The review's authors, Robert Douglas of the Australian National University and Harri Hemila of the University of Helsinki, Finland, wrote that the "lack of effect of (preventive) vitamin C supplementation on the incidence of the common cold in normal populations throws doubt on the utility of this wide practice."

A bestselling book, "Vitamin C and The Common Cold," by Nobel Laureate chemist Linus Pauling, published in 1970, and several subsequent books popularized the notion that large doses of the vitamin (1000 mg or more) could reduce the incidence of colds by almost half. The government's recommended daily allowance for vitamin C is 60 mg.

Small Reduction in Duration

The review, published Monday in the journal Public Library of Science Medicine, considered studies that compared people taking vitamin C to those that took a dummy pill, or placebo.

Of 23 studies done on the general population of people taking daily doses up to 2 grams, there was no overall reduction in the risk of getting a cold. But those people taking vitamin C who did catch a cold did experience a small reduction in the duration of the cold compared to those who caught colds while taking the placebo.

The researchers said it is "questionable" whether the patients actually got any medical benefit from taking the vitamin, but "the consistency of these finding point to a genuine biological effect."

Marathon Runners, Skiers and Soldiers

Douglas and Hemila did find evidence that the vitamin could help prevent colds in people exposed to extreme physical exertion or cold weather in six studies involving marathon runners, skiers and soldiers.

In those subjects, those taking vitamin C had, on average, a 50 percent reduction in common colds. But the authors caution against changing health habits based on studies involving people as fit as marathon runners.

Some people also start pumping vitamin C at the first sniffle. The researchers looked at seven studies that considered whether a surge of the vitamin might cut the length of a cold and found that, taken together, they showed no effect.

However, they noted that in one of the studies, people took a very high dose of the vitamin (8 grams) on the day symptoms started and did experience a shorter illness compared with those who took an inactive tablet. The researchers said the results of the lone trial are "tantalizing and deserve further assessment."