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Drinking green and black tea does lower blood pressure

So get your daily cuppa, and even though it might be better if you don't add milk, researchers say it may not make that much difference if you do

Flavonoids in tea are responsible for the blod-pressure lowering properties of tea
Flavonoids in tea are responsible for the blod-pressure lowering properties of tea (Verena Böttcher/Unsplash)

A new study from the University of California, Irvine shows that compounds in both green and black tea relax blood vessels by activating ion channel proteins in the blood vessel wall. The discovery helps explain the antihypertensive properties of tea and could lead to the design of new blood pressure-lowering medications.

Published in Cellular Physiology and Biochemistry, the discovery was made by the laboratory of Geoffrey Abbott, PhD, a professor in the Department of Physiology and Biophysics at the UCI School of Medicine.

Results from the research revealed that two catechin-type flavonoid compounds (catechins are a type of natural phenol and antioxidant) found in tea, each activate a specific type of ion channel protein named KCNQ5, which allows potassium ions to diffuse out of cells to reduce cellular excitability. As KCNQ5 is found in the smooth muscle that lines blood vessels, its activation by tea catechins was also predicted to relax blood vessels, thus lower blood pressure.

While prior studies demonstrated that consumption of green or black tea can reduce blood pressure by a small but consistent amount, the identification of KCNQ5 as a novel target for the hypertensive properties of tea catechins may facilitate the creation of new drugs or dietary methods to control hypertension.

Tea has been produced and consumed for more than 4,000 years and upwards of 2 billion cups of tea are currently drunk each day worldwide, second only to water in terms of the volume consumed by people globally. The three commonly consumed caffeinated teas (green, oolong, and black) are all produced from the leaves of the evergreen species Camellia sinensis, the differences arising from different degrees of fermentation during tea production.

Black tea is commonly mixed with milk before it is consumed in many countries. The researchers in the present study found that when black tea was directly applied to cells containing the KCNQ5 channel, the addition of milk prevented the beneficial KCNQ5-activating effects of tea. However, according to Abbott, “We don’t believe this means one needs to avoid milk when drinking tea to take advantage of the beneficial properties of tea. We are confident that the environment in the human stomach will separate the catechins from the proteins and other molecules in milk that would otherwise block catechins’ beneficial effects.”

This hypothesis is borne out by other studies showing antihypertensive benefits of tea regardless of whether it is consumed along with milk. The team also found, using mass spectrometry, that warming green tea to 35 degrees Celsius alters its chemical composition in a way that renders it more effective at activating KCNQ5.

“Regardless of whether tea is consumed iced or hot, this temperature is achieved after tea is drunk, as human body temperature is about 37 degrees Celsius,” explained Abbott. “Thus, simply by drinking tea we activate its beneficial, antihypertensive properties.”

Source: UCI School of Medicine

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