- Drinking tea is associated with a variety of health benefits, including lowering blood pressure.
- Researchers have discovered how compounds called catechins, found in green and black tea, relax the smooth muscle that runs through blood vessels, which can lead to lower blood pressure.
- The discovery could lead to the development of better medicines for high blood pressure, also called hypertension.
- The finding may also inspire new treatments for an debilitating condition called epileptic encephalopathy.
People first drank caffeinated tea in China more than 4,000 years ago. Since then, it has become one of the most popular drinks worldwide, the second next to water.
Both green and black tea are brewed from the leaves of the same shrub, Camellia sinensis, but green tea, which is made from unfermented leaves, contains more antioxidants.
Oxidation during the fermentation process of black tea reduces its antioxidant levels.
Several studies have found that green tea inhibits the formation of cancer, lowers high blood pressure and reduces the risk of heart disease.
However, the molecular mechanism responsible for the effect on blood pressure has so far been unclear.
Scientists at the University of California, Irvine (UCI) and the University of Copenhagen, in Denmark, have found that antioxidants in tea can open channels and relax the muscles that lead through the blood vessels.
They report their findings in the journal Cellular physiology and biochemistry.
The discovery could lead to the design of more effective anti-hypertensive drugs, which could potentially improve the health of millions of people around the world.
According to the National Heart, Lung, and Blood Institute, high blood pressure control or lowering can help prevent chronic kidney disease, heart attacks, heart failure and possibly dementia.
The Centers for Disease Control and Prevention (CDC) reports that nearly half of all adults in the United States have hypertension. It is estimated that the situation in 2018 played a role in the deaths of nearly half a million people in the country.
The World Health Organization (WHO), meanwhile, estimates that more than 1 billion people worldwide have hypertension.
The new study first shows that two antioxidants in tea, known as catechins, open a protein channel in the membranes of the smooth muscle cells that line the blood vessels. This allows positively charged potassium ions to leave the cells.
Channels in nerve and muscle cells maintain tension across their membranes by letting in and out of negative and positive ions in a controlled manner. They are ‘stressful’, meaning they respond to changes in this stress by opening or closing.
The researchers found that the catechins in green tea activate a specific type of potassium ion channel called KCNQ5.
Previous work by some of the same scientists suggests that this protein channel may underlie the antihypertensive effects of several plants used as medicines for millennia.
For the new study, the researchers used computer modeling and mutated versions of the channel protein to show that the two catechins bind to a portion that changes voltage.
“With this binding, the channel can open much easier and earlier in the process of cellular excitation,” explains senior author, prof. Geoffrey Abbott, from the Department of Physiology and Biophysics at the UCI School of Medicine.
In theory, it should make the muscle cells less “excited” and therefore less likely to contract. Rather, they should relax, dilate the blood vessel and lower blood pressure.
To test this theory, prof. Abbott’s co-authors at the University of Copenhagen measured changes in tension in the walls of arteries of rats. Their findings confirmed that the two catechins relax from tea and dilate arteries by activating the KCNQ5 ion channel.
The authors are confident that the addition of a splash of milk to black tea does not reduce the anti-hypertensive effects.
Milk tea, applied directly to cells in the laboratory, could not activate their KCNQ5 channels. But this is probably not the case when someone drinks it.
Prof. Abbott explains:
“We do not believe this means that you should 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 them. [the] catechins’ beneficial effects. ”
The scientists also discovered that heating green tea to 35 ° C increases the activation of KCNQ5.
Lovers of iced tea, however, need not worry.
“Regardless of whether tea becomes icy or hot, this temperature is reached after the tea has been drunk, because the human body temperature is about 37 ° C,” says prof. Abbott. “So, simply by drinking tea, we activate its beneficial, anti-hypertensive properties.”
KCNQ5 also exists in the nerve membranes in the brain, where it helps regulate electrical activity and signal transmission.
People with a disorder called epileptic encephalopathy have a version of the channel protein that does not respond effectively to stress changes, leading to frequent seizures.
The authors of the study pointed out that catechins can cross the blood-brain barrier, preventing larger molecules, including some drugs, from entering the brain.
In theory, therefore, drugs based on catechin molecules may help to correct the cause of epileptic encephalopathy.
“The discovery of their ability to activate KCNQ5 may suggest a future mechanism to resolve broken KCNQ5 channels to ameliorate brain arousal disorders due to their dysfunction,” the researchers conclude.
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