Vitamin C will not prevent colds but may provide some relief

In 1970, the chemist Linus Pauling published a book titled Vitamin C and the Common Cold, in which he advised taking large daily doses of this nutrient to achieve optimal health, especially against colds. Pauling is one of only five people to have won two Nobel prizes, and the only person to have won both alone. Today the idea of taking vitamin C to ward off colds is accepted as common knowledge, to the extent that even cold remedies from the pharmacy include it. All this, one supposes, should be sufficient guarantee, but does it really work?

Pauling learned of the added benefits of vitamin C — also known as ascorbic acid — in 1966 from the biochemist Irwin Stone, who had experimented with this compound as a food preservative. Vitamin C has been known since 1912 to prevent scurvy, a typical disease suffered by sailors on long voyages. Stone was responding to an earlier idea that mega-doses of vitamins was the secret to health and longevity. Pauling went further and incorporated this hypothesis into what he called orthomolecular medicine, based on dietary supplements in large doses.

It is worth clarifying that neither of these ideas is related to Pauling’s two Nobel Prizes. He won the Chemistry prize in 1954 for his work on molecular bonds; and the Nobel Peace Prize was awarded to him in 1962 for his anti-nuclear activism. After these moments of glory, Pauling’s views were met with skepticism: in his book, he recommended taking at least 2.3 grams of vitamin C a day, the equivalent of eating more than 30 oranges.

Since then, megavitamin therapy and orthomolecular medicine have failed to gain traction within the scientific community, due to the lack of solid evidence. With regard to vitamins in general, the current view is that excessive doses are harmful in the case of fat-soluble vitamins, such as A and E, which accumulate in adipose tissue, while excessive doses in the case of water-soluble vitamins, such as C, are irrelevant because the excess is eliminated.

A glut of vitamins is bad

Even when administered in moderate doses, the benefits of multivitamins are “limited,” according to Neal Barnard, professor of medicine at George Washington University. The last major study to date, involving nearly 400,000 people from 2024, has not found that these supplements extend life; on the contrary, they are associated with slightly higher mortality. Remarking on the study, Barnard and his team point out that “there is little health rationale for the use of multivitamin supplements.”

The experts say that these micronutrients should be consumed as part of a healthy diet that provides the recommended amounts — about 0.1 grams per day for vitamin C — and that they should only be supplemented under medical prescription should there be a deficit. An excess of vitamin C can be harmful in people with kidney problems, undergoing cancer treatments or those with certain diseases. High doses may also cause diarrhea.

However, Barnard and his colleagues do not rule out the possibility that supplementing a particular vitamin may provide benefits in specific cases — for example, a multivitamin may help to boost memory in the elderly and folic acid during pregnancy helps the healthy development of the fetus. Vitamin C is an antioxidant that is said to have the ability to boost the immune response. Could it be useful in helping fight colds?

Limited usefulness

At the Department of Public Health, University of Helsinki, Finland, biochemist and physician Harri Hemilä analyzes the potential benefits of vitamin C and publishes reviews in the prestigious Cochrane Library, considered the standard of excellence in meta-studies, which synthesize data from a collection of studies. “There is strong evidence that normal people cannot prevent colds with vitamin C,” Hemilä says. “The exception is in people with very intense physical activity, such as marathon runners, for whom vitamin C can prevent half of all colds. Those who take very little in their diet would also benefit, “but such low levels of intake are not common,” he adds.

As for reducing the duration of a cold or its symptoms, studies show that vitamin C reduces the severity by up to 15%, although this refers to regular intake of a supplement of 1 gram per day or more, according to Hemilä. “However, adults tend to have a couple of colds a year, so it doesn’t seem reasonable to take vitamin C regularly,” he notes. But, although there is conflicting evidence regarding its benefits [when we already have a cold], taking a high dose of up to 10 grams a day could help bring some relief.

In short, Pauling overestimated the benefits of vitamin C, but there is something to his claims: it is not a panacea against colds but it is not a simple placebo either. It does not prevent, but it can to some extent relieve the effects of the virus. Hemilä believes more studies are needed and that current medicine harbors a prejudice against vitamin C, based on certain old and flawed studies that were reacting against Pauling’s theories.

Hemilä offers an alternative recommendation for colds: zinc. “The problem is that there are no good zinc pills in pharmacies, many have citric acid or too low a dose of zinc,” he says. Of course, too much zinc also has its risks, so any supplement should be taken on a doctor’s recommendation.

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