30 April 2021

Tea and Blood Pressure

Welcome back. Come in; please sit down. Would you care for a cup of tea? began a blog post seven years ago. After blogging about the virtues of coffee (Caffeine, Health and Memory), I paid homage to tea (Tea Time). As I wrote at the time, I started drinking green tea with a little milk before exercising because it was way too early in the morning to caffeinate with coffee.

Serving tea (photo from multiple websites).

The research findings on tea’s health benefits were generally positive; unlike coffee, it was hard to find any negatives. Observational studies had found reduced risk of cardiovascular disease and stroke, slightly lower blood pressure and LDL (bad) cholesterol as well as other improvements, such as inhibited blood clotting. The only problem I had was that some research suggested milk negated tea’s health benefits.

Seven years have passed, and a recent study has got me focusing on hypertension (high blood pressure) and tea’s antihypertensive (blood pressure lowering) properties.

The U.S. National Health, Lung and Blood Institute of the National Institutes of Health describes hypertension as a common disease that develops when blood flows through your arteries at higher-than-normal pressures. Controlling or lowering blood pressure can help prevent or delay chronic kidney disease, heart attack, heart failure, stroke and possibly vascular dementia.

Blood pressure guidelines adopted in 2017 by American Heart Association, American College of Cardiology and nine other health organizations (from www.health.harvard.edu/heart-health/reading-the-new-blood-pressure-guidelines).

The study by researchers affiliated with the University of California, Irvine, and Denmark’s University of Copenhagen determined that certain compounds in tea relax the muscle that lines blood vessels and may be responsible for lowering blood pressure.

Here’s the thing. While drinking tea may not produce a major reduction in blood pressure, their finding could point the way to the development of new, more effective blood pressure-lowering medications. That would be a very big deal. Consider the numbers. In 2019, the World Health Organization estimated that, worldwide, 1.13 billion people have hypertension. In 2018, the Centers for Disease Control and Prevention (CDC) judged that hypertension was a primary or contributing cause of nearly half a million deaths in the U.S.

Breaking Down the Results
The study details are steeped in vascular biology, biophysics and bioelectricity, but I’ll take a swipe if you’ll bear with me. I’ll start with an excerpt from my Tea Time blog post: tea is loaded with polyphenols, particularly flavonoids such as catechins, which have antioxidant and other potentially useful properties and different effects on the body.

Channels in nerve and muscle cells maintain voltages across their membranes by allowing controlled passage of positive and negative ions. They are voltage-gated, responding to voltage changes by opening or closing.

The researchers showed that two tea catechins each activate a specific type of ion channel protein labeled KCNQ5, which allows potassium ions to diffuse out of cells to reduce cellular excitability. KCNQ5 is found in the smooth muscle that lines blood vessels. The researchers predicted then confirmed that its activation by tea catechins would relax blood vessels.

Wrap Up
What about adding milk to tea? The researchers added tea with milk directly to cells, and it did indeed fail to activate the cells’ KCNQ5 channels. They are confident, however, that drinking tea with milk, whether hot or iced, would have different results. The stomach’s warm environment should separate the catechins from the proteins and other molecules in milk that would block the catechins’ beneficial effects.

Who am I to argue? So, enjoy your black, green, oolong or white tea, straight or with milk. 

Enjoy your tea with or without milk, and if no one is looking, have fun (photo from multiple websites).
Oh, herbal teas, such as hibiscus and chamomile, may offer antioxidants and health benefits, yet they are not true teas from the Camellia sinensis plant species. They lack flavonoids and were not addressed by the study.

Thanks for stopping by.

Study of KCNQ5 activation by tea in Cellular Physiology and Biochemistry journal:  www.cellphysiolbiochem.com/Articles/000337/
Articles on study on EurekAlert! and MedicalNewsToday websites:

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