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- Drinking tea is associated with a range of health benefits, including reduced blood pressure.
- Researchers have found how compounds called catechins, found in green and black teas, relax the smooth muscle that lines blood vessels, which can lead to low blood pressure.
- The discovery could lead to the development of better drugs for high blood pressure, also known as hypertension.
- The discovery could also inspire new treatments for a debilitating disease called epileptic encephalopathy.
Humans first drank caffeinated tea over 4,000 years ago in China. Since then, it has become one of the most popular drinks in the world, just behind water.
Green and black teas are brewed from the leaves of the same shrub, Camellia sinensis, but green tea, made from unfermented leaves, contains more antioxidants.
Oxidation during the fermentation process of black tea lowers its levels of antioxidants.
Several studies have shown that green tea inhibits the formation of cancers, lowers high blood pressure and reduces the risk of heart disease.
However, the molecular mechanism responsible for the effect on blood pressure has not been clear until now.
Scientists at the University of California at Irvine (UCI) and the University of Copenhagen, Denmark, have found that the antioxidants in tea open ion channels and can relax the muscles that line blood vessels.
They report their findings in the newspaper Cell physiology and biochemistry.
This discovery could guide the design of more effective antihypertensive drugs that can improve the health of millions of people around the world.
According to the National Heart, Lung, and Blood Institute, controlling or lowering high blood pressure 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 high blood pressure. He estimates that in 2018, the disease 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 a billion people worldwide suffer from hypertension.
The new study first shows that two antioxidants in tea, called catechins, open a protein channel in the membranes of smooth muscle cells that line blood vessels. This allows the positively charged potassium ions to leave the cells.
Nerve and muscle cell channels maintain tension across their membranes by allowing negative and positive ions to enter and exit in a controlled manner. They are “voltage-dependent”, which means that they respond to changes in this voltage by opening or closing.
Researchers have found that catechins in green tea activate a special 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 herbs that have been used as traditional 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 section that detects changes in voltage.
“This binding allows the channel to open much more easily and earlier in the process of cellular arousal,” says lead author of the study, Professor Geoffrey Abbott, of the School’s Department of Physiology and Biophysics. of UCI Medicine.
In theory, this should make the muscle cells less “excitable” and therefore less likely to contract. Rather, they should relax, dilate the blood vessel, and lower blood pressure.
To test this theory, the co-authors of Professor Abbott at the University of Copenhagen measured the voltage changes in the artery walls of rats. Their findings confirmed that the two catechins in tea relax and dilate arteries by activating the KCNQ5 ion channel.
The authors are convinced that adding a pinch of milk to black tea does not reduce its antihypertensive effects.
Milk tea, applied directly to the cells in the lab, failed to activate their KCNQ5 channels. But that’s probably not the case when a person drinks it.
Professor Abbott explains:
“We don’t think this means avoiding milk while drinking tea to experience the beneficial properties of tea. We are confident that the environment of the human stomach will separate catechins from proteins and other molecules in milk that would otherwise block [the] the beneficial effects of catechins. “
Scientists also found that warming green tea to 35 ° C increased activation of KCNQ5.
However, iced tea lovers need not worry.
“Whether the tea is consumed iced or hot, this temperature is reached after the tea is consumed because the human body temperature is around 37 ° C,” says Professor Abbott. “So, just by drinking tea, we activate its beneficial antihypertensive properties.”
KCNQ5 also exists in the membranes of the nerves of 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 doesn’t respond effectively to changes in blood pressure, which leads to frequent seizures.
The study’s 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 correct the cause of epileptic encephalopathy.
“The discovery of their ability to activate KCNQ5 may suggest a future mechanism to repair broken KCNQ5 channels to improve brain excitability disorders resulting from their dysfunction,” the researchers conclude.
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