Green Tea Consumption and Mortality among Japanese Elderly People: The Prospective Shizuoka Elderly Cohort
Introduction
Green tea has been extensively studied for its potential preventive and therapeutic roles, especially for cardiovascular disease (CVD) and cancer 1, 2. In vitro and animal studies have provided strong evidence that tea polyphenols, including the catechins found predominantly in tea, may be sufficiently bioreactive to affect the pathogenesis of these chronic diseases 1, 2, 3, 4, 5. Epidemiological studies, however, have yielded inconsistent results concerning the associations between green tea and health, and thus, the effects of green tea remain unclear in humans 1, 2, 6, 7, 8, 9, 10, 11, 12, 13, 14.
In a recent cohort study in Miyagi, Japan (10), green tea consumption was shown to be associated with reduced all-cause mortality and CVD, but not with reduced mortality from cancer. One potential limitation of this study is the lack of a group which drank large amounts of green tea as the highest category only consumed five or more cups per day. This may have resulted in the moderate effects on reduced all-cause mortality and CVD as well as in the null association between green tea and cancer mortality (15). Furthermore, the associations were examined among subjects who were 40 to 79 years of age. However, these chronic diseases may have different etiology according to age, and these diseases are commonly observed among the elderly. Indeed, the possible benefits of green tea may be restricted to high intakes in high-risk populations 9, 16. Thus, it would be more appropriate to investigate the potential effects of green tea by targeting elderly people, who are expected to have consumed green tea for a longer period, since early childhood.
We therefore investigated the associations between green tea consumption and all-cause mortality and cancer, as well as CVD among the elderly in Shizuoka, which has the highest production of green tea leaves in Japan (17). Furthermore, we examined the effects of green tea consumption on specific cancer mortalities.
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Participants
Individual data were extracted from the participants of the Shizuoka Elderly Cohort Study, an ongoing population-based, prospective cohort study in Shizuoka prefecture, an industrialized urban area in Japan. Shizuoka prefecture is located almost in the center of Japan and has an area of 7,780 km2, a population of 3.8 million people, and 1.3 million households 18, 19. In December 1999, a total of 22,200 residents, who were stratified by both sex and age group (65 to 74; 75 to 84), were randomly
Results
The baseline characteristics of all the eligible subjects (N = 13,636) are shown according to the follow-up status in Table 1. The mean age of the participants was 74.3 years, 49.3% were women, and approximately 70% had never smoked. The proportions of subjects drinking less than one, one to three, four to six, and seven or more cups of green tea per day were 2.8%, 25.2%, 48.1%, and 23.9%, respectively. The deceased tended to be slightly older and were more likely to be men, smokers, and had
Discussion
The inverse associations between green tea and mortality were observed in an ongoing population-based, prospective cohort study among the elderly in Shizuoka prefecture, which has the highest production of green tea leaves in Japan (17). We found significant inverse associations between green tea consumption and mortality from all causes and CVD. Those who consumed seven or more cups per day, compared with those who consumed less than one cup per day, had a risk of all-cause and CVD mortality
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