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Tea is one of the
most widely consumed beverages in the world, second in
popularity only to water. People in China and India have long
associated drinking tea with good health. Now researchers around
the world are studying the potential health benefits of tea,
particularly as it relates to the prevention and treatment of
various types of cancer. The primary focus of this research is
on a particular substance, called an antioxidant.
What
Are Antioxidants?: During the process of normal
metabolism, our cells are constantly forming harmful substances
called free radicals. These free radicals are hazardous because
they are molecularly unstable and must steal electrons from
other molecules in the cell in order to become stable.
Unfortunately, this electron theft can damage both proteins and
DNA, leaving the cell vulnerable to cancer.
To guard against
the harm caused by unchecked free radicals, our cells have
developed ways to absorb some of them before they have a chance
to wreak their full havoc. In addition, our diet contains
substances called antioxidants, which do essentially the same
thing. Fruits, vegetables, and certain teas are particularly
rich in these antioxidants. Because of their protective effect,
some researchers believe that high consumption of antioxidants
can reduce the risk of certain cancers.
Which
Antioxidants are Found in Tea?: Catechins are the
type of antioxidants found in tea. All black or green teas come
from the leaves of a single type of evergreen plant called
Camellia sinesis. When the tea is ready, it is picked, rolled,
dried, and heated. This is green tea. To produce black tea, the
leaves are allowed to ferment and oxidize. This presumably
explains why green tea contains higher levels of antioxidants
than black tea. Research has shown that steeping either green or
black tea for about five minutes releases as much as 80% of its
antioxidants. Instant iced tea, on the other hand, contains
almost none.
What
Does the Research Say?: In the laboratory, teas
rich in catechins have been shown to:
-
Destroy
oxidants before they have the chance to do damage
-
Inhibit the
growth of tumor cells
-
Reduce the
number and size of existing tumors
In studies of
mice with skin, liver, and stomach cancer, for example, tumors
decreased in size when the mice were fed either green or black
tea.
Unfortunately,
studies in humans have shown contradictory results. This may be
due in part to variations in diets, environments, and genetics
that are more difficult to control for in human populations.
In China, where
green tea is a mainstay of the diet, two studies showed
promising results. One study of 18,000 men found that tea
drinkers were half as likely to develop stomach or esophageal
cancer compared with men who did not drink tea. However, another
study conducted in the Netherlands did not support a protective
effect for tea. This study included 58,279 men and 62,573 women
and found no link between drinking black tea and the subsequent
risk of stomach, colorectal, lung, or breast cancers.
One interesting
study, conducted at the University of Arizona College of
Medicine, looked at the effects of tea on skin cancer. The
researchers wanted to know if there was any connection between
tea drinking habits and the odds of developing of squamous cell
cancer of the skin. They found those who preferred their tea
hotter and stronger tended to have lower rates of this type of
cancer compared to the other participants.
The
Bottom Line: The bottom line is that many researchers
believe, but have not yet been able to prove conclusively, that
drinking tea has a protective effect when it comes to certain
kinds of cancer. Nor do they know if these protective effects
are found equally in both green and black tea, or if one type of
tea offers more protective effects than the other.
Controlled,
randomized clinical trials are currently underway at the
National Cancer Institute (NCI) and other institutions around
the world to determine the true effectiveness of tea in
preventing or treating cancer. In the meantime, whether green or
black, if it’s your cup of tea…enjoy!
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