But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments
BACKGROUND The role of vitamin C ( ascorbic acid ) in the prevention and treatment of the common cold  has been a subject of controversy for 60 years , but is widely sold and used as both a preventive and therapeutic agent .
OBJECTIVES To discover whether oral doses of 0.2 g or more daily of vitamin C reduces the incidence , duration or severity of the common cold when used either as continuous prophylaxis or after the onset of symptoms .
The effects of ascorbic acid and flavonoids on the occurrence of symptoms normally associated with the common cold.
A controlled study was made of the effects of natural orange juice , synthetic orange juice , and placebo in the prevention of the common cold ; both natural and synthetic orange juices contained 80 mg of ascorbic acid daily . Three-hundred sixty-two healthy normal young adult volunteers , ages 17 to 25 years , were studied for 72 days with 97 % of participants completing the trial . There was a 14 to 21 % reduction in total symptoms due to the common cold in the supplemented groups that was statistically significant ( P less than 0.05 ) . Ascorbic acid supplementation also increased the number of " episode-free " subjects . However , the clinical usefulness of the results does not support prophylactic ascorbic acid supplements in the well-nourished adult . The results in this study with both natural and synthetic orange juice of physiological content of ascorbic acid , are similar to those obtained using a " megadose " of ascorbic acid
But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments
BACKGROUND The role of vitamin C ( ascorbic acid ) in the prevention and treatment of the common cold  has been a subject of controversy for 60 years , but is widely sold and used as both a preventive and therapeutic agent .
OBJECTIVES To discover whether oral doses of 0.2 g or more daily of vitamin C reduces the incidence , duration or severity of the common cold when used either as continuous prophylaxis or after the onset of symptoms .