According to Linus Pauling, two-time Nobel laureate and the world's foremost vitamin C proponent, the vitamin's versatility in illness prevention arises from its role in the manufacture of collagen, the protein that gives shape to connective tissues and strength to skin and blood vessels.

One of the great misfortunes of human evolution, Pauling explained, was when human ancestors lost their ability to produce vitamin C.
Pauling believed the trait was probably discarded at a time when human ancestors had a diet of vitamin-rich plants and didn't need to produce the vitamin themselves.
This left today's primates, including humans, as one of the few groups of animals that must get the vitamin through the diet.

Ever since proto-humans moved out of fruit-and-vegetable-rich habitats, Pauling said, they have suffered great deficiencies of vitamin C.

Pauling said vitamin C consumption should be on par with what other animals produce by themselves, typically 10-12 grams a day.

In 1970 Linus Pauling published a book “ Vitamin C and The Common Cold “.
The book was a bestseller and led many people to believe in the value of the vitamin C for cold prevention and treatment.

An article in PLoS Medicine reviewing all of the best clinical research on this topic, suggests that the public's enthusiasm for the vitamin C may be unjustified.

Robert M Douglas of the Australian National University, Canberra, and Harri Hemilä of the University of Helsinki, Finland, reviewed the best quality studies on vitamin C and the common cold done over the last 65 years. All of these studies compared a daily dose of 200mg of vitamin C or more against placebo.

Did vitamin C given for prevention reduce the risk of picking up a cold ?

The authors looked at 23 studies done in the general population, using doses of up to 2g daily, and found that vitamin C did not reduce the risk.

They conclude that " the lack of effect of prophylactic vitamin C supplementation on the incidence of common cold in normal populations throws doubt on the utility of this wide practice."

In these prevention studies, those people who were given vitamin C and then caught a cold experienced a small reduction in the duration of the cold compared with those taking a placebo. The authors say that the clinical significance of this minor reduction "is questionable, although the consistency of these findings points to a genuine biological effect."

But the authors did find evidence that the vitamin C could help prevent colds in people exposed to extreme physical exertion or cold weather.

They found six studies in which the vitamin or a placebo was given to marathon runners, skiers and soldiers exposed to significant cold and/or physical stress.
Those taking the vitamin experienced, on average, a 50% reduction in common cold incidence.
According to authors urge "great caution" in making generalizations from this finding in 6 studies that is mainly based on marathon runners.

What about vitamin C as a possible treatment for an established cold ?

The authors found seven trials, all in adults, evaluating whether vitamin C taken when their symptoms started would shorten the cold.
When they looked at all seven studies together, they found no benefit from taking the vitamin. But in one of the seven trials, patients took a single very high dose of the vitamin ( 8 g ) on the day their symptoms started and experienced a shorter illness compared with people who took a placebo pill.
The authors say that the results in this single trial are "tantalising and deserve further assessment."

Source: Public Library of Science, 2005


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