Adults in Japan who consumed higher amounts of green tea had a lower risk of death due to all causes and due to cardiovascular disease, 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 most consumed beverage in the world aside from water. Three billion kilograms of tea are produced each year worldwide, according to background information in the article. Because of the high rates of tea consumption in the global population, even small effects in humans could have large implications for public health. Among teas, green tea polyphenols have been extensively studied as cardiovascular disease (CVD) and cancer chemopreventive agents. Although substantial evidence from in vitro and animal studies indicates that green tea preparations may impede CVD and carcinogenic processes, the possible protective role of green tea consumption against these diseases in humans remains unclear.
Shinichi Kuriyama, M.D., Ph.D., of the Tohoku University School of Public Policy, Sendai, Japan, and colleagues examined the association between green tea consumption and mortality (death rate) due to all causes, CVD, and cancer within a large population. The study, initiated in 1994, included 40,530 adults (age 40 to 79 years) in northeastern Japan, where green tea is widely consumed. Within this region, 80 percent of the population drinks green tea and more than half of them consume 3 or more cups and day. The participants, who had no history of stroke, coronary heart disease, or cancer at baseline, were followed for up to 11 years (1995-2005) for all-cause death and for up to 7 years (1995-2001) for cause-specific death.
Over 11 years of follow-up, 4,209 participants died, and over 7 years of follow-up, 892 participants died of cardiovascular disease and 1,134 participants died of cancer. The researchers found that green tea consumption was inversely associated with death due to all causes and due to cardiovascular disease. Compared with participants who consumed less than 1 cup/d of green tea, those who consumed 5 or more cups/d had a risk of all-cause mortality and CVD mortality that was 16 percent lower (during 11 years of follow-up) and 26 percent lower (during 7 years of follow-up), respectively.
These inverse associations of all-cause and CVD mortality were stronger among women, although the inverse association for green tea consumption was observed in both sexes. In women, compared with those who consumed less than 1 cup/d of green tea, those who consumed 5 or more cups/d had a 31 percent lower risk of CVD death.
The researchers found there no significant association between green tea consumption and death from cancer. There were weak or neutral relationships between black tea or oolong tea and mortality.
"Clinical trials are ultimately necessary to confirm the protective effect of green tea on mortality," the authors write.
This study was supported by a Health Sciences Research Grant for Health Services, Ministry of Health, Labour, and Welfare, Japan.
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