The fact that I and people I know can take 10 times this amount with no stomach pain or diarrhoea would rather cast doubt on its validity.
I don't see why it would cast any doubt at all. I think it should simply add to the need for skepticism regarding claims that vitamin C (or any medication, vitamin, etc) has no adverse side effects. Some medications can have severe or deadly side effects and every person is different.
Though I do have a negative attitude to the pharmaceutical industry in general I believe that the rise of self medicating via herbs and vitamins is a very risky venture. Without studies to understand the potential risks to these
treatments I tend to see them as Russian roulette.
Have you heard about
Hydrogen Peroxide Therapy? Two of my uncles decided to do this, both swore that it had positive results and they felt much healthier as a result. One of them had no reaction, the other simply by building a deck developed arsenic poisoning, nearly died, and will suffer from the effects likely for life. His doctors believe that Hydrogen Peroxide Therapy was a possible contributing factor. (Without questioning him further I cant provide much details beyond this, exactly what ill effects he suffers I cant describe in detail) There can be a variety of reasons why he was more susceptible to arsenic than others, Hydrogen Peroxide Therapy may have nothing to do with it, but without real studies into the lasting effects of such things it becomes impossible to know for sure.
Though this story is also anecdotal it was convincing enough for me as a non-medical professional to be extremely skeptical when deciding to self medicate. I am much more comfortable knowing that real studies have been conducted by scientists when I am recommended a medication from my doctor.
Sorry for interrupting such an interesting discussion. I just wanted to add my two cents in support for the skeptics.