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Green tea may save lives, researchers find

Sept. 12, 2006
Courtesy JAMA
and World Science staff

Adults in Ja­pan who drank more green tea had a low­er risk of death from all causes and from heart dis­ease specif­i­cally, though not from can­cer, a study has found.

A de­pic­tion of the tea plant from Koehler's Me­dic­i­nal Plants, a col­lec­tion of of me­dic­i­nal plant draw­ings com­piled by Ger­man bot­a­nist Her­mann A. Köh­ler and pub­lished in 1887.

Tea is the world’s most con­sumed bev­er­age af­ter wa­ter, so even small health ef­fects could have ma­jor re­per­cus­sions for pub­lic health, ac­cord­ing to re­search­ers. 

Com­pounds in green tea called po­ly­phe­nols have been much stud­ied for pos­si­ble heart dis­ease- and can­cer-pre­ventive ef­fects. 

But al­though stud­ies with an­i­mals and cul­tured cells have shown pro­m­ise, the ef­fects in hu­mans re­main un­clear, said the sci­en­t­ists, Shi­ni­chi Ku­ri­ya­ma of the To­ho­ku Uni­ver­si­ty School of Pub­lic Po­l­i­cy in Sen­dai, Ja­pan, and col­leagues.

In the stu­dy, they tracked more than 40,000 ad­ults in north­east­ern Ja­pan, where green tea is pop­u­lar, from 1994 un­til last year. Par­tic­i­pants had no his­to­ry of stroke, cor­o­nary heart dis­ease or can­cer at the the stu­dy’s out­set, Kuriyama said.

Com­pared with par­tic­i­pants who drank less than one cup dai­ly, those who con­sumed five or more had an over­all risk of dy­ing 16 per­cent low­er dur­ing the time of the stu­dy, the re­search­ers re­ported. The re­duc­tion was 26 per­cent when on­ly the first se­ven years were counted.

The re­search­ers found no sig­nif­i­cant link be­tween green tea con­sump­tion and can­cer death. They al­so tested two oth­er types of tea, black and oo­long, and said they found lit­tle or no ev­i­dence link­ing them to re­duced mor­tal­i­ty. All three drinks are made from the tea plant Ca­mel­lia sinen­sis, but pro­cessed dif­fer­ent­ly.

The re­search­ers, re­port­ing their find­ings in the Sept. 13 is­sue of the Journal of the American Medical Association, wrote that the study isn’t the last word: still more ri­gor­ous tri­als will be needed to con­firm the re­sults. The ideal would be a “ran­dom­ized con­trolled tri­al” in which some par­ti­ci­pants are as­signed at ran­dom to drink the tea while others do not, Kuriyama wrote in an email. 

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Adults in Japan who drank more green tea had a lower risk of death from all causes and from heart disease specifically, though not from cancer, a study has found. The study appeared in according to a study in the September 13 issue of JAMA. But there was no link between green tea consumption and a reduced risk of death due to cancer. Tea is the world’s most consumed beverage in the world after water, so even small effects in humans could have large implications for public health, according to researchers. Compounds in green tea called polyphenols have been extensively studied for possible heart disease- and cancer-preventing effects. But although studies with animal studies and cultured cells have shown promise, the effects in humans remain unclear, said the scientists, Shinichi Kuriyama of the Tohoku University School of Public Policy in Sendai, Japan, and colleagues. In the study, they tracked more than 40,000 adults in northeastern Japan, where green tea is popular, from 1994 until last year. Participants had no history of stroke, coronary heart disease, or cancer at the beginning of the study, Kuriyama said. Compared with participants who consumed less than one cup daily, those who consumed five or more had an overall risk of dying 16 percent lower during the time of the study, the researchers reported. The reduction was 26 percent when only the first seven years of the study were counted, the scientists added. The researchers found there no significant association between green tea consumption and death from cancer. They also tested two other types of tea, black and oolong, and found little or no evidence linking them reduced mortality. All three teas are made from the tea plant Camellia sinensis, but processed differently. “Clinical trials are ultimately necessary to confirm the protective effect of green tea on mortality,” wrote Kuriyama and colleagues, who reported the results in the Sept. 13 issue of jama.