Cancer - Green Tea May Curb Cancer
Green Tea May Curb Cancer
A Swedish study has thrown light on the mystery surrounding the therapeutic effects of green tea -- a puzzle that has intrigued scientists for years.
Several recent studies have shown an association between a lower incidence of cancer and consumption of green tea . This beverage is consumed in nations with lower cancer rates than the United States, such as Japan, China and India. But there has been no clear evidence demonstrating the mechanism by which green tea may prevent cancer.
Now an article published in the April 1 issue of the international journal, Nature, points to the effects of one of green tea components _ a substance called epigallocatechin-3-gallate, or EGCG _ as preventing the growth of new blood vessels. This process, called angiogenesis, is particularly significant in the development of tumors.
Yihai Cao and Renhai Cao of the Karolinska Institute in Stockholm, Sweden, examined one group of four mice that had consumed green tea as their sole drinking fluid and a second group of four mice that drank water instead.
The researchers used gene therapy to stimulate corneal neovascularization, which is abnormal growth of blood vessels covering the cornea, the transparent dome on the surface of the eye. Researchers used three measurements of blood-vessel growth to compare the corneas of the two groups. They found that, depending on the method used, the green-tea-drinking mice had between 35 percent to 70 percent less blood-vessel growth than the water-drinking-mice. These results suggest that EGCG's role in preventing the growth of new blood vessels could be key to understanding green tea association with lower cancer incidence, according to the researchers.
Unlike black tea, leaves used to make green tea do not undergo fermentation, a process that alters the chemical structure of the tea leaf. green tea contains polyphenols, chemicals that are believed to act as powerful antioxidants . antioxidants protect cells from the effects of oxygen, which can cause abnormal changes in the genetic material of cells.
Studies demonstrating the beneficial effects of green tea include a 1994 comparison between green-tea drinkers and non-green-tea drinkers in Shanghai, China. Researchers from the Shanghai Cancer Institute and the National Cancer Institute in Bethesda, Md., found that green-tea drinking was linked to a 60-percent reduction in cancer of the esophagus among men and women who did not smoke.
But not all studies of green tea show positive results. According to an analysis of 28 human studies of green tea and cancer published last year in the international journal Nutrition and Cancer, 17 studies showed a link between green-tea drinking and decreased cancer rates, while seven demonstrated a higher cancer risk for green-tea drinkers. An additional five of the 28 studies showed a greater cancer risk if the tea was consumed at a high temperature.
But because green tea has no confirmed side effects, many physicians are open to recommending it.
Dr. Katherine pisters of the University of Texas M.D. Anderson Cancer Center in Houston is currently conducting a clinical trial of green tea on patients who have not responded to chemotherapy. 'There are some promising studies on green tea, but there is no guarantee that this is an effective treatment,' she said.