|
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:
May 11, 2008.
|