A growing number of people are drinking green tea because of its supposed anti-cancer properties, but people who take concentrated tea extract supplements should exercise care. A study by researchers at the University of Mississippi suggests that very high doses of green tea extract may actually activate - rather than shut down - the genetic mechanisms that help certain tumors survive and grow. Green tea is a popular beverage throughout much of the world and has been used medicinally for centuries in Asia. In areas where people drink a lot of green tea, there is a lower incidence of heart disease and some cancers. Hoping to improve upon the natural product, several manufacturers have produced dietary supplements containing concentrated extracts of green tea's active ingredients.
"Drinking green tea still is good for you," said researcher Yu-Dong Zhou. "There are thousands of years of evidence on that, but the idea of taking the equivalent of hundreds of cups of tea a day is something that needs to be looked at carefully." Zhou is the lead investigator of the study, published in the Journal of Natural Products.
Co-researcher Dale Nagle said that the concentrated compounds are not toxic in large doses, but high concentrations may not necessarily be healthful. "Nearly all the evidence of the beneficial effects of green tea comes from studies on populations who consume green tea, not tea extract in the form of powder, concentrates or pills," Nagle explained. "There is no direct evidence that taking reasonable quantities of these green tea products is toxic. But the issue here is whether these extremely high doses are really beneficial."
The researchers believe that the active compounds in green tea could actually serve dual functions, inhibiting the tumor regulators at low concentrations and activating them at higher doses. "At low concentrations, it doesn't seem to have this potentially negative effect as we saw in the lab," Nagle said. "A lot more study needs to be done to see what the outcome will be in people who take high doses of these compounds."
