The effects and bioactive reasoning of the substances in green tea on a person’s mental and physical health

Yuyei Wang, ywang29@student.kis.or.kr

Introduction

The concept of tea has been with us for around thousands of years. It is amazing to think that people from the past, who had much less technology than us, found out about tea and their functions. All of the numerous varieties of teas and their recognized beneficial effects are still being used in our society today. Green, black, white, oolong, pu-erh, chamomile, mint and rooibos tea are just a few out of what could be thousands of other kinds. Among the types of teas, green tea is well known and mostly consumed by many people. Something much more astonishing is that each and every substance in green tea gives off their very own special effect, ranging from reducing stress to helping you focus. But have you ever wondered what these effects are, or with how and why this happens?

Substances in Green Tea

There are three bioactive compounds found in green tea, which are  L-theanine, caffeine and EGCG. Of course, these aren’t the only substances found in green tea, as there are many more such as vitamins, minerals and pigments. However, the benefits that green tea is primarily known for comes from the combination of L-theanine, caffeine and EGCG. An amino acid found primarily in tea plants is called theanine. L-theanine, a type of theanine, is also a type of a non-protein amino acid found abundantly in tea leaves. EGCG, also known as epigallocatechin gallate, is a type of flavonoid(plant) compound.

L-theanine

In a 237ml cup of green tea, L-theanine usually takes up 20~60mg out of the entire cup, however, the amount can differ. L-theanine, a type of amino acid, is known to reduce stress and anxiety, especially in high-stress situations. This particular amino acid additionally promotes relaxation, supports focus and improves cognition along with protective effects on the brain. The mental processes that take place in the brain, including thinking, attention, language, learning, memory and perception are referred to as cognition. One evidence of these effects can be seen in Williams, Jackson L’s systematic review "The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review.", done in March of 2020, under the National Institutes of Health. This review analyzed 9 voluntary peers, who were supplemented 200~400mg a day, for its effects. The results showed lowered cortisol levels, decreased stress and improved mental calmness without causing any drowsiness. Despite the review concluding that L-theanine is a promising natural agent for stress and anxiety relief, more large scales of research may be needed. Additionally, it is to be kept in mind that green tea only contains roughly 10% of what those 9 voluntary peers consumed in a day. So, a person may not feel it to be as powerful as it is said to be when consuming green tea.

L-theanine works in a variety of ways to help our bodies relax. L-theanine primarily affects brain activity by increasing alpha brain waves, which represent a state of calm alertness. Alpha brain waves are brain waves with a frequency between 8–13 Hz that occur when a person is awake, relaxed, and alert, but not actively concentrating. L-theanine also calms neurotransmitters such as GABA, serotonin, and dopamine, which improves mood and reduces stress. An amino acid that serves as the primary inhibitory neurotransmitter in the brain is called GABA. Serotonin is a chemical that carries messages between nerve cells in the brain and the body. Dopamine is a neurotransmitter made in the brain that has a role to play in controlling memory, mood, sleep, learning, concentration, movement and other body functions. Regarding stress, L-theanine also helps lower cortisol levels, a hormone that is released when experiencing stress. This can guard a person's body against the detrimental effects of chronic stress. Furthermore, when paired with coffee, L-theanine can reduce nervousness and tension while increasing alertness and focus.

Caffeine

Caffeine, similar to L-theanine, is another substance that can be found in tea, according to "Effect of Green Tea Phytochemicals on Mood and Cognition" by Dietz & Dekker in 2017 under Current Pharmaceutical Design. In this case, pharmaceuticals are seen as any kind of drug used for medicinal purposes, while the phytochemical used in this study refers to a chemical produced by plants. A 237ml of green tea usually contains around 30~50mg of caffeine, although the amount may differ. Those who drink coffee are probably aware of the effects that caffeine holds. Caffeine can improve alertness, attention, reduce mental fatigue, and improve mental performance at times. However, unlike coffee, green tea contains a combination of L-theanine and caffeine. The combination of those two substances also combines the effects they have on a person’s body. An example of these effects can include increasing sustained attention, multitasking, mood balance and enhancing cognition while reducing overstimulation.

The principle of why caffeine causes your body to be much more alert and awake is much simpler than you expect it to be. Adenosine, a chemical in your brain, is what makes you sleepy along with reducing the alertness you feel. It also acts as a “central nervous system depressant” as Dr. Anya Mandal stated in News for Medical and Life Sciences on May 9th of 2025. Consuming caffeine blocks the effects of adenosine from reaching your brain. Because of this blockage, a person’s body will feel more alert and energetic than before.

