Overall, this is further evidence that eating natural, real foods (in moderation) and avoiding supplements is best for health. Don't want to feed any cancers. From Science Daily:
For decades, health-conscious people around the globe have taken antioxidant supplements and eaten foods rich in antioxidants, figuring this was one of the paths to good health and a long life.Yet clinical trials of antioxidant supplements have repeatedly dashed the hopes of consumers who take them hoping to reduce their cancer risk. Virtually all such trials have failed to show any protective effect against cancer. In fact, in several trials antioxidant supplementation has been linked with increased rates of certain cancers. In one trial, smokers taking extra beta carotene had higher, not lower, rates of lung cancer.
Two cancer researchers have proposed why antioxidant supplements might not be working to reduce cancer development, and why they may actually do more harm than good. Their insights are based on recent advances in the understanding of the system in our cells that establishes a natural balance between oxidizing and anti-oxidizing compounds. These compounds are involved in so-called redox (reduction and oxidation) reactions essential to cellular chemistry.
Drs. Tuveson and Chandel propose that taking antioxidant pills or eating vast quantities of foods rich in antioxidants may be failing to show a beneficial effect against cancer because they do not act at the critical site in cells where tumor-promoting ROS (reactive oxygen species) are produced -- at cellular energy factories called mitochondria. Rather, supplements and dietary antioxidants tend to accumulate at scattered distant sites in the cell, "leaving tumor-promoting ROS relatively unperturbed," the researchers say.
Quantities of both ROS and natural antioxidants are higher in cancer cells -- the paradoxically higher levels of antioxidants being a natural defense by cancer cells to keep their higher levels of oxidants in check, so growth can continue. In fact, say Tuveson and Chandel, therapies that raise the levels of oxidants in cells may be beneficial, whereas those that act as antioxidants may further stimulate the cancer cells. Interestingly, radiation therapy kills cancer cells by dramatically raising levels of oxidants. The same is true of chemotherapeutic drugs -- they kill tumor cells via oxidation.