Green tea is well known for its high amounts of antioxidants, particularly one known as epigallocatechin gallate or EGCG. However, green tea also contains a high amount of an amino acid known as L-theanine.
L-theanine is widely used and studied in Japan, a culture particularly known for their tea consumption.
L-theanine has been observed to promote relaxation and reduce stress by a variety of possible mechanisms, with clinical evidence also showing these benefits.
Studies have shown that L-theanine increases alpha-wave activity in the brain, as well as the levels of serotonin, dopamine and GABA. L-theanine has been shown to be neuroprotective, in part by having an antagonistic effect on glutamate subtype AMPA receptors also increasing glutathione as well as its related antioxidant enzymes (superoxide dismutase and catalase) under stressful settings. It also supports nerve growth and new pathways via increasing levels of brain-derived neurotrophic factor (BDNF).
Clinically, supplementation with L-theanine has been shown to have a relaxing effect, reducing anxiety as well as heart rate and blood pressure in acute stressful events and during mentally challenging tasks.
L-theanine has been shown to reduce subjective experiences of stress and salivary α-amylase activity, a marker of sympathetic nervous system activity and the “fight or flight” response, during academic challenges. At a dosage of 200 mg daily, L-theanine has been shown to significantly reduce emotional symptoms of premenstrual syndrome, including irritability, anger, mood swings, and crying.
L-theanine continues to be studied for the impacts it may have on learning and memory, attention, mood, and even other mental health conditions such as schizophrenia.32 Orally, L-theanine has been shown to be well tolerated.
What does L-theanine do in the body? What are L-theanine benefits?
Neurotransmitters: L-theanine can positively impact the key neurotransmitters (brain chemical messengers) involved with stress, sleep, mood, focus, and memory. L-theanine benefits include enhancing the production of the neurotransmitters dopamine and serotonin, and also appears to play a role in the formation of GABA – a neurotransmitter that acts like a "brake" during times of stress. L-theanine helps establish balance in the neurotransmitter system, resulting in improvements in the mental/emotional and physical disturbances resulting from being overly stressed.
Because serotonin converts to melatonin in the pineal gland in your brain, improving serotonin levels ultimately results in improved melatonin levels, which in turn supports restful sleep.
So, does l-theanine help sleep? In one study, 30 healthy adults were given either 200 mg L-theanine dosage or a placebo daily for four weeks. The participants taking L- theanine took less time to fall asleep, had fewer sleep disturbances, and took fewer sleep medications, compared to the placebo group.3* Those taking L-theanine also had improved mental clarity, measured by verbal fluency, which isn’t hard to imagine – who doesn’t think better after a good night’s sleep?
Brain waves: L-theanine enhances brain alpha-wave activity, a marker of relaxation.* This effect has been observed to be most pronounced in individuals subjectively feeling the highest levels of stress.
In one study, healthy participants were given 50 mg L-theanine or a placebo, and brain waves were measured after taking the supplement and 45, 60, 90, and 105 minutes later.4 Alpha-wave production was significantly higher in the L-theanine group compared to the placebo group.
Another study of Japanese university students found that 200 mg of L-theanine led to increased brain alpha-waves and a subjective sense of relaxation, along with decreased stress-related beta-waves. In the same study, L-theanine administration also caused a dose-dependent relaxed, yet alert, state of mind without sedation, beginning approximately 40 minutes after ingestion. In this study, L-theanine was compared with water and GABA . Both L-theanine and GABA significantly increased alpha-wave production compared to water, although alpha-waves were increased more when the subjects took GABA than when they took L-theanine.
References
Nobre AC, et al. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.
Nobre AC, et al. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.
Nathan PJ, et al. The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30.
Yokogoshi H, et al. Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats. Neurochem Res. 1998;23(5):667-73.
Takeshima M, Miyazaki I, Murakami S, et al. l-Theanine protects against excess dopamine-induced neurotoxicity in the presence of astrocytes. J Clin Biochem Nutr. 2016 Sep;59(2):93-99.