EGCG

Unlike L-theanine and caffeine, EGCG takes up around 100–300mg per cup of green tea.  The amount of EGCG, just like every other ingredient, will also vary depending on the amount of green tea. While L-theanine and caffeine have effects on a person’s mental health, EGCG affects a person’s physical health. An article, “Beneficial Properties of Green Tea Catechins”, from National Library of Medicine and PubMedcentral that was published on March 4th of 2020, states that through research, EGCG has a potential of being anti-diabetic, anti to some cancers, anti-inflammatory, along with many other beneficial outcomes.

Despite being strongly against animal testing, an article stood out regarding more of EGCG’s abilities. From ScientificReport, “Epigallocatechin gallate (EGCG) alleviates vascular dysfunction in angiotensin II-infused hypertensive mice by modulating oxidative stress and eNOS”, published in 21 October 2022, EGCG is shown to have anti-hypertensive activity. In this scientific study, 8~10 week old hypertensive mice were given EGCG (50mg/kg per day) for 14 days. Their blood pressure was measured using a tail-cuff every three days. The vascular reactivity of these mice were measured using wire myographs, a type of gadget used to measure the force of a muscle under contraction. At the end the treatment with EGCG to these mice resulted in a lowered blood pressure, which was also partly attributed to the improvement in their vascular function. This means that EGCG has the power to lower high blood pressure. Being able to lower high blood pressure is a good thing because having high blood pressure ultimately puts strain on your blood vessels, heart, brain, kidneys, eyes and other organs, which can lead to serious damage.

EGCG works by increasing nitric oxide, a chemical that can enlarge blood vessels, to decrease blood pressure. By enlarging the blood vessels in your body, the pressure put on those vessels caused by the blood flow will lessen because there is more space. According to an experiment by Chatree S, Sitticharoon C, Maikaew P, “Epigollocatchin gallate decreases plasma triglyceride, blood pressure, and serum kisspeptin in obese human subjects”, 2021, decrease of blood pressure was measured after eight weeks of consuming 150mg of EGCG twice a day. EGCG is also shown to have the ability to hamper cancer’s development as it can prevent cells from dividing and multiplying. This helps the prevention of cancer because a cancers’ first development stage is when an uncontrolled cell divides too frequently.

Best Time to Consume Tea

As a short recap, green tea makes a person alert, improves mood, and reduces stress and anxiety, while also improving your physical health due to its bioactive compounds. One would gain the best benefits of the bioactive compounds in green tea by consuming them in situations that make them unfocused, stressed, anxious and unwell. This way, upon drinking green tea, the person will feel alert enough to properly do their work while also being less stressed about. As a cherry on top, the person will have better physical health along with their mental health.

Works Cited

1. How Green Tea Can Benefit Your Health, Cleveland Clinic, Sep 5, 2024.

2. Edele Mancini, Christoph Beglinger, Jurgen Drewe, Davide Zanchi, Undine E. Lang, Stefan Borgwardt, Green tea effects on cognition, mood and human brain function: A systematic review, Phytomedicine, Jul 21, 2017.

3. Yin-Ching Chan, Kazuaki Hosoda, Chin-Ju Tsai, Shingeru  Yamamoto, Ming-Fu Wang, Favorable Effects of Tea on Reducing the Cognitive Deficits and Brain Morphological Changes in Senescence-Acccelerated Mice, Nov 16, 2005

4. Christina Dietz, Matthijs Dekker, Effect of Green Tea Phytochemicals on Mood and Cognition, Bentham Science, 2017.

5. Elvira Gonzalez de Mejia, Marco Vinicio Ramirez-Mares, Sirima Puangpraphant, Bioactive components of tea: Cancer, inflammation and behavior, Elsevier, 2009.

6. Jackson L Williams, Julian M Everett, Nathan M D'Cunha, Domenico Sergi, Ekavi N Georgousopoulou, Richard J Keegan, Andrew J McKune, Duane D Mellor, Nicola Anstice, Nenad Naumovski, The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review, National Library of Medicine, Mar, 2020.

7. Ruxton, C. H. S, The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks, Nutrition bulletin, 2008.

Author Biography

Yuyei Wang is a freshman at Korea International School and has a deep interest in the field of biology, especially neuroscience, and chemistry. She wants to become an expert in neuroscience to help those whose lives are affected by neurological and brain function disorders. She also aims to unravel mysteries and complexities regarding neuroscience and the nervous system. In this paper, she researches the effects and bioactive reasoning of the substances in green tea on a person’s mental and physical health. Outside of her school, Yuyei is also studying and researching about the harmful changes on wildlife nervous systems caused by chemical waste with the goal of finding a way to reduce the damage. Through continuous studies and research throughout her high school years, she intends to expand her knowledge regarding the field of biology, especially neuroscience, and chemistry. Yuyei has great hopes for the potential advancement for neuroscience as it can give major positive impacts on one’s life.