Green Tea and Cancer
WebMD Live Events Transcript
Does green tea help in the
fight against cancer? The
American Institute of Cancer Research believes that those concerned about
lowering risk for cancer should consider adding green tea to a diet that is rich
in a variety of plant foods and low in fat and salt. However the FDA has refused
a request to label green tea as a cancer fighter. Thomas A. Gasiewicz, PhD,
helped us sort through the claims for and against the green tea cancer
connection on Aug. 18, 2005.
The opinions expressed herein are the guests' alone and have not been
reviewed by a WebMD physician. If you have questions about your health, you
should consult your personal physician. This event is meant for informational
Welcome to WebMD
Live, Dr. Gasiewicz. What is green tea and how it is different from what many people think of as tea -- little bags of "tiny little tea leaves."
Much of the differences in teas depend on the way the teas are processed. For example:
- White tea is very unprocessed, and likewise there's more beneficial chemicals or compounds associated with it.
- Green tea is a little bit more processed, it's been steamed a little bit more; oxidation of the chemicals occur.
- Black tea is the most processed of the tea leaves. The chemicals become more oxidized and there's fewer reported benefits from black tea than green or white tea.
What are some of the reported beneficial effects of green tea?
Most of the benefits reported center around green tea's anticancer activities. For example, effects upon breast cancer, prostate cancer, gastrointestinal cancer, colon cancer and stomach cancer have been reported in literature in populations who are consuming various amounts of green tea.
I should also point out that in some studies on humans
few if any effects from green tea on cancer have been see. There is really no
clear-cut evidence in studies on human populations, only suggestive evidence.
There's much experimental evidence from studies on animals, all pointing to a
beneficial effect of green tea and its components on the prevention of cancer. In those cases, the evidence is overwhelming and consistent in many experimental situations.
What conclusions can we draw from these studies?
|"Adding green tea or its components to an otherwise healthy diet seems very prudent." |
There are several difficulties in interpreting human studies, partly because there are many differences between humans that may make them more or less susceptible to the benefits of green tea. Some of these include:
- Genetic differences
- Sex differences (male versus female)
- Age differences
- The amount of green tea consumed
All these factors make interpretation of those studies very difficult, whereas in the experimental animal studies you have a genetically inbred group of animals that can be fed constant or varying amounts of green tea solutions or isolated compounds from green tea, and so we know exactly what these animals are being given.
As I said before, the evidence from these animal investigations are overwhelming, so going back to your question, it would be difficult for many of us scientists to believe all these benefits would occur only in animal studies. There are most likely benefits in human populations. Having said that, we don't know exactly how much green tea any one individual has to consume to have a protective or beneficial effect against certain types of cancer.
What's your opinion on The American Institute of Cancer Research's recommendation that those concerned about lowering risk for cancer should consider adding green tea to a diet rich in a variety of plant foods and low in fat and salt?
There is no evidence indicating that moderate consumption of green tea as a beverage or in things like pound cake, for example, has harmful effects, and, given the suggestive evidence from human population investigations and animal studies, there is certainly likely to be beneficial effects. So, adding green tea or its components to an otherwise healthy diet seems very prudent.
Why has the FDA refused to consider green tea as a cancer fighter when the American Institute of Cancer Research seems to think it would lower cancer risk for some?
Again, I think the firm data from human studies is not yet available. We need more clinical studies, we need studies on select populations where we can actually document the amount of green tea consumed and the type of cancers.