Newsgroup: it.salute.alimentazione
Titolo: Tè verde e prevenzione del cancro?

Forse, almeno per i cinesi... ma altri studi danno risultati contradittori,
a quanto pare. Notare però che nello studio olandese (in cui non è
risultata efficacia) non hanno usato tè verde ma nero.
http://www.cancer.gov/newscenter/pressreleases/tea
 
Key Points
 
    * The antioxidants found in tea--called catechins--may selectively
inhibit the growth of cancer (see Question 1).
    * In laboratory studies using animals, catechins scavenged oxidants
before cell damage occurred, reduced the number and size of tumors, and
inhibited the growth of cancer cells (see Question 3).
    * However, human studies have proven more contradictory, perhaps due to
such factors as variances in diet, environments, and populations (see
Question 4).
    * NCI researchers are investigating the therapeutic and preventive use
of tea catechins against a variety of cancers (see Question 5).
 
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. Despite promising early
research in the laboratory, however, studies involving humans so far have
been inconclusive.
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).
However, a study in the Netherlands did not support these findings. It
investigated the link between black tea consumption and the subsequent risk
of stomach, colorectal, lung, and breast cancers among 58,279 men and
62,573 women ages 55 to 69. The study took into account such factors as
smoking and overall diet. It found no link between tea consumption and
protection against cancer (4). 
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. For more information about NCI-sponsored studies
on green tea, go to 
http://www.cancer.gov/clinical_trials/
===================================

 a quanto pare.
Vero!
Queste cose mi fanno impazzire, perche' uno magari beve te' verde per 10 
anni, e poi ti dicono che si sono sbagliati, che fa male, che anzi nutre le 
cellule cancerose;-)
Comunque a mio avviso e' difficile perche':
* However, human studies have proven more contradictory, perhaps due to
such factors as variances in diet, environments, and populations (see
Question 4).
Dietary,
