Two cups of black tea per day for eight days were associated with significant improvements in arterial stiffness, and decreases in systolic and diastolic blood pressure, report researchers from the University of L'Aquila in Italy and Unilever R&D in Vlaardingen, The Netherlands.
“We observed for the first time that black tea, naturally rich in flavonoids, counteracted or completely prevented the abnormalities in peripheral arterial hemodynamics that were caused by an acute oral fat load in never-treated hypertensive patients,” they wrote in Nutrients.
“It is important to note that while our study design was rigorous, it was also short-term and included a small number of subjects.
“A review of epidemiological and mechanistic studies suggests that flavonoids from different sources manifest beneficial effects on the cardiovascular system. Several lines of clinical and experimental evidence also indicate that tea may help to reduce cardiovascular disease risk by improving endothelial function and decreasing BP levels.
“This may significantly contribute to the cardiovascular disease incidence, when one considers that tea is globally the most consumed beverage after water.”
Interest in tea and its constituents has bloomed in recent years, with the greatest focus on the leaf’s polyphenol content. Green tea contains between 30 and 40% of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10%. Oolong tea is semi-fermented tea and is somewhere between green and black tea.
Most of the studies have focused on green tea and its constituents, most notably EGCG. Unilever, however, has focused a lot of R&D on the potential health benefits of L-theanine, an amino acid found in tea leaves that is thought to help reduce stress, promote relaxation and improve the quality of sleep, and theaflavins, which are compounds unique to black tea.
Led by Davide Grassi, the researchers recruited 19 people with elevated blood pressure to participate in their randomized, double-blind, controlled, cross-over study. Volunteers were randomly assigned to either consumer two cups of black tea per day (providing a flavonoid dose of 129 milligrams per cup) or placebo for eight days. The tea was consumed without sugar, milk, lemon or any other additives. They then underwent a 13 day washout period before crossing over to the other group.
Results showed that black tea was associated with reductions in the reflection index and stiffness index, both of which are measures of arterial health.
In addition, black tea was associated with 3.2 mmHg and 2.6 mmHg reductions in systolic and diastolic blood pressure, respectively. Black tea consumption also prevented increases in blood pressure after consuming a high fat meal, said Grassi and his co-workers.
“From a public health point of view, avoiding to suggest black tea consumption as a ticket to consume high-fat diets, these findings may be of relevance: the tested tea dose of 1 (acute) or 2 cups (per day) was moderate and the intervention time relatively short,” wrote the researchers. “Moreover, the average energy intake in this study of 824 kcal mimicked a serving size typical for the main meal in Western diets.”
2015, Volume 7, Number 2, Pages 1037-1051, doi:10.3390/nu7021037
“Black Tea Lowers Blood Pressure and Wave Reflections in Fasted and Postprandial Conditions in Hypertensive Patients: A Randomised Study”
Authors: D. Grassi, R. Draijer, G. Desideri, T. Mulder, C. Ferri