What are the effects of vitamin C on the duration and severity of the common cold?

The common cold causes great morbidity throughout the world and there are no effective therapeutic agents against it. There is a belief that consuming vitamin C during a cold episode would help reduce duration and severity of symptoms. However, there is controversy about this claim.

To answer this question we used Epistemonikos, the largest database of systematic reviews in health, which is maintained by screening multiple information sources, including MEDLINE, EMBASE, Cochrane, among others. We extracted data from the systematic reviews, reanalyzed data of primary studies, conducted a meta-analysis and generated a summary of findings table using the GRADE approach.

We identified four systematic reviews that included eight primary studies overall, of which seven were randomized trials. We concluded vitamin C has minimal or no impact on the duration of common cold or in the number of days at home or out of work.