Taking large doses of vitamin C prevents and cures the common cold.

Linus Pauling had already won two Nobel Prizes when he turned his attention to vitamin C. Chemistry in 1954, Peace in 1962. His scientific credibility was essentially unmatched in the public eye. So when Pauling published Vitamin C and the Common Cold in 1970, arguing that megadoses, 1,000 milligrams or more daily, versus the then-recommended 60 milligrams, would prevent colds and perhaps even cure cancer, millions of people listened.

Pharmacies sold out of vitamin C tablets. Health food stores stocked bottles by the case. Physicians found themselves fielding questions from patients who had read Pauling's book, which stayed in print for years. The logic seemed intuitive enough: vitamin C supports the immune system, colds are an immune system failure, therefore more vitamin C equals fewer colds. The Nobel laureate said so.

The clinical trials disagreed. By 1975, a well-designed double-blind trial by Terence Anderson at the University of Toronto enrolled 3,500 subjects and found that megadose vitamin C did not reduce the incidence of colds. Subsequent Cochrane reviews, pooling data from dozens of trials, consistently found no preventive effect in the general population, though they did find a modest reduction in cold duration (roughly eight percent in adults) and some benefit in people under extreme physical stress, like marathon runners and military personnel in subarctic conditions.

Pauling did not accept these results. He spent the rest of his career, he died in 1994, promoting increasingly large doses of vitamin C and vitamin supplements generally, eventually claiming they could prevent cancer and extend lifespan. His later work, conducted at his own institute, was methodologically weaker than his earlier chemistry research and was not widely accepted by oncologists or epidemiologists.

The myth persists partly because vitamin C supplementation is safe in modest doses and because the cold-season timing of people starting supplements corresponds naturally with feeling better as colds run their course. Post hoc reasoning, I took vitamin C and got better, is difficult to dislodge with epidemiological data.

The genuine finding that did emerge from this era: vitamin C deficiency does impair immune function, and people with poor diets benefit from adequate intake. The leap from "deficiency is harmful" to "surplus is beneficial" was Pauling's error, and it was an error the public was primed to accept from a man whose chemistry credentials were impeccable, even when he stepped beyond chemistry's borders.