As winter approaches, aggressive marketing of vitamin C begins in pharmacies and supermarkets as a shield against colds. Although taking high doses of vitamin C during virus season is a deeply entrenched practice among the public, modern scientific research shows that its real efficacy is far more modest.
This popular belief traces its roots back to 1970, when American chemist and two-time Nobel laureate Linus Pauling published a dedicated book. Despite the fact that Pauling was neither a nutritionist nor an infectious disease specialist, he advised the public to take between 1,000 and 2,000 milligrams of vitamin C daily to maintain health and prevent colds. His claim relied on a placebo-controlled study conducted on children in the Swiss Alps, which scientists today consider methodologically flawed. Nevertheless, the book boosted vitamin C sales to unprecedented levels.
Do megadoses actually work? Large-scale meta-analyses conducted in 2013 and 2023, combining data from thousands of individuals, revealed that vitamin C does not reduce the risk of developing a cold. Furthermore, starting to take it after cold symptoms appear yields no therapeutic benefit whatsoever. The only minor benefit is observed when a person takes the vitamin regularly, even prior to illness — in this scenario, the duration of severe symptoms is reduced by an average of 10–15% (for instance, a 5-day severe cold might be shortened by 12 hours), though it has no effect on mild symptoms at all. The sole exceptions are professional athletes and military personnel, in whom the supplement showed a small positive effect.
Regarding dosage, the daily requirement for an adult in most countries is approximately 45 milligrams, which can easily be obtained from half an orange or a few pieces of broccoli. Long-term intake of more than 1,000 milligrams of vitamin C per day increases the risk of side effects such as: gastrointestinal issues (diarrhea, nausea), kidney stone formation, and excessive iron absorption (which is particularly dangerous for individuals with undiagnosed hemochromatosis). Additionally, high doses may interfere with chemotherapy and cholesterol-lowering medications (statins).
Consequently, doctors advise avoiding self-prescribed supplements and consulting a specialist regarding dosages, especially given that severe vitamin C deficiency affects a very small portion of the population (less than 4%) in the developed world.
