A prospective cohort study of more than 40,000 people in Japan has shown that drinking green tea can significantly cut deaths from cardiovascular disease (CVD) as well as all-cause mortality, particularly in women. Shinichi Kuriyama, MD, from Tohuku University Graduate School of Medicine in Miyagi, Japan, told Diabetes in Control, "I think our study provides strong evidence regarding the benefits of drinking green tea in humans on CVD, but not cancer, with a large sample size."
"The reason for the discrepancy between effects on CVD and on cancer deaths in our study is uncertain. Substantial evidence from in vitro and animal studies indicates that green tea preparations can inhibit both CVD and carcinogenic processes.
owever, recent epidemiological studies have indicated that green tea consumption is associated with reduced cardiovascular risk profiles but have demonstrated almost null data regarding the association between green tea consumption and cancer at various sites. Our results are almost consistent with those of the recent epidemiologic studies."
Dr. Kuriyama and colleagues explain that almost all Japanese people consume green tea as one of their favorite beverages. They designed their prospective analysis to examine the association between green tea consumption and mortality due to all causes, CVD, and cancer within a large population-based cohort study of 40,530 people in Miyagi Prefecture in northeastern Japan.
For 11 years (follow-up rate for all-cause mortality, 86.1%), 4209 participants died, and for up to 7 years, (follow-up rate for cause-specific mortality, 89.6%), 829 people died of CVD, and 1134 died of cancer.
Compared with participants who drank less than 1 cup of green tea per day, those who consumed 5 or more cups had a risk for all-cause and CVD mortality that was 16% lower (during 11 years of follow-up) and 26% lower (during 7 years of follow-up), respectively.
The inverse association with CVD mortality was stronger than that with all-cause mortality, and among the types of CVD, the strongest inverse association was seen for stroke mortality.
The inverse association between green tea consumption, CVD, and all-cause mortality was stronger in women than in men (P = .08 for interaction with sex). In women, the multivariate hazard ratios of CVD mortality across increasing green tea consumption categories (cups/day) were 1.00, 0.84, 0.69, and 0.69, respectively (P = .004 for trend).
"The reason for the discrepancy between men and women for the association of green tea consumption and risk of all-cause and CVD mortality is uncertain," say the researchers.
The authors add that the effect of green tea "appears to be a threshold effect rather than a dose-response relationship, such that persons who consume at least 1 cup a day may receive some benefit."
A number of biological mechanisms, including radical scavenging and antioxidant properties, have been proposed for the beneficial effects of green tea. The authors note that previous studies have suggested that green tea favorably affects hypertension, low-density lipoprotein cholesterol levels, and atherosclerosis.
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