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updated 1/21/2005 2:30:01 PM ET 2005-01-21T19:30:01

New research suggests that phytochemicals in green tea may help prevent the spread of prostate cancer. Since earlier research suggests that the same natural plant substances might also help prevent the development of prostate cancer, scientists say that more studies are needed on green tea’s ability to fight this common cancer.

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The best way to reduce your risk of prostate cancer, however, still lies in eating a mostly plant-based diet.

In the new green-tea study, researchers observed that phytochemicals called polyphenols attack growth factors and proteins, interrupting processes that increase the size of tumors, thus preventing them from spreading to other parts of the body.

Further study of green tea may help develop a treatment to prevent the dormant, nonthreatening type of prostate cancer many men have late in life from becoming aggressive and fatal.

Studies presented at the most recent American Institute for Cancer Research (AICR) conference on diet and cancer also show that green tea in mice with an aggressive form of cancer can decrease the spread or metastasis of prostate cancer to liver, bone and other sites.

Supplements may help
About six cups of green tea per day would contain the equivalent amount of polyphenols for humans to alter the balance of bodily processes and substances that will help block the spread of cancer.

Furthermore, data presented at the AICR conference show that the phytochemicals in green tea could inhibit the early stages of prostate cancer development.

For example, the phytochemicals seem to increase the number of enzymes that convert carcinogens to inactive, harmless forms. For now, however, many questions remain about the amount and frequency of green tea necessary to halt the formation of prostate cancer. Although black tea has shown similar benefits to green tea, it appears to have lower levels of the beneficial substances.

In any case, it would be a mistake to rely on tea alone for prevention. Studies suggest that there are a variety of nutritional influences on prostate cancer risk. Vitamin E may offer some protection.

In several important studies, the antioxidant mineral selenium also seems protective. Almost all Americans get adequate amounts of selenium, but these scientific studies used supplements, so the study participants reached higher intake levels.

It is unclear, however, whether men can protect themselves more from prostate cancer by taking supplements, including multivitamins, with selenium and eating more selenium-rich seafood, grains and vegetables. If a person’s total selenium intake exceeds 400 mcg per day, nerve damage and other side effects can occur.

Don't forget veggies
According to more research presented at the AICR conference, two or more servings per week of raw or cooked tomatoes lower the risk of prostate cancer about 25 percent. The antioxidant phytochemical called lycopene is often credited for the risk reduction, but other substances in tomatoes may play a role.

Another protective phytochemical in cruciferous vegetables like broccoli was mentioned at the AICR conference. This phytochemical, indole-3-carbinol, seems to increase the body’s ability to block carcinogens and halt the development of prostate cancer cells. Phytochemicals in soy foods are also considered protective.

If men want to lower their risk of prostate cancer, they should not consider drinking green tea as a replacement for a healthy, plant-based diet.

However, it is reasonable to replace less healthy drinks with tea. Although black tea has health benefits, green tea’s higher levels of phytochemicals called catechins may make it more potent.

When combined with a mostly plant-based diet, the phytochemicals from tea could have an even greater effect as all the plant substances interact together to safeguard your health.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

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