Researchers at the University of Western Australia (UWA; Perth, Australia) conducted a randomized, placebo-controlled study involving 95 men and women who were regular tea drinkers. Participants had a mean body mass index (BMI) of 25 kg/m2 and a mean daytime ambulatory systolic blood pressure of 121 mm Hg at baseline. During a four-week run-in period, all of the participants consumed a low-flavonoid diet along with three cups of regular leaf tea per day. During the six-month intervention period, the participants were randomized to three cups per day of either 1,493-mg powdered black tea solids that contained 429 mg of polyphenols and 96 mg of caffeine, or a placebo drink matched in flavor and caffeine content.

The results showed that drinking three cups each day for six months lowered both diastolic and systolic BP. For systolic readings, BP was lower by 2.7 mm Hg at three months and 2.0 mm Hg lower at six months in the participants who were drinking tea. For diastolic BP, the differences were 2.3 and 2.1 mm, respectively. According to the researchers, even these small changes could have a large impact on health at a population level, resulting in a possible 10% reduction in the prevalence of hypertension and a 7%-10% decrease in the risk of cardiovascular disease (CVD). The study was published on January 23, 2011, in Archives of Internal Medicine.

“Endothelial dysfunction may be an early marker for changes in blood pressure, and there is evidence that tea consumption improves endothelial function,” concluded lead author Jonathan Hodgson, PhD, and colleagues. “Tea flavonoids affect nitric oxide status and reduce levels of endothelin; this could contribute to reduced vascular tone and lower blood pressure. Another possible mechanism involves the effects of tea flavonoids on body weight and visceral fatness.”

Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water; the term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world worldwide and is usually the major source of flavonoids, often providing more than half of total intake. There are at least six different types of tea: white, yellow, green, oolong, black, and postfermented teas. A tea's type is determined by the processing which it undergoes; black tea is wilted, sometimes crushed, and is fully oxidized. The halting of oxidization is done by heating, and is carried out simultaneously with the drying.

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