REVIEW ERS ' CONCLUSIONS 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 .
BACKGROUND The role of oral vitamin C ( ascorbic acid ) in the prevention and treatment of the  common cold  has been a subject of controversy for at least sixty years .
Public interest in the topic continues to be high and vitamin C continues to be widely sold and used as a preventive and therapeutic agent for this common ailment .
OBJECTIVES To discover whether oral vitamin C in doses of 200 mg or more daily , reduces the incidence , duration or severity of the common cold when used either as continuous prophylaxis or after the onset of cold 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
REVIEW ERS ' CONCLUSIONS 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 .
BACKGROUND The role of oral vitamin C ( ascorbic acid ) in the prevention and treatment of the  common cold  has been a subject of controversy for at least sixty years .
Public interest in the topic continues to be high and vitamin C continues to be widely sold and used as a preventive and therapeutic agent for this common ailment .
OBJECTIVES To discover whether oral vitamin C in doses of 200 mg or more daily , reduces the incidence , duration or severity of the common cold when used either as continuous prophylaxis or after the onset of cold symptoms .