Vitamin C and Colds

Does Vitamin C reduce the incidence of colds?

In 1970, twice Nobel prize winner Linus Pauling announced in Vitamin C and the Common Cold that taking 1,000 mg of vitamin C (ascorbic acid) daily will reduce the incidence of colds by 45% for most people, but that some people need much larger amounts. (The RDA for vitamin C is 60 mg/day; 100 mg/day for smokers.) The 1976 revision of the book, retitled Vitamin C, the Common Cold and the Flu, suggested even higher dosages.

Despite the popular belief that vitamin C can cure the common cold, the scientific evidence for this is limited. A few studies suggest that taking vitamin C supplements at the beginning of cold symptoms, or just after possible exposure, can shorten a cold or ward it off altogether. However, most studies conclude that vitamin C does not prevent or treat the common cold.

While vitamin C “is essential for the formation and maintenance of cartilage, bone and teeth, and is used in moderate amounts to promote the healing of wounds and during convalescence from prolonged illnesses . . . there is no evidence to support its use in preventing or treating the common cold,” says Dr. Warwick Carter in his book The Complete Family Medical Guide. “In one trial, 3000 Californian users of vitamin C supplements were followed for ten years and had the same rate of illness and death as a control group of nonusers.”

A study in the journal Public Library of Science Medicine also concluded there's no proof that high doses of vitamin C are effective in preventing colds or reducing symptoms. The study authors reviewed 55 studies dating from 1940 and 2004 that looked at how well doses of at least 200 mg per day of vitamin C prevented or treated the common cold when compared with a placebo.

Most of the time, vitamin C didn't keep people from catching colds. However, when people, especially children, took vitamin C before they became sick, the illness didn't last as long. Most studies showed that the vitamin didn't help people who waited until after the onset of symptoms to take vitamin C, although one large study found that already-sick patients who took 8,000 mg on the first day of their illness got better faster. One group of people did seem to benefit more than others: Marathon runners, skiers, and soldiers exposed to extreme cold or physical exertion got sick 50 percent less often when they took vitamin C as a preventive measure.

Dr. Warwick warns that excess vitamin C in the body from taking too many vitamin C supplements may have several unusual effects. These include “increased blood levels of estrogens which cause breast tenderness and menstrual period irregularities, increased risk of kidney stones, reduced adsorption of vitamin B12 and the development of pernicious anemia, and rebound scurvy in babies born to mothers who take too much vitamin C during pregnancy.”