Our analysis of the available evidence so far focuses on a single assertion: taking vitamin C at the start of a cold does not shorten the illness or make symptoms less severe. That claim is supported by 39 studies we reviewed, with zero studies refuting it. So the evidence we've seen leans toward vitamin C being ineffective for reducing cold duration when taken after symptoms begin. We want to be clear that this is our current analysis based on the studies we have examined. The numbers are lopsided, but we do not claim this is proven or settled — it is simply what the evidence we've reviewed shows up to this point [1]. Practically, if you feel a cold coming on and take vitamin C right away, our reading of the research suggests you should not expect it to make the cold shorter or less intense. Other strategies like rest, hydration, and over-the-counter symptom relief may be more helpful based on what we've found so far.