Vitamin C for Preventing and Treating the Common  Cold  
Harri Hemilä, Elizabeth Chalker, and Cochrane Acute Respiratory Infections Group Despite several controlled experiments, the usefulness of oral ascorbic acid (vitamin C)  in the prevention and treatment of colds remains contentious. There have also been several  attempts to synthesize and/or summarize the outcomes of these experiments, as well as debate  about what these summaries reveal. There were thirty trials in total. The quality of the trials  included in the study was mixed. Vitamin C at high dosages, up to one gram per day, showed no  consistent effect on the occurrence of the common cold during multiple winter months. There  was a consistently favorable but typically moderate therapeutic impact on the duration of cold  symptoms in both preventative and therapeutic studies. There was no clear evidence of the  relative advantages of various vitamin C regimens or dosages. Colds do not appear to be  prevented by taking high amounts of vitamin C on a regular basis for a long time. Vitamin C  ingestion at quite high doses appears to provide a minor benefit in reducing the duration of cold  symptoms. More research on the link between dose and therapeutic benefit is required.