In one widely publicized study, researchers at the Case Western Reserve University School of Medicine, in Cleveland, reported that an ingredient in the polyphenols in green tea kills cancer cells while sparing healthy cells. In the study, reported in the Dec. 17, 1997, issue of the Journal of the National Cancer Institute, the researchers tested this ingredient, EGCG, on cancerous human and mouse cells of the skin, lymph system, and prostate and on normal human skin cells. They found that EGCG caused cell death in cancer cells while leaving healthy cells unharmed.
Purdue University (West Lafayette, Ind.) researchers Dorothy Morre and D. James Morre reported in December 1998 at the 38th annual meeting of the American Society for Cell Biology in San Francisco, that EGCG inhibits an enzyme called NOX. This enzyme helps carry out several cell functions and is required for growth in both normal and cancerous cells. The overactive and cancer-causing form of NOX is known as tNOX.
"Our research shows that green tea leaves are rich in this anti-cancer compound, with concentrations high enough to induce anti-cancer effects in the body," Dorothy Morre, professor of foods and nutrition in Purdue's School of Consumer and Family Sciences, tells WebMD. "Drinking more than four cups of green tea a day," she says, "could provide enough of the active compound to slow and prevent the growth of cancer cells. Granted, for most people that's a lot of tea."
There have been other studies on tea's effect on heart disease. As Yang points out, these studies show that tea polyphenols inhibit the oxidation of LDL, the "bad" cholesterol.
No one is saying, yet, that drinking green tea cures cancer or heart disease in humans. In fact, in testing tea's effects, researchers have used a strong concentration -- about 100 times what the Lipton Company estimates is in one cup of tea. More laboratory research plus human studies are needed to see whether extracts of green tea can be effective as drugs to prevent cancer and stop prostate and other tumors from growing.
Yang says that if in fact tea does, people would need to slurp 3-10 cups a day for maximum protection from common forms of cancer. He says this in itself may be harmful. "Ingestion of large amounts of tea may cause nutritional and other problems because of the caffeine and the strong binding activities of tea polyphenols," notes Yang, who is with the Laboratory for Cancer Research at Rutgers University, in Piscataway, N.J.
Elizabeth Kaegi, MB, reporting in 1998 on behalf of the Task Force on Alternative Therapies of the Canadian Breast Cancer Research Initiative, says that while she believes moderate consumption of green tea appears safe, "because excess caffeine can cause nervousness, insomnia, and irregularities in heart rate, pregnant women, nursing mothers, and patients with cardiac problems are usually advised to limit their intake to two cups." Kaegi is the former director of Medical Affairs and Cancer Control at the National Cancer Institute of Canada and the Canadian Cancer Society.