Vitamin C(ascorbic acid) is a common cold remedy, and besides this, some athletes may take large doses believing it may speed recovery.
But does it actually help treat or prevent the common cold, assuming the person isn’t deficient? A great Cochrane Review, conducted at the National Centre for Epidemiology and Population Health, Australian National University, in “Vitamin C for preventing and treating the common cold“:
The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence shows that it could be justified in persons exposed to brief periods of severe physical exercise and/or cold environments. Also, the consistent and statistically significant small benefits on duration and severity for those using regular vitamin C prophylaxis indicates that vitamin C plays some role in respiratory defence mechanisms. The trials in which vitamin C was introduced at the onset of colds as therapy did not show any benefit in doses up to 4 grams daily, but one large trial reported equivocal benefit from an 8 gram therapeutic dose at onset of symptoms.
I won’t be taking vitamin C next time I catch a cold. But how about vitamin C and athletic performance? According to US Olympic Committee, Sport Performance, Olympic Training Center, Chula Vista, CA, in “Effect of vitamin C supplements on physical performance.“:
Vitamin C is an essential component of the diet and may reduce the adverse effects of exercise-induced reactive oxygen species, including muscle damage, immune dysfunction, and fatigue. However, reactive oxygen species may mediate beneficial training adaptations that vitamin C attenuates; indeed, from a total of 12 studies, vitamin C in doses >1 g·d(-1) impaired sport performance substantially in four of four studies, possibly by reducing mitochondrial biogenesis, while a further four studies demonstrated impairments that were not statistically significant. Doses of ∼0.2 g·d(-1) of vitamin C consumed through five or more servings of fruit and vegetables may be sufficient to reduce oxidative stress and provide other health benefits without impairing training adaptations.
It doesn’t look like supplemental vitamin C is a good idea. We only need about 60mg of vitamin C daily to prevent scurvy. Maybe a little more for smokers. This is easily obtainable by eating a diet that includes a lot of fresh fruits and vegetables, citrus fruits in particular. Vitamin C doesn’t seem to be beneficial for either athletes or for preventing/treating the cold, except maybe in some subpopulations living in extreme environments, and maybe it has some modest benefits on respiratory function.