Tea’s Janus Effect Upon the Brain

Reading the article it struck me this peculiar English habit of offering a cup of tea when things go really bad. It seems that they have a reason, and a scientific one too!

A post from Psycology today by Professor Gary L. Wenk, Ph. D. has the whole story. Here is a part:

Credit: http://tea-brewery.com/

Without doubt, drinking tea is good for our general health.  Much has already been written about the benefits of its principle psychoactive stimulant, caffeine, on mental function, alertness and attention. There are many popular beverages containing extracts from tea leaves that are marketed with claims that these drinks will help you to focus or concentrate better.  Paradoxically, other beverages containing identical tea extracts claim that they have relaxing and tranquillizing properties.  This seems contradictory.  How is it possible that drinking tea can stimulate the mind, improve focus and provide mental energy and simultaneously induce relaxation and calm?  

The answer is due to the presence of the chemical theanine that is found in tea. The combined actions of theanine and caffeine are responsible for the complex and pleasant effects of tea upon thebrain. Caffeine, as all coffee drinkers are well aware, is a mental stimulant.  Theanine is the anti-stimulant. Theanine looks very much like a brain chemical called glutamate.  Glutamate produces excitation and is responsible for allowing us to form new memories; glutamate is also responsible for the death of neurons associated with many diseases of aging, such as Alzheimer's disease and ALS.  However, theanine performs a chemical trick that glutamate cannot achieve; theanine can cross the blood-brain barrier and therefore has access to the brain from our intestines after we enjoy a nice cup of tea. Once theanine has entered the brain it then displays yet another peculiar property.  Although theanine looks like glutamate it is not able to mimic the actions of glutamate at all.  Instead, it is consumed by cells called astrocytes and converted into a chemical called GABA.  What is GABA?  

GABA provides inhibition in the brain - it turns us off.  When we release too much GABA in our brain we become drowsy.  This probably explains why recent studies have shown that tea drinking slows down the speed of our brain waves.  When we have a lot of GABA floating around in our brain we fall asleep. So what happens if you consume too many beverages containing theanine?  When people were given high doses of theanine they had difficulty performing complex motor tasks such as driving or speaking.  In addition, high doses of theanine actually enhanced the sedating actions of alcohol. This last finding may actually help to explain how theanine in our cup of tea is able to relax us.