Vitamin C Won't Prevent Colds in Most Adults

July 18, 2007

HELSINKI, Finland -- Although most people won't find vitamin C effective protection against colds, marathon runners can cut their risk by about 50% if they take at least 200 mg every day.

HELSINKI, Finland, July 18 -- Although most people won't find vitamin C effective protection against colds, marathon runners can cut their risk by about 50% if they take at least 200 mg every day.

This latest -- although probably not final -- word on vitamin C comes from a review published online in issue 3 of The Cochrane Library.

Pooled data from more than 11,350 participants in 30 trials found that the relative risk of catching a cold was 0.96 (0.92 to 1.00) for people who took prophylactic vitamin C, said Harri Hemil, Ph.D., M.D., of the University of Helsinki, a co-author of the review.

The finding suggests that it "doesn't make sense to take vitamin C 365 days a year to lessen the chance of catching a cold," he said.

But a subgroup of six trials that enrolled 642 long distance runners, skiers, and soldiers deployed in sub-arctic regions revealed that vitamin C supplementation reduced by half the risk of catching cold in those populations (RR 0.50, 95% CI 0.38-0.66).

Pooled data from 9,676 people who caught colds while taking the vitamin prophylactically did find that vitamin C reduced the duration of sneezing, congestion, and other cold symptoms by about 8% in adults (95% CI 3% to 13%) and by 13.6% in children (95% CI 5% to 22%).

Trials of high dose vitamin C initiated at the first signs of a cold demonstrated no consistent effect on either duration or severity of symptoms, but, Dr. Hemil said, there were few such trials in the literature and "their quality was variable."

Vitamin C has steadily gained status as a cold remedy since its discovery in the 1930s, but the mega-vitamin C movement took off in the 1970s when Nobel Prize-winning chemist Linus Pauling published his book, Vitamin C and the Common Cold. Pauling encouraged people to take 1,000 mg of vitamin C daily.

The first Cochrane Review of prophylactic vitamin C was published in 1998. That review was updated in 2004 and this latest update includes a single new study but no change in the Cochrane take on vitamin C.

Dr. Hemil said he sees little use in further study of the vitamin in colds for adults. However, he would like to see more studies on vitamin C and colds in children and vitamin C and pneumonia.

Vitamin C, he said in a statement, is not a panacea, but it is not useless either. "Pauling was overly optimistic, but he wasn't completely wrong."