BAD news for fans of vitamin C: it is not the cold-buster it鈥檚 cracked up to be. In fact, regular doses will not prevent a cold in most people, though it might not last so long, according to a major review of existing research.
Robert Douglas of the Australian National University in Canberra and colleagues looked at 55 studies dating back 65 years. They conclude that regular doses of at least 200 milligrams of vitamin C do not reduce the risk of a cold in the general population.
The duration of any cold that did develop was shortened. 鈥淏ut only by about half a day in adults, and slightly more in children,鈥� Douglas says. The evidence that vitamin C helps treat an established cold is also very weak. Only one study, in which people were given a massive 8-gram dose on the first day of symptoms, found any effect (PLoS Medicine, vol 2, p e168).
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However, people experiencing extreme physical stress or cold do benefit from taking vitamin C in advance. Studies of skiers, soldiers and marathon runners suggest that regular vitamin C can slash their incidence of colds by half. 鈥淚t does seem there is a small subset of people who benefit, when for the general population it鈥檚 zilch,鈥� Douglas says.
