, Chalker E. Vitamin C reduces the severity of common colds: a meta-analysis. BMC Public Health. 2023;23:2468.