Nobel laureate Linus Pauling, Ph.D., in his last interview months before his death (April 1994), continued to advocate high doses (megadoses) of vitamin C to cure and prevent colds, prolong the lives of terminal cancer patients and prevent other ailments. The basic premise of his avocation of vitamin C in these doses was that because man was one of the few animals that do not produce its own vitamin C, it is somehow a design flaw in our genetic make-up. He calculated that an average adult should need about 10-12 grams of vitamin C daily to prevent a wide range of ailments.
One myth about vitamin C is that it is an antioxidant, but that is not completely true. Vitamin C is a redox agent, meaning that it acts as an antioxidant in some cases, and an oxidant in others. Antioxidants are important because they inhibit chemical reactions with oxygen or highly reactive free radicals. These reactions (oxidation reactions), cause damage to cells. Vitamin C only acts as an antioxidant in some circumstances.
Recent research has indicated that the intake of antioxidants can prevent or counteract cell damage due to aging and exposure to free radicals. However, studies have yet to prove that vitamin C's effectiveness at the cell level translates to the prevention of or cure for chronic diseases.
Vitamin C has not been shown to prevent the common cold. High doses of vitamin C at the beginning of a cold has only been shown in some cases to reduce the severity of the symptoms to a modest degree, due to a mild antihistaminic effect. Similar high doses of vitamin C used for the treatment of cancer patients have not been found to be beneficial. For example, research done at the Mayo clinic in a double blind trial (neither the doctors or the patients knew who was given the high doses of vitamin C) revealed that those who received the vitamin C in the high doses actually did worse than those who got a placebo.
Some people believe that because vitamin C is water-soluble, it is safe to take in high doses. While it is best to not exceed the recommended upper intake level of 2,000 mg a day, the most serious possible consequence of an intake above this dosage is diarrhea.
Vitamin C is an important part of a healthy diet. It is not a miracle drug, and may cause harm if taken in extreme excess. A well-balanced, varied diet will ensure that you receive more than enough vitamin C to prevent scurvy and other potential health problems.
For lots more information on Vitamin C and other vitamins, check out the links below.