Actually, while I'll agree with you that the latest research doesn't support any prophylactic effect from taking vitamin C for colds and the like, I'm going to disagree with your conclusion.
Vitamin C does have a number of effects that make it worth taking during a cold or flu. Biochemically, vitamin C has a number of roles, such as deactivating histamine, which is one of the causes of feeling sick when you're sick, and it plays a major role in free radical clean up.
When you're sick, your immunocytes are attacking the invading pathogen with such wonderful enzymes as myeloperoxidase, which take hydrogen peroxide (produced in the oxidative burst) and turn it into HOCl (bleach) in order to kill the pathogen. This process spews reactive oxygen species (free radicals). When the ROSs interact with your cells, they cause damage, which leads to cytokine release and mast cell degranulation. Mast cells are the primary histamine releasers. So, not only is Vitamin C involved in the cleaning up of free radicals (in that vitamin C will quench the free radical, by itself becoming a free radical, albeit a safer and more stable one), but it also deactivates histamine.
Additionally, if you'd care to do the research, most of the studies showing megavitamin therapy (in the case of vitamin C) to be ineffective have either been performed by those with an interest in showing that it's ineffective (i.e. the drug companies), or had indeterminate conclusions.
Much more research needs to be done on the subject, but since the only problem with (oral, at least) vitamin C therapy seems to be osmotic diarrhea at more than 2g/day intake, in my opinion, there is no reason not use it for this purpose.
IAAMedStudent
