Tea has long been believed to possess hypotensive effects in popular Chinese medicine, noted the researchers, but conflicting results have been shown among human trials and animal studies on the relation between tea consumption and blood pressure.
Epidemiological evidence about the long-term effect of tea on hypertensive risk is also inconsistent.
In the new study, the scientists from the National Cheng Kung University in Tainan, Taiwan examined the effect of tea drinking on the risk of newly diagnosed hypertension in 1507 subjects aged 20 or older, who did not have a hypertensive history when the study started.
Almost 40 per cent of the subjects were defined by the scientists as 'habitual' tea drinkers, meaning they consumed at least 120 millilitres of green tea or oolong tea everyday for at least one year.
The more tea people drank, the lower their risk of high blood pressure, write the authors in yesterday's Archives of Internal Medicine (164:1534-1540).
Compared with non-habitual tea drinkers, the risk of developing hypertension decreased by 46 per cent for those who drank 120-599 ml per day and was further reduced by 65 per cent for those who drank 600 ml daily or more.
The results were confirmed after adjusting for age, sex, socioeconomic status, family history of hypertension, body mass index, waist-hip ratio, lifestyle factors and dietary factors.
Tea is the second most consumed beverage in the world. Research has already found that it can lower cholesterol levels, protect against heart attacks and EGCG, one of the numerous catechins contained in green tea, is also being studied for its anti-cancer activity.
A recently published Japanese study found that black tea may be healthy for the heart through its action on blood vessels. The small study suggested that the drink dilates the vessels allowing faster blood flow.
Much of the research on tea is filtering through to consumers and in markets without traditional consumption of the most widely researched type - green tea - sales have boomed. According to a Datamonitor report in 2003, green tea consumption in the UK the previous year was more than 20 times the 1997 figure.