Results of an early phase clinical study released in August by the Arizona Cancer Center indicate that green tea may help prevent cancer in humans.
The research shows that in some people, high doses of the green tea component epigallocatechin gallate (EGCG) increase the activity of a detoxification enzyme called glutathione S-transferase.
“”This particular detoxification enzyme is responsible for getting rid of toxic chemicals – carcinogens,”” said Dr. Sherry Chow, research associate professor at the Cancer Center and principal investigator for the study.
Prior studies on animals have demonstrated green tea’s detoxification properties, Chow said.
In the new study, 42 people were recruited and asked to refrain from consuming tea, she said.
After what Chow termed a “”washout period,”” the participants submitted blood and urine samples that were checked for the detoxification enzyme to establish a baseline level in each person.
The subjects of the study consumed four oral capsules of the green tea component EGCG daily for 28 days, Chow said.
Each capsule contained the equivalent extract of approximately 2-4 cups of green tea.
After four weeks, the subjects were tested again for levels of GST. The results were promising, Chow said.
“”After we analyzed the data we realized that this green tea component has the most dramatic effect on those who have low-baseline (GST) activities to start with,”” she said. “”This means it’s actually increasing the levels of those that have low detoxification enzyme capacity, which is good because those are the people that probably need this kind of protection.””
Those with low-baseline GST activity showed an increase of roughly 80 percent after 28 days of consuming EGCG, said Donna Vining, senior research nurse at the Cancer Center.
The participants with normal-to-high baseline levels of the detoxification enzyme did not show significant changes after taking the pills, Vining added.
The study does not prove that green tea prevents cancer, as further investigation is needed, Chow said.
“”Our institution actually has a number of ongoing clinical studies trying to look at the actual preventive activity of green tea in cervical cancer, in prostate cancer, as well as lung cancer,”” she said.
While researchers are hesitant to draw premature conclusions about the cancer-preventive potential of green tea, there are documented health benefits.
“”(Green tea) has been shown to lower cholesterol. It can be cardio-protective,”” said Chow, who drinks one cup per day, adding that she would drink more if not for the caffeine.
A Japanese company called Mitsui Norin supplied the study’s raw material, which was prepared using a water-extraction procedure. Some companies use an alcohol extraction, which can leave insecticides in the product, Vining said.
The green tea extract used in the study contained no caffeine, she said.
While green tea capsules are commercially available at health food stores and supermarkets, Vining said that most are not regulated for purity and content.
“”Even if you bought the same supplement from the same distributor month after month, the actual amount of active ingredient in it could vary widely,”” she said.
Cherrie Mannheim, owner of Espresso Art, 944 E. University Blvd., said that more customers ordered green tea after the results of a previous study touting its health benefits were released.
Mannheim said that it’s too early to tell if the most recent study’s publication has generated an increase in green tea sales at her business, but said she anticipated it would.
“”Word is spreading like wildfire,”” she said.
White, green and black teas come from the same plant, camellia sinensis. The difference is that white tea is unfermented, green is partially fermented and black is more fermented, Vining said.
The results of the study, funded by the National Cancer Institute, were published under the title “”Modification of Human Glutathione S-Transferases by Polyphenon E Intervention”” in the August issue of Cancer Epidemiology Biomarkers and Prevention, a journal of the American Association for Cancer Research.
“”I think the study basically shows that, for the first time in people, that (by) consuming this high amount of green tea extract, we actually can induce these detoxification enzymes, and possibly will have some cancer-preventive potential,”” Chow said.
