The second mechanism of action is actually a pro-oxidant effect. This is the little know but powerful anti-cancer mechanism of vitamin C. Doses above 15g have been shown to have a “pro-oxidant” effect by generating hydrogen peroxide, which selectively destroys cancer cells. These high doses are only possible through intravenous therapy since oral supplements are limited by absorption in the digestive tract. High doses of vitamin C are delivered to the areas surrounding the tumor because the vitamin C molecule looks similar to a sugar molecule and cancer cells have an increased demand for sugar to fuel their unregulated growth. When in the area surrounding the cells, the vitamin C molecule reacts with transition metals such as iron or copper and forms a hydrogen peroxide molecule that damages the cancer cell. The picture below shows the formation of the hydrogen peroxide molecule outside the cancer cell. One proposed idea on why cancer cell are particularly vulnerable to hydrogen peroxide is that they don’t have the enzyme catalase to break it down.
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Chen Q, Espey MG, Sun AY, Pooput C, Kirk KL, Krishna MC, Khosh DB, Drisko J, Levine M. Pharmacologic doses of ascorbate act as a prooxidant and decrease growth of aggressive tumor xenografts in mice. Proc Natl Acad Sci U S A. 2008 Aug
Chen et al. Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo. Proc Natl Acad Sci U S A. 2007 May 22;104(21):8749-54.