- Drinking tea is associated with a number of health benefits, including lowering blood pressure.
- The researchers found how compounds called catechins, found in green and black teas, relax the smooth muscle that lines blood vessels, which can lead to lower blood pressure.
- The discovery could lead to the development of better drugs for hypertension, also called hypertension.
- The discovery may also inspire new treatments for a debilitating condition called epileptic encephalopathy.
Humans drank caffeinated tea for the first time more than 4,000 years ago in China. Since then, it has become one of the most popular drinks in the world, second only to water.
Green and black teas are produced from the leaves of the same bush, Camellia sinensis, but green tea, which is made from unfermented leaves, contains more antioxidants.
Oxidation during the fermentation process of black tea reduces its levels of antioxidants.
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 is unclear so far.
Scientists at the University of California, Irvine (UCI) and the University of Copenhagen, Denmark, have found that tea’s antioxidants open ion channels and can relax the muscles that line blood vessels.
They report their findings in the newspaper Cell Physiology and Biochemistry.
The discovery may guide the development of more effective antihypertensive drugs, which can improve the health of millions of people worldwide.
According to the National Heart, Lung and Blood Institute, controlling or reducing high blood pressure can help prevent chronic kidney disease, heart attacks, heart failure and possibly dementia.
The Centers for Disease Control and Prevention (CDC) report that almost half of all adults in the United States have hypertension. He estimates that, in 2018, the condition influenced the death of almost half a million people in the country.
The World Health Organization (WHO), in turn, estimates that more than 1 billion people worldwide have hypertension.
The new study shows for the first time that two antioxidants in tea, known as catechins, open a protein channel in the membranes of smooth muscle cells that line blood vessels. This allows positively charged potassium ions to leave the cells.
The channels in nerve and muscle cells maintain tension across their membranes, allowing negative and positive ions to pass in and out in a controlled manner. They are “voltage controlled”, which means that they respond to changes in this voltage by opening or closing.
The researchers found that 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 various plants used as folk remedies for millennia.
For the new study, the researchers used computer models and mutated versions of the channel protein to show that the two catechins bind to a section that detects voltage changes.
“This connection allows the channel to open much more easily and earlier in the process of cellular excitation”, explains the study’s senior author, Prof. Geoffrey Abbott, from the Department of Physiology and Biophysics at the UCI School of Medicine.
In theory, this should make muscle cells less “excitable” and therefore less likely to contract. Instead, they should relax, dilating the blood vessel and lowering blood pressure.
To test this theory, the co-authors of Prof. Abbott at the University of Copenhagen measured changes in tension in the walls of rat arteries. Their findings confirmed that the two catechins in tea relax and dilate the arteries, activating the KCNQ5 ion channel.
The authors are confident that adding a little milk to black tea does not reduce its antihypertensive effects.
Milk tea, applied directly to cells in the laboratory, failed to activate its KCNQ5 channels. But it is probably not the case when a person drinks.
Prof. Abbott explains:
“We do not believe that this means avoiding 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 catechins from proteins and other milk molecules that would otherwise block [the] beneficial effects of catechins. “
Scientists also found that heating green tea to 35 ° C increased KCNQ5 activation.
However, lovers of iced tea need not worry.
“Regardless of whether tea is consumed cold or hot, this temperature is reached after ingesting the tea, as the human body temperature is around 37 ° C”, says Prof. Abbott. “Thus, simply by drinking tea, we activate its beneficial and antihypertensive properties.”
KCNQ5 also exists in the nerve membranes of the brain, where it helps to 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 voltage changes, which leads to frequent seizures.
The study authors point out that catechins can cross the blood-brain barrier, which prevents larger molecules, including some drugs, from entering the brain.
In theory, drugs modeled on catechin molecules could therefore help to correct the cause of epileptic encephalopathy.
“The discovery of its ability to activate KCNQ5 may suggest a future mechanism for repairing broken KCNQ5 channels to improve brain excitability disorders resulting from its dysfunction,” conclude the researchers.
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