No wonder many people take huge doses. Yet several studies suggest the vitamin may have a Jekyll-and-Hyde character: At 500 milligrams daily – a dose higher than the RDA but lower than the amount frequently taken to beat back colds – it may cause the kind of genetic damage that can lead to cancer. Until all the facts are in, it’s wise to rely on your diet for C; if you want to supplement, take no more than 500 mg daily.

Beyond that, people with a tendency to develop kidney stones can increase their risk; too much C can also promote diarrhea. In fact studies show that in certain instances where people have complained of food poisoning, too much vitamin C was the culprits. Clearly people are just not aware how potent these vitamin supplements are.

Also, taking extra vitamin C does not seem to be as useful to protecting smokers’ lungs as it was made out to be.