1 comment(s)
Drinking three cups each day for six months lowered both diastolic and systolic blood pressure by 2 to 3 mm Hg (P≤0.05), according to Jonathan Hodgson, PhD, of the University of Western Australia in Perth, and colleagues.
Even those small changes could have a large impact on health at the population level, they reported in a research letter in Archives of Internal Medicine.
Those differences would be associated with a 10% reduction in the prevalence of hypertension and a 7% to 10% decrease in the risk of cardiovascular disease, they said.
Hodgson and colleagues conducted a randomized trial that included 95 men and women ages 35 to 75 (mean age 56 for men and 57 for women) who were regular tea drinkers. The participants had a mean body mass index 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.
From baseline to six months, there were no changes in energy and nutrient intake, urinary sodium and potassium excretion, or body weight in either group.
There were, however, differences in 24-hour ambulatory blood pressure, driven mostly by daytime readings.
For systolic, readings were 2.7 mm Hg lower at three months and 2.0 mm Hg lower at six months in the participants who were drinking tea.
For diastolic, the differences were 2.3 and 2.1 mm Hg, respectively.
Hodgson and colleagues noted that previous short-term randomized trials exploring the effects of black tea on blood pressure may have failed to demonstrate significant effects because they were underpowered to find small but clinically significant differences.
It is also possible, they noted, that longer-term consumption is needed to make an impact.
As for why black tea would lower blood pressure, the researchers pointed to effects on endothelial function.
Endothelial dysfunction may be an early marker for changes in blood pressure, and there is evidence that tea consumption improves endothelial function. Also, a previous study by Hodgson and colleagues showed that tea flavonoids affect nitric oxide status and reduce levels of endothelin.
"This could contribute to reduced vascular tone and lower blood pressure," the authors wrote.
Another possible mechanism involves the effects of tea flavonoids on body weight and visceral fatness.
"A recent meta-analysis suggests that green tea and its flavonoids -- many of which are structurally similar to black tea flavonoids -- together with caffeine can reduce body weight and abdominal fatness," wrote the researchers, who noted that, although there was no change in body weight in the current study, information on abdominal fatness was not available.
Funding
for the study was provided by the National Health and Medical Research
Council of Australia and Unilever Research and Development in
Vlaardingen, the Netherlands.
The authors reported that they had no conflicts of interest.
The authors reported that they had no conflicts of interest.
Primary source: Archives of Internal Medicine
Source reference:
Hodgson J, et al "Effects of black tea on blood pressure: A randomized controlled trial" Arch Intern Med 2012; 172: 186-188.
Source reference:
Hodgson J, et al "Effects of black tea on blood pressure: A randomized controlled trial" Arch Intern Med 2012; 172: 186-188.
No comments:
Post a Comment