A study published in Cellular Physiology & Biochemistry, a journal our of the University of California, Irvine, has shown that compounds in both green and black tea relax blood vessels by activating ion channel proteins in the blood vessel wall. The authors note that this discovery helps explain the antihypertensive properties of tea and could ultimately lead to the design of new blood pressure-lowering medications.
The research found that two catechin-type flavonoid compounds (epicatechin gallate and epigallocatechin-3-gallate) 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.
Prior studies have demonstrated that consuming green or black tea can reduce blood pressure by a small but consistent amount, and catechins are known to contribute to this property. But this study's identification of KCNQ5 as the mechanism of action may facilitate medicinal chemistry optimization for improved potency or efficacy.
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, and the researchers 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 the tea. 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," offered Geoffrey Abbott, PhD, professor in the Department of Physiology and Biophysics at the UCI School of Medicine. "Thus, simply by drinking tea we activate its beneficial, antihypertensive properties."