@FaheemMitha Vitamin C -> shorter colds would be an extremely straightforward effect. Nothing like that has been found. Something like Vitamin C + exercise + a specific genotype -> shorter colds would be complex enough to evade the studies we've fielded so far.
@FaheemMitha I mean the scientific community. Stuff like Airborne(tm) has been shown to have no effect on illness, so i'm comfortable declaring Vitamin C useless*
I think Vitamin C works on me at least, and I've heard anecdotal evidence it works on other people. But of course, as you say, there could be multiple factors at play, and probably are.