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 .
Mega-dose vitamin C in treatment of the common cold: a randomised controlled trial.
OBJECTIVE To determine the effect of large doses of vitamin C in the treatment of the common cold . STUDY DESIGN Double-blind , r and omised clinical trial with four intervention arms : vitamin C at daily doses of 0.03 g ( " placebo " ) , 1 g , 3 g , or 3 g with additives ( " Bio-C " ) taken at onset of a cold and for the following two days . PARTICIPANTS AND SETTING 400 healthy volunteers were recruited from staff and students of the Australian National University , Canberra , ACT , between May 1998 and November 1999 . The trial continued for 18 months . INTERVENTIONS Participants were instructed to commence medication when they had experienced early symptoms of a cold for four hours , and to record daily their symptoms , severity , doctor visits and use of other medications . MAIN OUTCOME MEASURES Duration of symptoms and cold episodes ; cumulative symptom severity scores after 7 , 14 and 28 days ; doctor visits ; and whether participants guessed which medication they were taking . RESULTS 149 participants returned records for 184 cold episodes . No significant differences were observed in any measure of cold duration or severity between the four medication groups . Although differences were not significant , the placebo group had the shortest duration of nasal , systemic and overall symptoms , and the lowest mean severity score at 14 days , and the second lowest at 7 and 28 days . CONCLUSIONS Doses of vitamin C in excess of 1 g daily taken shortly after onset of a cold did not reduce the duration or severity of cold symptoms in healthy adult volunteers when compared with a vitamin C dose less than the minimum recommended daily intake
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 .