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 ?
Vitamin C and the common cold: a second MZ Cotwin control study.
Self-reported cold data have been analyzed for 95 pairs of identical twins aged 14 - 64 who took part in a double-blind trial of vitamin C tablets .  One member of each twin pair took a tablet containing 1 g vitamin C and the other took a well-matched placebo each day for 100 days . In the total sample there was no effect of vitamin C in preventing colds . However , subdivision of the data showed a significant preventive effect of the placebo in the 51 pairs living together and an equal and opposite preventive effect of the vitamin C in the 44 pairs living apart . The placebo effect in the pairs living together may be attributed to the large proportion who wrongly perceived which treatment they were taking . The reduction of colds in the vitamin C group of the pairs living apart was about 20 % . There were significant correlations between cold symptoms reported and the personality trait of neuroticism . No side effects of substantive changes in serum biochemistry could be attributed to the vitamin C dose
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 ?