Vitamin C can have significant benefits for our immune system and with few side effects for too high a dose. It won't necessarily stop you catching a cold but many research studies show it reduces the length and severity of these. Naturopaths often recommend doses of 3000mg to 10,000mg per day.
Very high doses of Vitamin C have been found to help battle cancer. Whilst conventional medicine (and a pharmaceutical industry with a billion pound turnover from cancer drugs) scoff at this, the research and findings were made by the eminent scientist Linus Pauling, one of only two people to ever win a Nobel Prize in two separate areas (the other was Marie Curie). I'm taking very high doses to boost my system at the moment (up to 15,000mg)
GG x