Just 3 days ago, we found evidence that high dose vitamin C increases one's risk for developing kidney stones .  Ironically, a few days earlier, a review article was published in Cochrane Library in which the authors noted that vitamin C appears helpful in decreasing duration of the common cold in athletic individuals, although it made no difference in terms of incidence.  Obviously dose is as important, since too much can lead to kidney stones, while not enough results in scurvy.  You be the judge!