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New Meds That Heal |
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Green
Tea and Cancer in Humans:
A
Review of the Literature |
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Abstract:
Researchers have investigated green tea as a potential protectant
against cancer. This review focuses on studies of green tea in humans.
Green tea contains polyphenols, chemicals that act as powerful
antioxidants. Epidemiological and human studies have shown varying results.
Thirty-one human studies and four reviews were examined.
Among five studies reporting on colon cancer, three found an inverse
association and one reported a positive association. For rectal
cancer, only one of four studies re- ported an inverse association;
increased risks were seen in two of the studies. An inverse
association is suggested for urinary bladder cancer in two of two
studies. Of JO studies examining the association of green tea and
stomach cancer,
6 suggest an inverse and 3 a positive
association. The most comprehensive of these studies supports an
inverse association of green tea and stomach cancer. Pancreatic
cancer studies hint at an inverse association in two of three studies.
A strong inverse effect was found with
green tea and esophageal cancer. Lung cancer studies have shown an
inverse effect with Okinawan tea, yet tentatively increased risk was
shown in another study. Although human studies have their limitations,
the research has warranted a further look into the effects of green
tea and cancer. |
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Cancer is the second
principal cause of death in the United States. heal1 disease being the
first. Since 1990. approximately 10 million new cancer cases have
been diagnosed in the United States alone. with approximately 4
million cancer deaths. There has been a steadfast rise in the cancer
mortality rate in the United States during the past half-century ( I
). The financial expense of cancer is immense to the individual and
society. Moreover. scientific research suggests that up to one-third
of the 560.000 expected cancer deaths in 1997 were related to
nutrition and dietary factors ( 1 ).
Antioxidants are among the dietary factors that may play a role in
cancer protection. Green tea is an antioxidant-carrying plant that has been arousing
increased attention in cancer research. Unlike previous reviews that
also included |
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black lea and/or
animal studies in their overall analyses, this review uniquely focuses
on human studies and green lea as a possible protectant against
cancer.
Tea is grown in
about 30 countries and, next lo water , is the most widely consumed
beverage in the world. Al- though there is only one plant (Camellia
sinensis), tea is manufactured as black (78%), green (20%), or
oolong (2%) (2.3). Whereas black lea is more popular in Western counties. green tea is primarily consumed in Asian countries. such as
Japan, China. and India. and a few countries in North Africa and the
Middle East (2.4 ). although India also produces and consumes large
amounts of black lea. Leaves meant for green tea are picked by the
same method as those picked for black tea. Black lea is fermented;
green tea is not. Fermentation alters the chemical structure of the
tea leaf, permitting principal flavor attributes to emerge. |
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Green tea contains
polyphenols. chemicals that act as powerful antioxidants. Green tea
contains 35-52% (measured in weight percent of extract of solids)
catechins and flavonols combined. The four major catechins in green
tea are (-)- epicatechin. ( -)-epicatechin-3-gallate,(EGCG)-epigallocathechin,and(-)-epigallocatechin-3-gallate (EGCG). EGCG is the primary
component, accounting for 40% of the total poly- phenolic mixture
(2). One cup of green tea usually contains about 300-400 mg of
polyphenols, which are thought to be nontoxic. Numerous in vitro,
human. and animal studies have identified these antioxidant
polyphenols. in particular EGCG. as cancer-chemopreventive agents
(2,5). Many of the animal and in vitro studies report the
effects of crude green tea extracts, the green tea phenolic fraction,
and its major and most active constituent EGCG (2.6). |
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In
addition to
exerting antioxidant activity on its own, green tea may expand the
activity of antioxidant enzymes. |
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