The specific biological properties of green tea and the health benefits of its consumption have been postulated from epidemiological, basic and clinical investigations. In particular, numerous studies have shown the potential preventive and therapeutic effects of green tea on cardiovascular diseases and cancer in certain populations whose lifestyle involves high green tea consumption. A recent study by Suzuki and colleagues has reported on green tea consumption and mortality among elderly people in Japan .
13,636 tea drinkers who were stratified by both sex and age group (65–84 years) filled questionnaires in 1999, 2002 and 2006. On each occasion, the subjects were classified into those who were still alive and who returned the questionnaire, those who had died and their date of death, and those who were still alive but did not return the questionnaire. Since some were lost to follow-up, data from a total of 12,251 subjects were analyzed.
In the self-administered questionnaires, in addition to major basic characteristics, data requested included the frequency of green tea consumption per day during the past month, smoking and drinking habits, past history of illness including stroke, cancer, heart disease, hypertension and diabetes. Identification of the causes of death of the deceased subjects was accomplished by record linkage of the cohort database with the National Vital Statistics Database from the Ministry of Health, Labor and Welfare of Japan.
Based on the frequency of daily green tea consumption, the subjects were divided into four groups, namely, those who drank < 1 cup per day, 1–3, 4–6 and ≥ 7 cups per day (the volume of 1 cup = 60–90 ml).
The mean age was 74.3 years. Less than 1 cup/day of green tea was consumed by 2.8%, 1–3 cups by 5.2%, 4–6 cups by 48.1% and ≥ 7 cups by 23.9%. The majority of subjects who consumed < 1 cup/day were males, smokers and showed a sedentary lifestyle. The follow-up rate for > 6 years was 71.6%, and the mean follow-up period was 5.2 years.
All-cause mortalities for the groups drinking < 1 cup/day and ≥ 7 cups/day were 42.3 deaths/1000 person-years (95% CI 32.4–54.3) and 14.4 deaths/1000 person-years (95% CI 12.6–16.4), respectively. The mortalities from cardiovascular disease (CVD) of these two groups were 17.1 deaths/1000 person-years (95% CI 11.0–25.2) and 3.2 deaths/1000 person-years (95% CI 2.4–4.2), respectively. The results indicated that green tea consumption and mortality from all causes, CVD and colorectal cancer were inversely associated, whereas green tea consumption and mortality from other cancers were not inversely associated.
The authors concluded that this study provided more evidence of the protective effects of green tea on all-cause and CVD mortality of elderly residents who consumed green tea frequently. Although there was no clear pattern of an inverse association between gastric and lung cancer mortality, the protective effect of green tea against colorectal cancer was suggested. Thus, high cumulative exposure to green tea may produce significant preventive benefits for public health.
Professor Emeritus, Tokyo Medical and Dental University, Japan
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