With blood pressure variation linked to cardiovascular disease, the results of the new study indicate that compounds found in black tea may offer heart health benefits.
“We have shown, for the first time to our knowledge, that the consumption of black tea can lower rates of systolic and diastolic blood pressure variation at nighttime,” wrote researchers in the American Journal of Clinical Nutrition.
“These effects were immediate and sustained during regular black tea consumption over 6 mo. The results show that simple dietary changes can influence BP variation, and a component of black tea solids, other than caffeine, is responsible.”
The study was performed by researchers from the University of Western Australia, Flinders University (Australia), Unilever Research and Development (Netherlands), the Russian Cardiology Research Center (Russia) and BakerIDI Heart and Diabetes Institute (Australia).
The study adds to the list of potential health benefits of tea and the compounds it contains.
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, and helping with weight management.
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 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea.
The researchers recruited 111 men and women with systolic blood pressure between 115 and 150 mmHg. The participants were randomly assigned to one of two groups: The first group consumed three cups per day of black tea, and the second group received the same number of cups of a flavonoid-free caffeine-matched beverage.
Results showed that after six months of consuming the beverages the tea group displayed “lower rates of systolic and diastolic blood pressure variation by about 10% during nighttime”, said the researchers.
Such effects were observed from the very first day of the study, they added, and maintained for the whole six month study.
Commenting on the potential mechanism, the researchers noted that “there is mounting evidence that black tea flavonoids can improve vascular health via effects on nitric oxide status, endothelial function, and arterial stiffness.
“Acute and short-term improvements in arterial stiffness may contribute to reduced blood pressure variation.
“An additional possibility is that tea might improve sleep quality via effects on neurocognitive function or autonomic regulation,” they added.
The study was funded by the National Health and Medical Research Council of Australia, and Unilever Research and Development..
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.112.051375
“Black tea lowers the rate of blood pressure variation: a randomized controlled trial”
Authors: J.M. Hodgson, K.D. Croft, R.J. Woodman, I.B. Puddey, D. Fuchs, R. Draijer, E. Lukoshkova, G.A. Head