Drink Up! More Evidence for the Power of Green Tea

Author:  Merolla Lisa

Date:  August 2007

In exploring the benefits of green tea, researchers at the Arizona Cancer Center determined that chemicals from the drink can increase the level of key detoxification enzymes in humans. Because these enzymes help rid the body of toxins, the increase could explain why green tea seems to play a role in preventing cancer. The research was published in the August issue of Cancer Epidemiology, Biomarkers & Prevention.

The researchers found that Polyphenon E, an extract composed of antioxidants from green tea known as green tea catechins, greatly increases the amount of glutathione S-transferase (GST) enzymes in people with naturally low levels of the proteins. GST is a type of detoxification enzyme which is thought to help the body defend against cancer-causing toxins. These enzymes work by altering cancer-causing molecules, or carcinogens, enough to make them inert.

"They actually convert known carcinogens to non-toxic chemicals, and studies have shown a correlation between deficient expression of these enzymes and increased risk of developing some cancers," lead researcher H-H Sherry Chow explained.

The study involved 42 people and began with a four week "wash-out period" during which the volunteers abstained from all tea products. Researchers then drew blood and measured GST enzyme levels for each participant. Serving as the baseline GST levels, these values varied widely from person to person.

Over another four weeks, volunteers continued to avoid tea, while also taking four Polyphenon E capsules, each of which delivered the equivalent of eight to sixteen cups of green tea. The researchers then determined the new GST enzyme levels. While people with naturally mid to high amounts of GST were not significantly affected, those with originally low levels experienced a considerable increase in the proteins – up to 80 percent.

This rise in GST production could explain green tea's cancer-resisting qualities. "This is the first clinical study to show proof that chemicals in green tea can increase detoxification enzymes in humans," Chow said. "There may be other mechanisms in play by which green tea may protect against cancer development, but this is a good place to start."

This research was sponsored by the National Cancer Institute, which currently is backing various scientific studies into the potential benefits of green tea.

By Lisa Merolla