Vitamin C Won't Prevent Colds, But May Modestly Shorten Severe Symptoms

American chemist Linus Pauling won two Nobel Prizes: chemistry in 1954 for chemical-bond research, and peace in 1962 for opposing nuclear weapons testing. Though not a dietitian or infectious disease physician, he published a book in 1970 urging 1,000-2,000 milligrams of vitamin C daily for good health, and more to prevent colds, credited with a surge in vitamin C sales that continues today. His advice relied partly on one placebo-controlled trial of children at a Swiss Alps ski camp; his interpretation was later criticised for mathematical errors and reliance on poor-quality trials.

Later evidence is more modest. A 2023 meta-analysis of ten placebo-controlled trials, covering 2,736 healthy adults, children and athletes taking at least 1,000mg of vitamin C daily, found a 15% reduction in severe cold symptoms, measured as days confined indoors, but no effect on mild symptoms' duration. A 2013 meta-analysis found lower doses of about 200mg a day did not reduce colds in the general population, though athletes and army personnel caught fewer; regular supplementation still cut symptom severity by 8-14% in children and adults. Taking vitamin C only after symptoms started had no benefit in either analysis.

Together, the two meta-analyses show no evidence that vitamin C lowers the chance of catching a cold, but some evidence it shortens severe symptoms by roughly 10% on average. That means five days of severe symptoms would shrink by about 12 hours, and a 24-hour bout would shorten by about two-and-a-half hours.

Pauling's recommended dose sits near today's upper safety limits: 2,000mg a day for US adults, with Australian guidelines advising against exceeding 1,000mg daily, far above the 45mg recommended daily intake for adults, found in half an orange. Taking over 1,000mg a day long-term can cause gastrointestinal effects, raise kidney-stone risk, worsen iron absorption in people with undiagnosed haemochromatosis, and interact with radiation therapy, chemotherapy and statins. Fewer than 4% of Australians are deficient in vitamin C.