Apr. 9, 2002 San Francisco, April 8 — People who drink tea may be doing more than soothing a weary stomach—they might be preventing cancer, according to researchers at the Keck School of Medicine of USC and colleagues.
Certain tea-drinkers in a study conducted in Shanghai, China were about half as likely to develop cancer of the stomach or esophagus as similar study participants who showed little evidence of tea drinking, researchers said. The team, which includes scientists from Rutgers University and Shanghai Cancer Institute, presented results of the ongoing investigation at the 93rd annual meeting of the American Association for Cancer Research.
In a study beginning in 1986, researchers followed 18,244 men ages 45 to 64 in the eastern Chinese coastal city and found 190 cases of gastric cancer and 42 cases of esophageal cancer. The researchers compared the cancer patients to 772 similar men without cancer.
They measured levels in each participant of certain chemicals, called polyphenols, that are present in tea. They also checked for levels of several chemicals produced when polyphenols breakdown in the body. Polyphenols included epigallocatechin (EGC) and epicatechin (EC).
The team found that the presence of EGC in urine was associated with a lower risk of gastric and esophageal cancer, after adjusting for smoking, alcohol drinking, carotenes (natural chemicals found in carrots, spinach and other vegetables and fruit) and H. pylori (a type of bacteria linked to peptic ulcers).
Cancer-protective effects were mostly seen in people who had lower-than-average levels of carotenes in their blood. Carotenes themselves are believed to reduce risk of cancer and other diseases.
"This study provides direct evidence that tea polyphenols may act as chemopreventive agents against gastric and esophageal cancer development," says Mimi C. Yu, Ph.D., professor of preventive medicine at the Keck School of Medicine and member of the research team.
All varieties of tea come from the leaves of a single plant, Camellia sinensis. This evergreen contains some of the most powerful antioxidants known.
The human body constantly produces oxidants, rogue molecules that, having lost an electron, are extremely unstable and chemically reactive. To become stable, oxidants steal electrons from other molecules in the cell. In the process, they damage critical cell proteins and genetic material. To protect itself, the body makes and uses antioxidants, which scavenge and seize oxidants.
It is thought that under a state of imbalance, or oxidative stress, cells may mutate and contribute to disease processes, including cancer.
But tea contains antioxidants—the polyphenols called catechins—that have been shown to be as powerful as the well-established antioxidants vitamins C and E at protecting proteins and DNA from oxidative damage.
Green tea contains the most catechins, followed by oolong and black teas. In research studies, catechins have been shown to halt tumor cell growth as well as to protect healthy cells from damage.
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