Black tea lowers BP

31 January 2012

MedWire News: Regular consumption of black tea significantly lowers systolic blood pressure (SBP) and diastolic BP (DBP), researchers have found.

Given the high prevalence of hypertension worldwide and the fact that it is a major risk factor for cardiovascular and total mortality, these findings have important public health importance, report Jonathan Hodgson (University of Western Australia, Perth) and colleagues in the Archives of Internal Medicine.

They conducted a randomized placebo-controlled double-blind trial of 95 regular tea drinkers aged 35–75 years with a body mass index of 19–35 kg/m² and a daytime ambulatory SBP of 115–150 mmHg at screening.

The participants were recruited from the general population. After randomization, they followed a low-flavenoid diet during a 4-week run-in period and throughout the 6-month intervention.

During the intervention phase, participants drank 3 cups per day of either 1493 g powdered black tea solids containing 429 mg polyphenols and 96 mg of caffeine (tea) or placebo matched on the basis of flavor and caffeine content, which contained no tea solids. They avoided drinking regular leaf tea during this time.

There were no significant differences at baseline with respect to mean age (56 years), body mass index (25 kg/m²⁾, and 24-hour SBP/DBP (121/72 mmHg) between the placebo and tea groups, respectively.

After regular ingestion of black tea over 6 months, however, the tea group had significantly lower SBP and DBP than the placebo group. Indeed, regular black tea consumption significantly reduced 24-hour ambulatory SBP by 2.7 mmHg at 3 months (p=0.006) and by 2.0 mmHg at 6 months (p=0.05), and DBP by 2.3 mmHg at 3 months (p<0.001) and by 2.1 mmHg at 6 months (p=0.003).

“At a population level, the observed differences in BP would be associated with a 10% reduction in the prevalence of hypertension and a 7% to 10% reduction in the risk of cardiovascular disease,” write Hodgson and team.

They note that the net effect of black tea consumption on overall 24-hour BP was mainly driven by daytime BP, which was reduced by 2.8 mmHg at 6 months (p<0.001).

“A large proportion of the general population have BP within the range included in this trial, making results of the trial applicable to individuals at increased risk for hypertension,” the authors explain.

They point out that the trial was generally underpowered to detect small but clinically important effects on BP, a major limitation.

“It is also possible that longer-term regular consumption of black tea is needed for significant falls in BP to become apparent.”

Hodgson and team add that a number of potential mechanisms exist to explain the effect of black tea on BP. “Hypertension and endothelial dysfunction are integrally related, and endothelial dysfunction may be an early marker for BP changes.

“Another possible mechanism involves effects of BP flavenoids to alter body weight and/or visceral fitness.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012

Arch Intern Med 2012; 172: 186–188