Ingredients in Green Tea Can Protect Against Cancer, Heart Disease
WebMD News Archive
In one widely publicized study, researchers at the Case Western Reserve
University School of Medicine, in Cleveland, reported that an ingredient in the
polyphenols in green tea kills cancer cells while sparing healthy cells. In the
study, reported in the Dec. 17, 1997, issue of the Journal of the National
Cancer Institute, the researchers tested this ingredient, EGCG, on
cancerous human and mouse cells of the skin, lymph system, and prostate and on
normal human skin cells. They found that EGCG caused cell death in cancer cells
while leaving healthy cells unharmed.
Purdue University (West Lafayette, Ind.) researchers Dorothy Morre and D.
James Morre reported in December 1998 at the 38th annual meeting of the
American Society for Cell Biology in San Francisco, that EGCG inhibits an
enzyme called NOX. This enzyme helps carry out several cell functions and is
required for growth in both normal and cancerous cells. The overactive and
cancer-causing form of NOX is known as tNOX.
"Our research shows that green tea leaves are rich in this anti-cancer
compound, with concentrations high enough to induce anti-cancer effects in the
body," Dorothy Morre, professor of foods and nutrition in Purdue's School
of Consumer and Family Sciences, tells WebMD. "Drinking more than four cups
of green tea a day," she says, "could provide enough of the active
compound to slow and prevent the growth of cancer cells. Granted, for most
people that's a lot of tea."
There have been other studies on tea's effect on heart disease. As Yang
points out, these studies show that tea polyphenols inhibit the oxidation of
LDL, the "bad" cholesterol.
No one is saying, yet, that drinking green tea cures cancer or heart disease
in humans. In fact, in testing tea's effects, researchers have used a strong
concentration -- about 100 times what the Lipton Company estimates is in one
cup of tea. More laboratory research plus human studies are needed to see
whether extracts of green tea can be effective as drugs to prevent cancer and
stop prostate and other tumors from growing.
Yang says that if in fact tea does, people would need to slurp 3-10 cups a
day for maximum protection from common forms of cancer. He says this in itself
may be harmful. "Ingestion of large amounts of tea may cause nutritional
and other problems because of the caffeine and the strong binding activities of
tea polyphenols," notes Yang, who is with the Laboratory for Cancer
Research at Rutgers University, in Piscataway, N.J.
Elizabeth Kaegi, MB, reporting in 1998 on behalf of the Task Force on
Alternative Therapies of the Canadian Breast Cancer Research Initiative, says
that while she believes moderate consumption of green tea appears safe,
"because excess caffeine can cause nervousness, insomnia, and
irregularities in heart rate, pregnant women, nursing mothers, and patients
with cardiac problems are usually advised to limit their intake to two
cups." Kaegi is the former director of Medical Affairs and Cancer Control
at the National Cancer Institute of Canada and the Canadian Cancer Society.