Vitamin C has been touted as a cancer-fighting agent since the 1970s, and millions of Americans supplement their diets withvitamin C in order to prevent cancer as well as boost immune system function, fight stress, and have more energy.

It has even been suggested by a few on the fringe of the medical community that vitamin C could be a viable cancer treatment if further study could point to how it works. A recent study published in the journal Gut, however, raises questions as to whether or not supplementing an individual’s diet with vitamin C might contribute to cancer.

Vitamin C and fat may interact in the upper stomach to increase formation of nitrosamines, cancer-causing agents formed from nitrates. Nitrates occur naturally within the body, and vitamin C generally combines with nitrates to reduce the formation of nitrosamines, forming nitric oxide instead.

Researchers created an environment to mimic the inside of the stomach. They then replicated the process of vitamin C combining with nitrates in the acidic environment, which promotes the production of nitrosamines, neutralizing the nitrates and creating nitric oxide. Then they introduced 10% fat into the stomach environment, and the vitamin C had an opposite effect. In fact, it increased nitrosamine production anywhere between 8 to 140 times.

Their conclusion was not that vitamin C was dangerous or that it doesn’t in some ways reduce cancer risk. Instead, they concluded that this might be the reason that supplementing an individual’s diet with vitamin C doesn’t appear to greatly reduce cancer risk. It may also point to a hole in the theory that vitamin C could be used to fight cancer.

On the heels of this study comes another study investigating the mechanism of action in vitamin C that makes it a cancer-fighting agent. It was originally believed that vitamin C reduces cancer risk because it and other antioxidants prevented tumor growth by protecting DNA from damage caused by free radicals. Instead, the experiments suggested that vitamin C slows tumor growth by creating inhospitable conditions for the presence of cancer—a conclusion that runs counter to the study suggesting that vitamin C can create cancer-promoting conditions in the stomach.

Clearly, a variety of factors raise cancer risk, and much more research is needed to show a definitive link between vitamin C and the prevention of cancer. One key may be in fat consumption. If vitamin C reduces cancer risk except in the presence of fat, consuming vitamin C as part of a low-fat diet may be one way to reduce the risk.

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