Green tea has been sipped for centuries in Asia, where it is used to treat anything from headaches and depression to arthritis and cancer. Within the last 20 years, scientific studies have found evidence for some of these claims. Some researchers believe green tea may prevent cancer, although the U.S. government is wary.
For tea-drinkers all over the world, this sound means another cup of their favorite beverage is ready to enjoy. But a growing body of research suggests that some teas may do more than than just please the palate. According to the American Institute for Cancer Research, drinking just a few cups of green tea daily can help prevent tumors. Spokesman Jeffrey Prince summarized the researchers' conclusions at a recent Washington meeting:
"The scientists we have brought together this year are talking about green tea. We seem to be getting some results about green tea. The studies have been accumulating and we're moving toward a greater understanding." Prince said. "Basically we think that people concerned with reducing cancer risk should consider adding green tea as one more potentially protective ingredient in a diet rich in plant foods."
Population studies have found reduced cancer rates in Asian countries where green tea is a major part of the diet. Scientists do not know what makes the tea so beneficial, but they have some promising theories. Most of their ideas involve powerful compounds called catechins that make up nearly one-third of green tea's dry weight.
University of Rochester researcher Thomas Gasiewicz says other teas have catechins, but the green variety has the most because its leaves are simply picked and preserved.
"Black tea and, actually, oolong contain some of these things as well, because some of the different varieties in terms of black tea, oolong tea may come from the exact same tea leaf, but the concentrations are much less because of the oxidation and processing of the tea leaves that occurs." Gasiewicz said.
Mr. Gasiewicz is particularly interested in a catechin in green tea called EGCG. His research suggests that EGCG can stop cancer before it starts, but he does not know how. He thinks the EGCG may target and block a particular protein in many cells that would otherwise interfere with genetic material and cause cancer.
"This particular research, as well as other research that's being done, indicates that we can find a mechanism whereby these things are actually working, so we can block cancer and cancer-causing agents."he said.
But not everyone agrees. U.S. government food and drug regulators believe insufficient evidence exists to prove that green tea prevents cancer. The Food and Drug Administration says some studies supporting the claim are weak. It concludes that, based on the limited research available, green tea is highly unlikely to reduce the risk of prostate, breast, or any other type of cancer.
Mr. Gasiewicz acknowledges that research on humans is inconclusive, but he is confident in the results of other studies.
"The epidemiology data are not very clear. There's a variety of difficulties in doing those studies. However, the animal data is very, very consistent among all different types of carcinogens, and it's hard for me to believe that at least at some dose there would not be a protective effect for human populations." Gasiewicz said.
Although data on proper dosage is lacking, Jeffrey Prince of the American Institute for Cancer Research says nothing suggests that green tea is dangerous.
"It is likely that moderate consumption won't hurt us a bit, and could, science may soon show, offer us considerable benefits." he said.
Mr. Prince says that green tea is most effective as part of a diet high in fruits and vegetables, which contain other compounds thought to reduce the risk of cancer. A joint board of the American Institute for Cancer Research and the World Cancer Research Fund estimated that diets like this could eliminate three to four million cases of cancer each year. As for green tea, they recommend drinking up to half a liter each day.