August 21, 2007
TUCSON, Ariz.Polyphenols from green tea appear to boost production of a group of detoxification enzymes in people with low levels of the compounds, possibly strengthening metabolic defenses against carcinogenic toxins, according to researchers from the Arizona Cancer Center and University of Arizona.
In the study, supported by the National Cancer Institute (NCI), researchers recruited 42 healthy volunteers, who underwent a four-week washout period, refraining from tea or tea-related products. Fasting blood samples were taken at the end of the washout period to assess activity and levels of glutathione S-transferases (GST), a major group of detoxification enzymes. Participants then underwent four weeks of green tea polyphenol intervention in the form of a standardized preparation (Polyphenon E) delivering 800 mg/d of epigallocatechin gallate (EGCG). The level of green tea catechins was equivalent to consuming between eight and 16 cups of green tea.
The intervention enhanced GST activity in blood lymphocytes from 30.7 ± 12.2 to 35.1 ± 14.3 nmol/min/mg protein. There was a statistically significant increase in GST activity among individuals whose baseline activity was in the lowest tertile. However, there was a statistically significant decrease in GST activity in individuals whose baseline activity was in the highest tertile; researchers attributed the decrease to random variation. The researchers concluded green tea polyphenols may enhance the detoxification of carcinogens in individuals with low baseline detoxification capacity.
This is the first clinical study to show proof that chemicals in green tea can increase detoxification enzymes in humans, according to the studys lead investigator, H.-H. Sherry Chow, Ph.D. There may be other mechanisms in play by which green tea may protect against cancer development, but this is a good place to start.
The study was published in the August issue of Cancer Epidemiology, Biomarkers & Prevention (2007;16(8):1662-6) (DOI:10.1158/1055-9965.EPI-06-0830).
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