Contrary to the age-old belief that Vitamin C helps in preventing and treating colds, it has emerged that it has no such effects. Common cold is a precisely defined disease, yet the illness is familiar to most people as it is a major cause of visits to a doctor and of absenteeism from work and school. It is usually caused by respiratory viruses for which antibiotics are useless. Since vitamin C was isolated in the 1930s it has been proposed for respiratory infections, and became particularly popular in the 1970s for the common cold when Linus Pauling drew conclusions from earlier placebo-controlled trials of large dose vitamin C on the incidence of colds. However, the role of vitamin C in the prevention and treatment of the common cold has been a subject of controversy for nearly six decades. There exist two conflicting views on the effectiveness of vitamin C as a cure for common cold. After collating the results of 30 published studies involving 11,350 people who took at least 200 milligrams of vitamin C each day, it has been found that for the average person, popping vitamin C pills is unlikely to ward off common cold or shorten its length or severity. However, for people exposed to short bouts of extreme physical exercise or cold temperatures, vitamin C can markedly reduce their risk of catching a cold. In six trials involving a total of 642 marathon runners, skiers, and soldiers taking part in sub-arctic exercises, vitamin C supplements reduced the risk of the common cold by 50 percent. Even for its therapeutic properties, Vitamin C has failed to provide successful results. Trials of high-dose vitamin C taken after the onset of cold symptoms showed no consistent effects on either the length of a cold or the severity of symptoms. But there were only a few of these therapeutic trials and their quality varied. One trial showed a borderline benefit from taking an 8-gram dose of vitamin C at the beginning of a cold, and two trials using 5-day supplementation reported benefits. Except individuals exposed to short periods of extreme physical stress, it is senseless for most people to take vitamin C every day to reduce their risk of catching a cold. The failure of vitamin C supplements to prevent colds in normal people indicates that routine high-dose prophylaxis is not justified for routine use. However, there is evidence that it could be justified in people exposed to brief periods of severe physical exercise or cold environment.
The Cochrane Library,
July 2007