Tea
Time for Cancer by: Michael Guthrie, R.
Ph. It seems a lot more people are drinking tea these
days, especially green tea. Recent research has found that green tea
contains some very powerful antioxidants. It appears that the
workhorses in green tea are a group of compounds known as
polyphenols. Green tea is manufactured from fresh, unfermented
tealeaves. This process leaves the catechins, potent antioxidants,
intact. The most well researched catechin is epigallocatechin
gallate.
The interest in green tea really took off when a
number of studies were published demonstrating that populations that
consumed green tea had significantly lower incidences of many kinds
of cancer including breast, stomach, liver, pancreatic, lung, skin
and esophogeal. Catechins in green tea appears to prevent cancer by
at least six different mechanisms.
1.They help to neutralize dietary carcinogens such as
nitrosamine and aflatoxin.
2.They interfere with the
binding of cancer-causing agents to cellular DNA, thereby
protecting cells against mutations that can eventually cause
cancer.
3.They protect against free-radical DNA damage
that causes some cancers.
4.They inhibit bacterial-induced
DNA mutations that also can lead to certain cancers.
5.
They work with enzymes and other antioxidants in the intestine,
liver and lungs to prevent the activation of certain carcinogens
before they damage DNA.
6.They protect against the effects
of ionizing radiation and ultraviolet radiation.
One researcher found that mice given green tea were half as
likely to contract cancer than controls when injected with human
non-Hodgkins lymphoma cells. Remarkably the chemotherapeutic drug
cyclophosphamide was not able to reduce the incidence at all!
(Bertolini, 2000).
A couple of recent studies shed light on
the possible mechanism by which green tea exerts its anti-cancer
effects. First, it appears that green tea up-regulates a tumor
suppressor gene called p21. This allows the cell to stop its
uncontrolled growth (Liberto, 2000). Another study indicates that
green tea down-regulates NF Kappa B, a complex that contributes to
uncontrolled cell growth. This allowed cancer cells to commit
programmed cell death (Ahmad, 2000). A recent study done at the
Karolinska Institute in Stockholm found another anti-cancer activity
of green tea. It suppresses angiogenesis, which is the process of
laying down blood vessels by cancer cells (Cao, 1999). Cancer cells
depend on angiogenesis to form tumors. Still, another study found
further anti-cancer activity with green tea. The study, done in
Japan, found that epigallocatechin gallate (one of the main
constituents of green tea), inhibits the secretions of collagenases.
This deprives the cancer cells of a mechanism required for invasion
of adjacent tissues (Sazuka, 1997).
Special benefits in
prostate cancer: Two of the catechins in green tea have been
found to be effective inhibitors of an enzyme that converts
testosterone to dihydrotestosterone. Pharmaceutical products that
have this effect have been shown to be effective in preventing
prostate cancer (Liao, 1995).
One exciting finding about
green tea has to do with its effect on telomerases. Telomeres are
the genetic way of saying "the end" to cell division. In other
words, a cell can only divide so many times. Cancer cells produce
telomerases which destroy the telomeres allowing the cancer to
divide without end (Naasani, et al, 1998). Still another finding
with green tea is its suppression of a growth factor enzyme known as
quinol oxidase (NOX). While expressed in normal cells while
dividing, it is always expressed in cancer cells where it is called
t-NOX. The researchers found that when exposed to the active
ingredients in green tea, the cancer cells were unable to grow after
division, and went into apoptosis (programmed cell death) (Moore,
1998).
