Vitamin C in doses as high as one gram daily for several winter months , had no consistent beneficial effect on incidence of the common cold .
For both preventive and therapeutic trials , there was a consistently beneficial but generally modest therapeutic effect on duration of cold symptoms .
There was no clear indication of the relative benefits of different regimes or vitamin C doses .
However in trials that tested vitamin C after cold symptoms occurred , there was some evidence that a large dose produced greater benefits than lower doses .
REVIEW ER 'S CONCLUSIONS Long term daily supplementation with vitamin C in large doses daily does not appear to prevent colds .
BACKGROUND The role of oral ascorbic acid ( vitamin C ) in the prevention and treatment of colds remains controversial despite many controlled trials .
There have also been a number of efforts to synthesize and /or overview the results of these trials , and controversy over what these overviews tell us .
OBJECTIVES The objective of this review was to answer the following two questions : ( 1 ) Does regular high dosage supplementation with vitamin C reduce the incidence of colds ? (
2 ) Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect ?
The effect on winter illness of large doses of vitamin C.
Between December 1972 and February 1973 , 2349 volunteers participated in a double-blind trial to assess the effect of large doses of vitamin C on the  incidence and severity of winter illness .  In addition , records were kept but no tablets taken during March . Subjects were r and omly allocated to eight treatment regimens : three prophylactic-only ( daily dose 0.25 , 1 or 2 g ) , two therapeutic-only ( 4 or 8 g on the first day of illness ) , one combination ( 1 g daily and 4 g on the first day of illness ) , and two all-placebo . None of the groups receiving vitamin C showed a difference in sickness experience that was statistically significant from that of the placebo groups , but the results obtained were compatible with an effect of small magnitude from both the prophylactic and therapeutic regimens , and an effect of somewhat greater magnitude from the combination regimen . The combination regimen was associated more with a reduction in severity than frequency of illness , although the extra dosage was limited to the first day of illness . In spite of the eightfold range in daily dose , the three prophylactic-only regimens showed no evidence of a dose-related effect , but the 8 g therapeutic dose was associated with less illness than the 4 g therapeutic dose . There was no evidence of side effects from the 1 and 2 g prophylactic doses of vitamin C , and no evidence of a rebound increase in illness during the month following withdrawal of the daily vitamin supplements . On the basis of this and other studies it is suggested that the optimum daily dose of vitamin C is less than 250 mg , except possibly at the time of acute illness , when a larger daily intake may be beneficial
Vitamin C in doses as high as one gram daily for several winter months , had no consistent beneficial effect on incidence of the common cold .
For both preventive and therapeutic trials , there was a consistently beneficial but generally modest therapeutic effect on duration of cold symptoms .
There was no clear indication of the relative benefits of different regimes or vitamin C doses .
However in trials that tested vitamin C after cold symptoms occurred , there was some evidence that a large dose produced greater benefits than lower doses .
REVIEW ER 'S CONCLUSIONS Long term daily supplementation with vitamin C in large doses daily does not appear to prevent colds .
BACKGROUND The role of oral ascorbic acid ( vitamin C ) in the prevention and treatment of colds remains controversial despite many controlled trials .
There have also been a number of efforts to synthesize and /or overview the results of these trials , and controversy over what these overviews tell us .
OBJECTIVES The objective of this review was to answer the following two questions : ( 1 ) Does regular high dosage supplementation with vitamin C reduce the incidence of colds ? (
2 ) Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect ?