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Probing the Benefits of Green Tea
For many centuries, green tea has been consumed and used
medicinally in India, China, Japan and other Asian countries.
Today, millions worldwide not only drink green tea but look for
it in their sunscreen, shampoo and even toothpaste. The website
of one popular nutrition-supplement retailer lists
no fewer than 740 products consisting
of or containing green tea.
But is green tea really a health
elixir, as many believe? And, of particular
interest to many scientists:
Can it fight cancer?
After studying the topic for
16 years, VA scientist Santosh
Katiyar, PhD, MS, is convinced
that green tea, because of its rich
polyphenol content, is among the most potent tumor-inhibitors that nature
provides. In general, he is a feisty proponent
of the Hippocratic maxim "Let food be
thy medicine and medicine be thy food."
In the Oct. 16 online edition of the Journal
of Nutritional Biochemistry, Katiyar
reviewed the latest biomedical findings on
green tea and skin cancer, including those
from his own animal studies at the Birmingham
VA and University of Alabama.
He outlined five mechanisms through
which green tea's most prevalent and active
polyphenol—a robust antioxidant called
epigallocatechin-3-gallate, or EGCG—appears
to protect the skin from ultraviolet
(UV) radiation and prevent tumor formation.
Green tea boosts interleukin-12
One of those pathways was recently
elucidated for the first time in an article
published by Katiyar's group in Cancer
Research. They showed that EGCG prevents
UV-induced cancer in mice through a
DNA-repair mechanism involving interleukin-
12, an important immune-system
chemical.
Experts believe most skin cancer is
caused by solar UV light that penetrates the
skin's top layer and strikes DNA molecules
in the chromosomes, causing harmful mutations.
The process is aided by oxidative
stress and inflammation.
"The polyphenols in green tea have
strong antioxidant and anti-inflammatory
properties," said Katiyar, "but more
importantly, they enhance the production
of interleukin-12, which has a role in DNA
repair. If green tea polyphenols can repair
DNA, then they can prevent skin cancer."
In their experiments, Katiyar's team
exposed two groups of mice to UV radiation
and measured the DNA damage that
occurred. Then, they treated one group with
a topical application of EGCG and left the other group untreated. In the treated mice,
the formation and spreading of tumors
were markedly reduced. Furthermore,
DNA damage was resolved more quickly
in these mice. However, when the same
treatment was given to mice lacking the
gene that codes for interleukin-12 (IL-12
knockout mice) EGCG's protective effect
disappeared.
These and other lab results may be
compelling, but as far as the U.S. Food
and Drug Administration is concerned, the
jury is still out, pending stronger clinical
evidence. A 2005 statement appearing on the FDA website asserts, "Existing
evidence does not support qualified health
claims for green tea consumption and a reduced
risk of [prostate, breast or] any other
type of cancer."
Katiyar suggests that some epidemiologic
and clinical studies on green tea and cancer
may have failed to adequately control
for variables such as climate, race, diet and
frequency of tea consumption, which can
dramatically influence green tea's effects.
Preparing the perfect cup
A native of India who became a U.S. citizen
in the 1990s, Katiyar drinks two cups a
day of green tea. He says people with fairer
skin, who are at higher risk for skin cancer,
may need to drink up to six cups per day to
derive benefit.
For the perfect cup of tea, he advises
that people boil water, remove it from the
heat, and then steep the leaves, covered, for
four or five minutes. "In that time, most of
the polyphenols will dissolve in the warm
water. If you boil it with the leaves in it, the
polyphenols may get oxidized and polymerized
and reduce their activity."
The researcher, who has been funded
by VA as well as the National Center for
Complimentary and Alternative Medicine
and National Cancer Institute, believes
military personnel may be at special risk
for skin cancer, given their increased
exposure to sunlight. That is part of what
motivated him to join VA in 2003 and conduct
research on behalf of veterans. More
than a decade earlier, his initial passion
for exploring natural cancer therapies had
centered on quite a different population:
mothers.
"I lost my mother to breast cancer,"
shared Katiyar. "I had done my PhD in
nutrition, and I realized that my parents
had devoted a lot of time and energy to
my education. Yet, I could not help my
mother. So I resolved to do something to
help all the other mothers who are still
here. I decided I would work on cancer—
how it can be prevented, particularly by
dietary supplements and nutrients."
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