Cancer and Green Tea

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 purposes only.

MODERATOR:
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."

GASIEWICZ:
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.

MODERATOR:
What are some of the reported beneficial effects of green tea?

GASIEWICZ:
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.

MODERATOR:
What conclusions can we draw from these studies?

"Adding green tea or its components to an otherwise healthy diet seems very prudent."

GASIEWICZ:
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.

MODERATOR:
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?

GASIEWICZ:
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.

MEMBER QUESTION:
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?

GASIEWICZ:
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.

Something else to consider: Green tea consumption may not have a beneficial effect for all cancers. There was a report that came out a few weeks ago (covering a population in Singapore) that green tea consumption had some beneficial effects for protecting against the development of breast cancer in a defined population that was genetically more susceptible to developing breast cancer.

MODERATOR:
What types of cancer have been mentioned in relationship to green tea?

GASIEWICZ:
In human populations, the types of cancers mentioned include:

  • Breast cancer
  • Prostate cancer
  • Skin cancer
  • Cancers of the gastrointestinal tract

In experimental animals, as I said previously, the data is overwhelming for protection against a variety of cancers, including skin, lung, liver, gastrointestinal tract, pancreas, bladder, and breast cancer.

MEMBER QUESTION:
Have you noticed any difference in health virtues between high-quality green tea and more processed green teas? For example, whole green tea leaves vs. green tea extract?

"Many nutritional agencies recommend four to five cups of green tea per day."

GASIEWICZ:
There's not enough research I'm aware of to indicate any differences.

Although epigallocatechin gallate (EGCG) is a green tea chemical reported to have most of the beneficial effects, I think its concentration in capsule form would likely be higher and the absorption from the gastrointestinal tract may also be higher. So, more likely beneficial effects are associated with those green tea forms that contain higher concentrations of EGCG.

MEMBER QUESTION:
What is it in green tea that fights cancer?

GASIEWICZ:
Organic compounds, called catechins, seem to have most of the beneficial effects. Under experimental situations, EGCG -- one of the family of catechins -- is the one that seems to have many of the potent anticancer effects.

MEMBER QUESTION:
How often should one drink green tea to receive benefits?

GASIEWICZ:
A very good question to which we do not have a precise answer. Many nutritional agencies recommend four to five cups per day added to a regular, healthy diet. But again, the actual benefits may vary between individual; precisely what one individual needs as compared to another we don't know for certain.

MEMBER QUESTION:
Is there caffeine in green tea?

GASIEWICZ:
Yes, there is some caffeine in green tea, but I believe one can get decaffeinated green tea, too.

MEMBER QUESTION:
Is Lipton's claim of antioxidants in its low-quality black tea meaningful?

GASIEWICZ:
Yes. All teas contain beneficial compounds: the catechins as well as antioxidants. However, the less processed teas, such as the green or white tea, contain higher concentrations of the beneficial compounds than the more processed black teas. Nevertheless, there are clearly beneficial compounds in black tea, too.

MEMBER QUESTION:
Will green tea lower the risk of returning cancer for those of us who are cancer survivors?

GASIEWICZ:
That's a great question. I wish I knew the answer, I wish someone knew the answer.

"We need more research...on green tea as an anticancer treatment."

We certainly need more research not only on the beneficial effects of green tea for cancer prevention, but on green tea as an anticancer treatment -- in other words, for someone who already has cancer. The benefits to these particular individuals, we don't yet know.

MEMBER QUESTION:
In countries where green tea is part of the culture and routine, do you know how often green tea is consumed?

GASIEWICZ:
From what I understand, green tea or its components in different forms, may be consumed many times during the day.

MEMBER QUESTION:
The Japanese drink lots of green tea, but they also get it in gum, candy, ice cream -- they even use it as a sauce. What's the most efficient way to take advantage of the possible health benefits?

GASIEWICZ:
Another good question for which we don't have precise answers. These chemicals are absorbed from the gastrointestinal tract very readily, so either in consumption as a beverage, as part of gum or some other food type, I think all have benefits.

I don't think we know exactly what the relative absorption is when these beneficial compounds are associated with different food types. Also, what they call the half life of these chemicals in humans is relatively short, on the order of several hours. So consuming these products containing catechins or green tea throughout the day rather than at one particular time of the day, would likely to have more of a beneficial effect.

MEMBER QUESTION:
What foods can you eat that have green tea in them?

GASIEWICZ:
There have been many recipes containing green tea compounds and crushed green tea leaves. Some of these recipes are green tea pound cake, dip, and sorbet .

MEMBER QUESTION:
Do you get the maximum health benefit if you eat foods with green tea in them?

GASIEWICZ:
That depends. Some foods with very high fiber, for example, may cause some of the beneficial chemicals in green tea, like the catechins, to be attached to the fiber and not readily absorbed. So while fiber is certainly excellent for you and an important part of your diet, in many cases fiber may actually hinder absorption of these beneficial chemicals.

That's why some people believe, although I don't think it's been proven, one of the most beneficial ways to consume these chemicals is through the beverage. However, if these beneficial chemicals can be put into other food items like dips or pound cakes, for example, that would also increase our exposure to them, which of course would likely increase our beneficial effect. By the way, jasmine tea is a type of green tea and of course, contains the beneficial chemicals found in other types of tea.

MEMBER QUESTION:
Does it matter how much green tea we add to a healthy diet?

GASIEWICZ:
Many nutritional agencies recommend four to five cups per day added to a healthy diet. However, consumption of greater amounts, say 10 to 12 cups per day, while it may increase your exposure to the beneficial chemicals, it may also cause undesired effects, such as diarrhea.

No major bad effects have been reported, but, like consuming large amounts of any other liquids such as coffee or soda, for example, many people experience diarrhea.

MEMBER QUESTION:
Do people in Far East Asian countries have lower incidences of cancer?

GASIEWICZ:
Yes, but it's not clear that it's because of their green tea consumption. Many Asian countries do not have a diet like we have in the West, which is high in fat and calories, for example. There are also genetic differences between Japanese and Caucasians which may make them less or more susceptible to certain types of cancer.

So even though there are clear differences between the cancer incidence in Japanese or other Asian populations as compared to the United States, again it is not clear at all that this is due to consumption of green tea, and there are many, many other factors to be considered.

"Studies are being done on the beneficial effects of green tea on humans who regularly consume it." "We need more research...on green tea as an anticancer treatment."

MEMBER QUESTION:
I am allergic to green tea; it makes me nauseous. Is there a way I can incorporate green tea into my diet through other methods?

GASIEWICZ:
If you are allergic to some of the chemicals in green tea when consumed as a beverage, there is a good possibility you will experience similar allergic reactions when consuming it in any food. You really should consult your doctor before consuming green tea.

MEMBER QUESTION:
Are more studies being done on green tea?

GASIEWICZ:
Yes. Studies are being done on the beneficial effects of green tea on humans who regularly consume it. There are experimental studies being done on animals to determine what types of cancer are affected. There are studies attempting to develop compounds similar to those in green tea that could be anticancer agents for those developing or who have cancer.

MODERATOR:
Dr. Gasiewicz, do you have any final comments for us?

GASIEWICZ:
Adding green tea to a healthy diet (as a beverage or in foods), along with exercise, is a great way to go.

MODERATOR:
Remember to take a look at the green tea recipes we've provided with this chat, too. Goodbye and good health.



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Reviewed on 9/26/2005 9:38:11 PM

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