NEW YORK (Reuters) -- A powerful antioxidant ingredient in green tea kills human cancer cells in laboratory experiments, according to a report in the Journal of the National Cancer Institute for December 17.
Tests of the ingredient, called epigallocatechin-3-gallate, showed it killed cancer cells in samples of skin, lymph system, and prostate tissue taken from both humans and mice while leaving healthy cells unharmed, report researchers from Case Western Reserve University in Cleveland, Ohio.
Exactly how the tea ingredient works against cancer remains unclear, says Dr. Hasan Mukhtar, senior study author and professor of dermatology at the university. But he notes that the compound leads to the programmed cell death, or apoptosis, of cancer cells.
"It seems that somehow, through a cell-cell signaling pathway, it is communicated to the cancer cells that they better commit suicide or they'll be murdered," the researcher says. "So cells make a decision and undergo apoptosis. And we don't know the signaling pathway."
Mukhtar says evidence of apoptosis showed up as "very distinct, clear-cut features in the shape of the cells" and in the breakdown of their molecular structure. At the highest dose of the green tea ingredient, nearly all cells were found to be in the latest stages of apoptosis.
The researcher says the new findings add to previous test-tube studies showing that the tea ingredient prevented tumors in animal tissue. Dietary studies of tea consumption in people also suggest that green tea has some cancer preventive properties.
"Some nutritional epidemiology studies have suggested that green tea consumption might be effective in the prevention of certain human cancers -- cancers of the bladder, prostate, esophagus, and stomach," he says. "For example, one hospital in Shanghai reported that the recurrence of esophageal cancer was low in that part of the population that was drinking green tea."
Mukhtar and his colleagues point out that green tea accounts for about 20% of global tea consumption, with black tea making up most of the rest. "Tea consumption in the world is very high and ranks second to water consumption," they state.
The researcher notes that a cup of green tea contains between 100 and 200 milligrams of the anti-tumor ingredient. Does he advocate drinking green tea for cancer prevention? "Yes," he says. "Based on our studies and others, it seems consumption of four cups of green tea per day should be sufficient," he says.
The researchers say study findings also warrant clinical trials on the green tea ingredient in people at high risk for cancer. SOURCE: Journal of the National Cancer Institute (1997;89(24):1881-1886)