Can Vitamin C really cure the common cold?

The seas claimed title to the first 'clinical trial' conducted 260 years ago. In this seminal experiment, designed and executed by an academically untrained Briton intrigued by scurvy (James Lind, who later became a physician), it was unmistakably confirmed that citrus fruits rapidly cure scurvy, but acidic agents like vinegar or diluted sulphuric acid do not. It is with this background that vitamin C (ascorbic acid), the true antiscorbutic/anti-scurvy bioactive, emerges anew in relation to a perennially disputed use: prevention and/or treatment of the common cold.

Ascorbic acid (AA) enjoys widespread recognition as a purported 'cure' or treatment for colds. In a recent small US population survey among active cold sufferers (and after they had cleared their cold), about one-third stated that they would take vitamin C for the common cold, independent of how long the duration of the cold would be abbreviated.1

This was contrasted to Echinacea (23%), zinc lozenges (9%), and an antiviral drug (6%). A 1997 review of data from several controlled clinical trials among well-nourished occidental subjects found AA supplementation (Ž 1 gram daily; over 2-9 months duration) to be equal to placebo.2 This contrasted to studies where physically stressed or undernourished individuals did show a favourable response to AA supplementation.2,3

A 2005 Cochrane review of the efficacy of AA in prevention or treatment of the common cold assessed 55 unique controlled clinical trials from 36 distinctive research publications, with a minimum daily dose of 200mg, and up to 8g.4 As observed above,2 the reviewers did not find any benefit of AA supplementation in the prophylaxis of colds but did assert that it may indeed be of utility among individuals undergoing intensive physical exercise or cold exposure stress.4

The review did find among persons engaged in routine AA supplementation (to prevent a cold) a clinically significant reduction in the duration of morbidity (symptomatic days) over a year: from 12 to 11 days for adults and from 28 to 24 days for children. In contradistinction, use of AA therapeutically (at the onset of a cold) was not found to abbreviate the duration or severity of colds.

A study conducted in Japan among inhabitants within a region of high gastric cancer incidence appears to be the longest chronic supplementation study to date that evaluated the impact of AA supplementation on colds.5 This controlled clinical trial enrolled subjects with diagnostically confirmed chronic atrophic gastritis.

After a run-in phase (starting in late 1995), where all subjects were given beta-carotene (BC; 15mg/day) and vitamin C (500mg/day) for four weeks, they were then randomised to one of four groups: 0 or 15mg/day BC and 50 or 500mg/day AA, for five years. The publication of a press release by the National Cancer Institute, declaring that the results from two NCI-sponsored clinical trials with BC yielded no benefit and suggested potential adverse effects,6 compelled the Japanese researchers to drop the BC arm. This left the sample size at 305 subjects, taking either the low- or high-dose AA, with 244 completing five years of supplementation. This revised protocol provided cold data for 3.5 years, captured by subjective reporting from each of the subjects four times yearly.

The average dietary intake of AA was found to be 150mg/day in this population. When the researchers defined a common cold as occurring three or more times during the survey period, a 66 per cent reduction in risk was seen in the high-dose group, and 72 per cent reduction when defined as four or more colds. Interestingly, no impact of high-dose AA was seen on the duration of colds. Moreover, the duration of runny nose was significantly longer in the high-dose group.

In toto, these data suggest that chronic ascorbic acid supplementation can effect a positive change in morbidity associated with the common cold, perhaps exerted through augmented immunovigilance.

1. Barrett B, et al. Using benefit harm tradeoffs to estimate sufficiently important difference: the case of the common cold. Med Decis Making 2005; 25:47-55.
2. Hemila H. Vitamin C intake and susceptibility to the common cold. Br J Nutr 1997; 77:59-72.
3. Hemila H. Vitamin C and common cold incidence: a review of studies with subjects under heavy physical stress. Int J Sports Med 1996; 17:379-83.
4. Douglas RM, et al. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2005; 4.
5. Sasazuki S, et al. Effect of vitamin C on common cold: randomized controlled trial. Eur J Clin Nutr doi: 10.1038/sj.ejcn.1602261.
6. Anonymous. Beta Carotene and Vitamin A Halted in Lung Cancer Prevention Trial (press release). Washington, DC: US National Cancer Institute. Jan 18, 1996.

Anthony Almada, MSc, is president and chief scientific officer of IMAGINutrition Inc. Respond: [email protected]

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