The researchers at the Tohoku University School of Public Policy in Sendai, Japan, said that tea is the world's most consumed beverage after water, so even small health effects could have major repercussions for public health.
Compounds in green tea called polyphenols have been much studied for possible heart disease and cancer preventive effects. But although studies with animals and cul-tured cells have shown promise, the effects in humans remain unclear, said Shinichi Kuriyama, the lead researcher on the study.
The study, initiated in 1994, included 40,530 adults (age 40 to 79 years) in northeast Japan, where green tea is widely consumed. Within this region, 80 per cent 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.
Compared with participants who consumed less than 1 cup per day of green tea, the risk of all-cause mortality and cardiovascular disease mortality that was 16 % lower (during 11 years of follow-up) and 26 % lower (during 7 years of follow-up), respectively for those who consumed 5 or more cups per day.
The researchers found 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.
The authors wrote, "Clinical trials are ultimately necessary to confirm the protective effect of green tea on mortality."
