Populations of counties where green tea is consumed as part of the every day diet, such as Japan and China, tend to have a lower incidence of cancer than people in countries where green tea is less commonly drunk. Consequently, green tea catechins - antioxidant polyphenols - have been the focus of considerable research in recent years. Researchers from the University of Arizona, led by research associate professor H-H Sherry Chow, set out to explain the anti-cancer effect of green tea by seeing if a concentrate of catechins had any effect on levels of glutathione S-transferase (GST) enzymes. GSTs are understood to modify cancer-causing molecules so they do not damage cellular DNA. They believe their findings suggest a green tea concentrate could enable some people to strengthen their metabolic defence against carcinogens, thereby providing a new layer of evidence to support the green tea category of supplement and food ingredients. The study involved 42 healthy volunteers, who abstained from consuming tea or tea-related products in the four-weeks prior to commencement. They then gave a fasting blood sample, and plasma and lymphocytes were isolated for analysis of GST activity and level. For the next four weeks the participants all consumed a standardized Polyphon E preparation at a dose of 800mg epigallocatechin gallate (EGCG) per day on an empty stomach. Polyphenon E is commercially available and made by Japan's Mitsui Norin. At the end of the four weeks, the participants again gave blood samples. The researchers found that GST activity increased when all the results were taken together, from 2252.9 plus/minus 734.2 ng/mg protein to 2634.4 plus/minus 1138.3 ng/mg protein. But the increase was most pronounced in people who had low GST activity in the beginning. In these people, GST activity was seen to increase by as much as 80 per cent. "Expression of this enzyme varies dramatically in people due to genetic variation and environmental factors," explained Chow. In people with low GST levels there was no change, and in those who had high levels there was some evidence of a decrease at the end of the four-week trial - although the researchers explained this as being down to "random variation". "Green tea catechins somehow increase gene expression of these enzymes, which can be an advantage to people with low levels to start with," said Chow. "There may be other mechanisms in play by which green tea may protect against cancer development, but this is a good place to start." Reference: Journal: Cancer Epidemiology Biomarkers & Prevention DOI: 10.1158/1055-9965.EPI-06-0830 Title: "Modulation of Human Glutathione S-Transferases by Polyphenon E Intervention" Authors: H-H Sherry Chow, Iman Hakim, Donna R Vining, James Crowell, Margaret E Tome, James Ranger-Moore, Catherine A Cordova, Dalia M Mikhael, Margaret M Briehl and David S Alberts.
