To reduce your risk of cancer, choose a balanced diet with a variety of foods rather than taking supplements. The expert report found strong evidence that high-dose supplements of some nutrients can affect the risk of different cancers. The panel judged that in general, the best source of nourishment is food and drink, not dietary supplements. Nutrient-rich whole foods contain substances that are necessary for good health–like fiber, vitamins, minerals and phytochemicals.
Some studies have shown that supplements can upset the balance of nutrients in the body. More research needs to be done, but this is one way that they might affect our risk of cancer. – American Institute for Cancer Research (http://www.aicr.org/)