Vitamin C is a nutrient found in food and dietary supplements. It is an antioxidant and also plays a key role in making collagen. High-dose Vitamin C may be given by intravenous (IV) infusion (through a vein into the bloodstream) or orally (taken by mouth). When taken by intravenous infusion, vitamin C can reach much higher levels in the blood than when the same amount is taken by mouth. High-dose vitamin C has been studied as a treatment for patients with cancer since the 1970s. Laboratory studies have shown that high doses of vitamin C may slow the growth and spread of prostate, pancreatic, liver, colon, and other types of cancer cells.