Benefits of Green Tea and Cancer Prevention
By Robert Rogers
Tea and Cancer Prevention
Tea drinking is an ancient tradition dating back 5,000
years in China and India. Long regarded in those cultures as an aid
to good health, researchers now are studying tea for possible use
in the prevention and treatment of a variety of cancers. Investigators
are especially interested in the antioxidants-called catechins-found
in tea.
1. What are antioxidants?
The human body constantly produces unstable molecules
called oxidants, also commonly referred to as free radicals. To become
stable, oxidants steal electrons from other molecules and, in the
process, damage cell proteins and genetic material. This damage may
leave the cell vulnerable to cancer.
Antioxidants are substances that allow the human body
to scavenge and seize oxidants. Like other antioxidants, the catechins
found in tea selectively inhibit specific enzyme activities that lead
to cancer. They may also target and repair DNA aberrations caused
by oxidants (1).
2. What is the level of antioxidants found in tea?
All varieties of tea come from the leaves of a single
evergreen plant, Camellia sinensis. All tea leaves are picked, rolled,
dried, and heated. With the additional process of allowing the leaves
to ferment and oxidize, black tea is produced. Possibly because it
is less processed, green tea contains higher levels of antioxidants
than black tea.
Although tea is consumed in a variety of ways and
varies in its chemical makeup, one study showed steeping either green
or black tea for about five minutes released over 80 percent of its
catechins. Instant iced tea, on the other hand, contains negligible
amounts of catechins (1).
3. What are the laboratory findings?
In the laboratory, studies have shown tea catechins
act as powerful inhibitors of cancer growth in several ways: They
scavenge oxidants before cell injuries occur, reduce the incidence
and size of chemically induced tumors, and inhibit the growth of tumor
cells.
In studies of liver, skin and stomach cancer, chemically
induced tumors were shown to decrease in size in mice that were fed
green and black tea (1, 2).
4. What are the results of human studies?
Although tea has long been identified as an antioxidant
in the laboratory, study results involving humans have been contradictory.
Some epidemiological studies comparing tea drinkers to non-tea drinkers
support the claim that drinking tea prevents cancer; others do not.
Dietary, environmental, and population differences may account for
these inconsistencies.
Two studies in China, where green tea is a mainstay
of the diet, resulted in promising findings. One study involving over
18,000 men found tea drinkers were about half as likely to develop
stomach or esophageal cancer as men who drank little tea, even after
adjusting for smoking and other health and diet factors (3).
A second study at the Beijing Dental Hospital found
consuming 3 grams of tea a day, or about 2 cups, along with the application
of a tea extract reduced the size and proliferation of leukoplakia,
a precancerous oral plaque (1).
5. Is NCI evaluating tea?
National Cancer Institute (NCI) researchers are also
investigating the therapeutic use of green tea. One recently completed
but unpublished NCI trial studied the antitumor effect of green tea
among prostate cancer patients. The 42 patients drank 6 grams of green
tea, or about 4 cups, daily for four months.
However, only one patient experienced a short-lived
improvement, and nearly 70 percent of the group experienced unpleasant
side effects such as nausea and diarrhea. The study concluded drinking
green tea has limited antitumor benefit for prostate cancer patients
(5).
Other ongoing NCI studies are testing green tea as
a preventive agent against skin cancer. For example, one is investigating
the protective effects of a pill form of green tea against sun-induced
skin damage while another explores the topical application of green
tea in shrinking precancerous skin changes.
Robert is a writer in the Washington DC area and
specializes in health and fitness. Visit pcshealth.com
for more articles and research on green tea.
Green
tea is a potent cancer-fighter. It is a known fact that people who
drink green tea are less likely to develop cancer. A new study indicates
green tea's ability to fight cancer is even more potent and varied
than scientists have suspected.
Researchers say they've discovered chemicals in green
tea that shut down one of the key molecules that tobacco relies upon
to cause cancer. The finding by scientists at the University of Rochester's
Environmental Health Science Center appears in the journal Chemical
Research in Toxicology, published by the American Chemical Society.
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Evidence of green tea's health-promoting
benefits came from the Japanese culture. The Japanese have the lowest
level of heart disease and highest longevity rate of all industrialized
nations. Although many aspects contribute to the Japanese low-disease
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- Top antioxidant in Asia.
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