"Drinking green tea still is good for you,” said Yu-Dong Zhou, a molecular biologist at the university's National Center for Natural Products Research. "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.”
The study examined the effect of high doses of the active ingredients in green tea extract on hypoxia-inducible factor-1, or HIF-1, a key regulator of how tumour cells adapt to low-oxygen conditions.
In recent years, several manufacturers have produced dietary supplements containing concentrated extracts of green tea's active ingredients.
The compounds are not toxic in large doses, but high concentrations may not necessarily be healthful, explained Dale Nagle, associate professor of pharmacognosy in the UM School of Pharmacy. Many commercial supplements provide far more of the active compounds than a person could obtain by simply drinking tea.
"The fact that the green tea ingredient known as ECG activates HIF-1 can have different effects depending on the type of tumour.
"The active compounds in green tea could actually serve dual functions, inhibiting HIF-1 at low concentrations and activating it at higher doses”, Zhou said.
"In theory, this effect on HIF-1 could suppress some early forms of tumours but may actually help other tumours - especially some of the more aggressive ones - survive and grow”, Nagle said.
Cautioning that the results are preliminary - the study was performed using cultured cells in test tubes - Zhou noted that taking extremely high doses of any dietary supplement is worrisome to researchers.
MEDICA.de; Source: University of Mississippi