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 ?
Common cold and vitamin C.
Abstract The effect of daily administration of placebo or 200 or 500 mg . tablets of vitamin C on symptom association and on the incidence , duration , severity , and total intensity of the symptoms  in the common cold has been studied . The metabolism of ascorbic acid during the common cold , and after disappearance of all the symptoms , has been investigated by examining the plasma and leucocyte ascorbic-acid concentrations after a loading dose of 500 mg . vitamin C. Cold symptoms tend to dissociate into toxic and catarrhal complexes , the complexity and frequency of which differ between boys and girls .  Vitamin C reduces symptom association and alters the frequency of toxic and catarrhal complexes . It significantly reduces the severity and total intensity of colds in girls , but does not benefit cold symptoms in boys at a daily dose of 500 mg . During colds , especially of the catarrhal variety , ascorbic acid is transferred out of the leucocytes into the plasma , where it is rapidly metabolised in both sexes , but this effect is more pronounced in females . There is a significant positive correlation between metabolic utilisation of ascorbic acid during colds and intensity of cold symptoms
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 ?