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You're listening to ALL THINGS CONSIDERED from NPR News. For some time, experts have been reading tea leaves - green tea leaves. Over the years, science has looked into whether green tea helps prevent heart disease, even cancer. Many of these studies have been served tepid, full of caveats. And the tea has often been tested on small animals. Well, now from Japan comes this news. Drinking green tea may lower the risk of death, especially from heart disease. And that is in people, not in hamsters. NPR's Patricia Neighmond reports on the study in this week's Journal of the American Medical Association.

PATRICIA NEIGHMOND: The study took place in northeastern Japan, where 80 percent of the population drinks green tea. Researchers looked at over 40,000 adults, comparing those who drink less than one cup of tea a day to those who drink three to five cups a day. Over eleven years, those who drank more tea were less likely to die of heart disease. Epidemiologist Shinichi Kuriyama from Tohoku University School of Medicine headed the study.

Dr. SHINICHI KURIYAMA (Epidemiologist, Tohoku University): Our findings might explain differences in mortality profile between Japan and the U.S. Now Japanese has the longest longevity in the world.

NEIGHMOND: In the study, women saw a greater decrease in heart disease than men. For women who drank five or more cups of green tea daily, there was a 31 percent lower risk of death from heart disease. For men, the risk was reduced by 22 percent. For both men and women, the biggest decrease was in death due to stroke. Dr. Kuriyama.

Dr. KURIYAMA: We didn't know the mechanism of green tea in our study, but recent evidence shows that hypertension or cholesterol or atherosclerosis itself could be improved by drinking green tea.

NEIGHMOND: Although Kuriyama's study did not specifically look at hypertension, cholesterol or atherosclerosis, Kuriyama speculates that certain antioxidants in green tea help keep arteries healthy. Green tea is made by a more simple process than black tea. With green tea, leaves are steamed immediately after picking them. With black tea, moisture is removed. Tea leaves are fermented in humidity-controlled room and then dried, a longer process that may remove some antioxidants. Joe Vincent is a biochemist at the University of Scranton in Pennsylvania who studies antioxidants in food. Vincent says the results of the study are important, but not at all conclusive.

Mr. JOE VINCENT (Biochemist, University of Scranton): To me, it's not cause and effect. It's a hint that green tea is good for the heart.

NEIGHMOND: To solidly establish cause and effect, Vincent says a rigorous, long-term clinical trial would be needed. And in any case, Vincent says all tea - both black and green - may help arterial health by increasing the body's natural production of nitric oxide, which makes arteries more flexible.

Mr. VINCENT: It makes your arteries be able to constrict and open up again more easily, with less changes in your blood pressure. Less stress on your heart.

NEIGHMOND: So bottom line, it can't hurt - says Vincent - to drink more tea both black and green, both hot and cold. Americans traditionally are not tea drinkers, although that's changing somewhat with the increase in cold, bottled green tea beverages. And interestingly, Japanese researcher Kuriyama recommends cold tea because he says some studies have implicated hot beverages in esophageal cancer. In his study, Kuriyama found no link between drinking green tea and reduced death due to cancer as other studies have suggested. Patricia Neighmond, NPR News.

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