I also want to add that while vitamin C is considered an antioxidant it does not act the same as other antioxidants such as vitamin E and NAC, which have actually been shown to accelerate tumor growth. Vitamin E and NAC can sequester reactive oxygen species (which activates cancer cell death) and prevents cancer cells from dying. Vitamin C does not act the same way. This is why it is VERY important to understand mechanisms and not make generalizations. Vitamin C is in constant homeostasis between oxidized and reduced forms and this depends on many factors including dose. When administered intravenously, the vitamin C dose is so high that it forms the oxidized form and this does a couple of important things that can kill cancer cells. First, it causes oxidative stress in cancer cells (a well known mechanism to activate cell death of a cancer cell). Second, it inhibits the glycolysis pathway, thus starving cancer cells of glucose.