Does vitamin C prevent colds, cancer, etc.?

Dear Cecil:

Linus Pauling and others speak of the marvelous curative powers of vitamin C. I take it myself with superstitious regularity and virtually never get a cold. Yet others say there isn't one shred of evidence that vitamin C prevents colds or any other disease. Your answer will be an inestimable service to mankind.

Cecil replies:

All in a day’s work, bubba. The evidence for megadoses of vitamin C is mixed. One researcher, using data from eight separate studies, concluded that vitamin C freaks averaged about one-tenth fewer colds per year than other people, and their colds lasted one-tenth less time. More recently, researcher Elliot Dick at the University of Wisconsin studied 24 subjects, eight of whom had been exposed to a cold virus. Eight of the others vitamin C, and the other eight received a placebo. After a week of living together, seven of the eight placebo patients had colds compared with six of the eight vitamin C patients. The difference was that the symptoms of the vitamin C patients, as indicated by the number of coughs, sneezes, nose blowings, and so on, were only half as severe. The study will be repeated, but so far things look promising.

As for vitamin C and cancer, the American Cancer Society issued guidelines suggesting that consuming C-rich foods might reduce the risk of certain types of malignancies. But once you have cancer, vitamin C won’t help. A study recently published by researchers at the Mayo Clinic decisively rejects the contention of Pauling and others that megadoses of vitamin C can cure cancer. In addition, too much C can cause undesirable side effects. If you must take supplements, don’t take more than 60-100 milligrams extra per day.

Send questions to Cecil via cecil@straightdope.com.

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