The truth about Vitamin C - a review of the evidence

The truth about vitamin C - a review of the evidence

The bottom line:

  • Dozens of studies have demonstrated the immunomodulating and antiviral effects of vitamin C as well as its potential role as an antioxidant, protecting against oxidative stress in the event of infection.
  • Regular use of vitamin C can reduce the duration and severity of common cold symptoms.
  • Clinical studies have shown vitamin C can halve the incidence of common cold following periods of extreme physical exercise (50% reduction in the incidence of common cold in select population groups).

The case for taking vitamin C supplements has long been a topic of debate among doctors and scientists and yet, vitamin C supplements remain widely used in the general community. Here, we review the evidence on the benefits of vitamin C supplementation and debunk some myths about this commonly used vitamin.

Vitamin C gained great public interest in the 1970s after Nobel prize winner Linus Pauling released a book titled ‘Vitamin C and the Common Cold’. Following this, a number of clinical trials were conducted which produced conflicting results and some confusion regarding the benefits of vitamin C supplementation in treating the common cold(1,2).

Nevertheless, dozens of studies have demonstrated the immunomodulating and antiviral effects of vitamin C as well as its potential role as a physiological antioxidant, protecting against oxidative stress in the event of infection(2). As such, the mechanism by which vitamin C may provide a protective effect during infection remains highly physiologically plausible, but what proven clinical effect (if any) has been demonstrated in humans?

In 2013, a large systematic review was conducted to determine whether vitamin C supplementation (at a dose of 200mg per day or greater) reduced the severity, duration or incidence of common cold. In this review, an analysis of 29 placebo-controlled clinical trials involving 11,306 participants revealed that regular vitamin C supplementation on a daily basis did not significantly reduce the incidence of common cold in the general population (i.e. it did not change how often people caught colds). However, regular supplementation was shown to significantly reduce the duration of common cold symptoms by 14% in children and by 8% in adults. Regular supplementation also assisted in reducing the severity of common cold symptoms. Of particular significance was the benefit observed in clinical studies which assessed participants exposed to short periods of extreme physical stress (e.g. marathon runners, skiers and soldiers) in which an analysis of 598 participants taking regular vitamin C had a greater than 50% reduction in the incidence of common cold. That is, the risk of acquiring common cold in these circumstances was halved overall compared to those taking placebo(2).

The authors of this study went on to conclude that vitamin C supplementation may be beneficial for short term use for people who engage in severe physical exercise to help prevent the occurrence of common cold. They also suggested that it may be worthwhile for patients with acquired common cold to test the benefits of vitamin C in reducing the duration and severity of their symptoms given the consistency of improvement in severity and duration of common cold symptoms with regular supplementation(2).

In summary, the findings of this comprehensive review of the literature has shown that:

  • Regular use of vitamin C has a modest but clinically significant effect in reducing common cold duration and severity in both children and adults.
  • Vitamin C supplementation may have significant benefits in select populations who engage in intense physical activity, by reducing the incidence of common cold in the post-exercise period.

References:

  1. Pauling L. Vitamin C and the common cold. San Francisco: Freeman; 1970.
  2. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews [Internet]. 2013;. Available from: https://pubmed.ncbi.nlm.nih.gov/23440782