Vitamin C won’t prevent most colds, but it may do one small thing

Supermarkets and pharmacies ramp up sales of vitamin C during the cold and flu season, despite a growing body of evidence that suggests it may not be effective in preventing most colds. The story of vitamin C's relationship with colds is complicated, with connections to a Nobel Prize-winning chemist, Linus Pauling, who published a book on the subject in 1970.

Pauling recommended high doses of vitamin C, around 1,000-2,000 milligrams a day, to maintain good health and potentially prevent colds. However, this advice has been widely criticized due to flawed analysis of studies he performed and analyzed.

Subsequent studies have shown that any potential benefits of vitamin C in preventing colds are minimal and only appear under certain circumstances, such as for athletes or individuals in the military. In fact, a 2023 meta-analysis of ten placebo-controlled trials involving 2,736 participants found that those who took vitamin C had a 15% reduction in severe cold symptoms, but this effect only lasted an average of 12 hours.

Regular vitamin C supplementation has been shown to reduce the severity of symptoms by 8-14% in both children and adults, but taking it at the onset of a cold has no effect. The recommended daily intake for vitamin C is lower than Pauling's suggested amount, with Australia recommending a maximum of 1,000mg per day and the United States allowing up to 2,000mg daily. While high doses of vitamin C can increase the risk of adverse events, less than 4% of Australians are vitamin C deficient.