Soy-Tea Combo May Thwart Prostate Cancer

Taken together, they inhibited tumor growth in mice

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HealthDay Reporter

WEDNESDAY, Feb. 5, 2003 (HealthDayNews) -- The same two foods that many scientists believe reduce the risk of breast cancer in women may also protect men from prostate cancer.

That's the conclusion of a new Harvard University study that looked at the power of tea and soy to inhibit the growth of prostate tumors in mice.

Unlike other studies that examined the food's individual effects on tumor growth, the new research focused on the power that came from the combined effect of tea and soy together.

"I think the most important finding is that consumption of both soy and tea has a synergistic effect," says study author Jin-Rong Zhou, adding that each appears to reinforce the power of the other to fight cancer.

The study appears in the February issue of The Journal of Nutrition.

Zhou says he got the idea to test the soy-tea combination when statistical data showed that China had one of the lowest prostate cancer risk profiles in the world. Sensing that diet may play a key role, he dissected Chinese food habits and looked at what the men were eating most.

While a number of foods made the list, Zhou says tea and soy jumped out, mostly because previous studies showed they may possess anti-cancer properties.

"By combining the facts that soy and tea are more commonly consumed [in China] and their bioactive components are more potent than other dietary components, we proposed that they are effective dietary components, especially in combination, for prostate cancer prevention," Zhou says.

Zhou and his colleagues put their theory to the test on 16 mice, each genetically engineered to grow tumors in the prostate region. All the mice ate a diet of protein, carbohydrates, vitamins and minerals, while some were also fed daily doses of soy compound in varying amounts. Infusions of both black and green tea were given to all the mice to drink.

The amount of soy consumed by the mice would be equivalent to about 250 milligrams per day for a human, while the tea dose was equivalent to about 6 to 8 cups a day, Zhou says.

At the end of the study, the mice were examined for not only the presence of prostate tumors, but also the size of the tumors, their rate of growth and how much the disease had spread. These figures were then analyzed in regard to soy and tea consumption.

What the researchers found: Individually, the soy complex, and the black and green tea reduced the rate at which tumors developed. When tumors did grow, they were smaller when either tea or soy was consumed.

However, when taken together, the tea-soy combination was even more powerful, not only at inhibiting tumor growth, but also at reducing the weight of any tumors that did develop, as well as controlling the spread of cancer to nearby lymph nodes. The soy and green tea combination also reduced hormone concentrations linked to prostate cancer.

Ultimately, both tea-soy combinations inhibited angiogenesis, a process in which tumors grow blood vessels to stay alive.

The bottom line: Alone and especially together, tea and soy exhibited powerful anti-prostate cancer effects, the study says.

For nutritionist Jyni Holland, the research holds promise, but she doesn't think men should flood their diet with tea or soy just yet.

"Keep in mind that it was a mouse study, and many promising animal results never translate to human success," says Holland, a clinical nutritionist at New York University Medical Center.

At the same time, she says that since both tea and soy have been shown in other studies to yield many important health benefits, adding them to your diet in moderation could have positive results.

"I wouldn't run out and buy soy or green tea supplements. But if you want to include these foods in your diet, then you may be well ahead of the game if and when this research does prove true in humans," Holland says.

More information

To learn more about the heath benefits of tea, visit Kansas State University. For more information on prostate cancer, check with The National Prostate Cancer Coalition.

SOURCES: Jin-Rong Zhou, Ph.D., assistant professor, surgery, Harvard Medical School, and director, Nutrition/Metabolism Laboratory, Beth Israel Deaconess Medical Center, both in Boston; Jyni Holland, M.S., R.D., clinical nutritionist, New York University Medical Center, New York City; February 2003 The Journal of Nutrition

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