As cold and flu season starts each year, people turn to both old and new ways of avoiding the common cold. Hand washing becomes a frequent habit, keeping a safe distance from those with sneezing, sniffles and coughs becomes a prime concern, and individuals line up for flu shots in drug stores, doctor’s offices and workplaces. Some people also take a daily dose of vitamin C in the hopes that this may protect them from catching a cold, but does the evidence suggest that vitamin C has a role to play in common cold prevention?
Several studies have investigated the use of vitamin C in the prevention of viral colds. Unfortunately, the results of these studies are a bit conflicting. One long term randomized trial in Japan studied the effect of 500 mg daily of vitamin C supplementation over a 5 year period. Individuals taking 500 mg of vitamin C were compared to participants taking 50 mg of vitamin C. This study found that 500 mg of vitamin C did significantly reduce the frequency with which participants caught a cold, though there was no effect on shortening the course or lessening the symptoms of those who did end up catching a cold.
However, a large meta-analysis of 29 different randomized controlled trials found no overall protective effect against the common cold. The meta-analysis looked at a total of 11,000 participants who were randomly assigned to take at least 200 mg of vitamin C. There was no increased benefit when only studies using at least 1 gram of vitamin C were looked at.
Interestingly, when particular subsets of patients, out of the total 11,000, were looked at a 50 percent decrease in catching the common cold became evident. This significant protective effect against the common cold was seen in a subgroup of study participants who were exposed to extreme cold and/or vigorous physical activity while taking vitamin C.
Overall, it appears that vitamin C may not be as helpful for cold prevention for the average user as was once thought. Individuals who enjoy intense exercise, such as marathon runners or bikers, and those frequently exposed to a very cold climate may benefit from daily Vitamin C. Otherwise, the majority of kids and adults may do best to save their time and money and instead focus on other proven methods of preventing the common cold.
Douglas RM, Hemilä H, Chalker E, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD000980.
Natural Medicines Comprehensive Database. Vitamin C (Ascorbic Acid) Monograph.
UpToDate Online. The common cold in adults: Treatment and prevention.