Tea’s Janus Effect Upon the Brain

How can tea wake us up and calm us down?

Posted Mar 12, 2011

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 the brain. 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. 

Alcohol enhances the action of GABA in our brain while theanine is converted into GABA within our brain after we drink tea. This is why consuming high doses of theanine can enhance the effects of alcohol - they synergize with each other!  Thus, tea can both energize our minds via its caffeine and relax our minds via the actions of theanine.  Tea, like so many other plants we consume (see my blogs on marijuana for comparison), contains a complex mixture of chemicals that are potentially psychoactive, or, as is the case with theanine (and marijuana), are converted in our bodies into a psychoactive substance.  Tea is not unique in having chemicals that produce both activation and inhibition in the brain; this property is actually quite common in nature, for example the hallucinogenic mushroom Amanita muscaria contains both ibotenic acid (a stimulant) and muscimol (a depressant).

Should you be concerned? Not at all. The concentration of theanine in tea is quite safe even if you plan on having multiple cups throughout the day.  Even extremely high doses of theanine do not appear to be harmful - at least to laboratory rats.

© Gary L.Wenk, Ph.D., author of Your Brain on Food (Oxford, 2010)

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