Prostate cancer and green tea

FROM


January 12, 1999

ROCHESTER, Minnesota (MAYO CLINIC) -- Prostate cancer is the most common cancer among U.S. males. It is the second leading cause of cancer death — trailing only lung cancer — in that group.

Researchers have known for years that the incidence of prostate cancer is considerably lower in Asian countries. One possible explanation advanced by scientists is the high consumption of plant foods among Asian populations. Another is the growing number of laboratory studies indicating that green tea — the most popular tea in China, Japan and other Asian countries — has anti-tumor effects.

Black tea is more popular in Western countries. Worldwide, about 80 percent of the tea consumed is black tea. Both teas come from the same plant (Camellia sinensis). Black tea is fermented; green tea is not. Next to water, tea is the most widely consumed beverage in the world.

Green tea contains more polyphenols — chemicals that act as powerful antioxidants and nontoxic, cancer preventive agents — than black tea. It has been speculated that the low lung cancer rate in Japan — despite the high rate of smoking — is due to green tea consumption.

Mayo Clinic researchers have identified a plant substance in green tea that is a potent killer of prostate cancer cells. Charles Y-F. Young, Ph.D., and colleagues tested four common components of green tea on cell cultures of three different lines of prostate cancer. One of the tea components, called EGCG, was found to be most potent in inhibiting the growth of prostate cancer cells. Young says the chemical structure of EGCG is similar to substances found in red wine and vegetables.

The Mayo Clinic study, published in Aug. 14, 1998, issue of the journal Cancer Letters, found that green tea not only inhibited cell growth, it also produced fragmented nuclei and other signs of apoptosis, or programmed cell death.

The researchers, however, caution that tea's composition is very complex and that other compounds might contribute to the cancer-fighting properties of green tea. Mayo researchers now are testing whether EGCG can reduce the rate of cancer in a special strain of mice that develops prostate cancer. Young says that human trials could follow if the results are promising.

The Mayo study was supported by grants from the National Institutes of Health and the National Cancer Institute. Oasis spoke with Young, a urology researcher, about the findings.

Oasis: Are you also looking into green tea's effect on other types of cancer?

Young: We're just beginning to study the effects of green tea polyphenols on breast cancer cells. We don't have plans to expand the study to other cancers in the near future.

Oasis: Can you put your findings into some context? For example, should a man with early prostate cancer consider green tea as a possible treatment alternative?

Young: The history of green tea suggests more benefits to our health than harm. However, at this time it's impossible to say whether green tea will ever be a possible cure for even early-stage prostate cancer. Much more research and clinical trials still need to be done.

One of our purposes is to understand the molecular mechanisms by which green tea compounds exert anti-prostate cancer effects. By doing so, we hope that we can learn from nature how to design better ways to prevent or combat prostate cancer. Another preliminary study of ours indicates that green tea may have a role in prostate cancer prevention. The next step is to extend our study to specially bred mice to examine the effectiveness of green tea on the prevention of prostate cancer.

Oasis: How does EGCG kill prostate cancer cells? Do other foods or drinks contain EGCG or similar substances?

Young: Although the actual molecular mechanism by which EGCG kills prostate cancer cells is not completely clear, our data indicate that EGCG, at low concentrations, may inhibit cell growth. At high concentrations, it killed cells by inducing apoptosis, or programmed cell death.

Tea polyphenols (also known as tea catechins) belong to the plant phenol family of chemicals. Unfermented tea leaves may contain up to 30 percent dry weight of tea polyphenols, mostly EGCG. Another example of plant phenols is resveratrol, found in grapes used for making red wine. In plants, phenols mainly ward off microbial or viral infections as well as acting as antioxidants to scavenge oxygen radicals. They also are the building blocks for plant cell structures.

In people, intake of these compounds may be associated with reduced risks of coronary heart disease and certain cancers. It was believed that the anti-cancer effects of these plant phenols were largely due to their antioxidant activities. However, recent studies have demonstrated that these compounds have broader biological effects in animal and human systems. Some of these effects include cell growth inhibition, apoptosis, and the activation of estrogen receptors.

Oasis: Is there any hard science behind the assertion that the incidence of prostate cancer may be lower in Asia because of high green tea consumption?

Young: I'm afraid not. Although many studies indicate that tea consumption may reduce the risks of certain cancers, there is no clear evidence that drinking tea reduces prostate cancer. This may be because there are very few studies regarding the effects of tea on prostate cancer.

Oasis: What about black tea, oolong or other types of tea? Do they contain EGCG?

Young: EGCG exists in fresh tea leaves as well as in green tea. Green tea is the leaf product that is quickly heated and dried right after harvest. The original forms of EGCG and other tea catechins are preserved by this method. However, black tea and other teas may have been through different degrees of processing, resulting in much lower amounts of tea catechins. In general, green tea polyphenols are more potent in anticancer activities than black tea polyphenols.

Copyright © 1998 Tealand. All rights reserved.
Revised: August 04, 2009.