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Green tea is associated with reduced mortality

Can green tea consumption reduce the risk of premature mortality?

Can green tea consumption reduce the risk of premature mortality?

Synopsis

The authors of this study analysed data from a large population-based cohort of 40,530 people living in north-eastern Japan, where green tea is widely consumed.

Beginning in 1994, healthy adults aged 40 to 79 received a questionnaire inquiring about the frequency of intake of four drinks (green tea, black tea, oolong tea and coffee) and 36 food items.

Individuals reported green tea consumption in five categories: never, occasionally, one to two cups per day, three to four cups per day, and five or more cups per day. Validation with daily food diaries occurred randomly for 113 participants.

Researchers investigated causes of death by reviewing public records, but the authors do not state whether blinding to green tea consumption occurred.

Follow-up occurred for up to 11 years for all-cause mortality for 86 per cent of participants and for up to seven years for cause-specific mortality for 90 per cent of participants.

Statistical analysis controlled for potential confounding variables, including: age; job status; body mass index; exercise; history of hypertension, diabetes, or gastric ulcer; smoking; alcohol consumption; and other food consumption.

Green tea consumption was significantly associated with reduced cardiovascular and all-cause mortality. Drinking more than one cup per day was associated with reduced mortality in women; however, drinking less than five cups per day of green tea was not associated with reduced mortality in men.

Consuming green tea was not associated with a significant reduction in cancer mortality. Interestingly, the inverse relationship between green tea consumption and cardiovascular mortality was significant only in participants who never smoked.

The authors report that the consumption of black tea or oolong tea was not associated with reduced mortality, but do not comment on the relationship between coffee and mortality.

Level of evidence

2b (see www.infopoems.com/concept/ ebm_loe.cfm)

Reference

Kuriyama S et al. Green tea consumption and mortality due to cardiovascular disease, cancer and all causes in Japan: the Ohsaki study. JAMA 2006;296:1255-1265.

Bottom line: Green tea consumption is associated with reduced cardiovascular and all-cause mortality, but not cancer mortality.

Women appear to benefit more than men: men's mortality was significantly reduced only in those consuming more than five cups per day.

Furthermore, there appears to be no benefit of green tea consumption in smokers.

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