L-Theanine was originally found in green tea and it is also present in some mushrooms. It was discovered by the researcher Yajiro Sakato in 1949 at the Ministry of Agriculture and Forestry in Kyoto, Japan.
Theanine accounts for approximately 50% of the total amino acids in green tea leaves. It comprises about 1–2% of the total dry weight of the green tea leaves, and the median amount of L-theanine per cup of green tea is 8-30 mg.
Theanine occurs as two isomers called D-Theanine and L-Theanine. L-Theanine is the isomer found in tea and supplements.
L-Theanine has a chemical structure that is very similar to glutamate, a naturally occurring amino acid in the body that helps transmit nerve impulses in the brain. L-Theanine crosses the blood-brain barrier where it exerts its actions. Some of the effects of theanine appear to be similar to glutamate, but some effects appear to block glutamate.
L-Theanine increases brain serotonin - the brain's main neurotransmitter responsible for mood and happiness, and it also increases dopamine - a neurotransmitter that is involved in a person's sense of reward and motivation. L-Theanine also boosts levels of GABA - the main neurotransmitter involved in inhibiting the overactivity of brain cells.
Although the mechanism of action of L-Theanine is not fully understood, the overall effect of L-Theanine is to increase 'feel good' neurotransmitter levels and inhibitory neurotransmitter levels as well as block overproduction of excitatory neurotransmitters.
Another interesting mechanism of L-Theanine is its ability to increase alpha brain wave activity. Alpha brainwave activity is associated with increased performance under stress, improved learning and concentration, as well as decreased anxiety. Alpha brain waves indicate a brain state that is relaxed yet alert. We often have elevated alpha brain wave activity after waking up, and meditation is associated with increased alpha brain waves.
People have hailed the health benefits of green tea for centuries. In fact, tea is so popular it is the second most consumed beverage in the world, after water! However, it is only in the last decade or so that science has turned its attention to the benefits of green tea.
The most common reasons people take L-Theanine are for concentration, focus and relaxation. Emerging science supports a role for L-Theanine protecting the brain against age-related degeneration also.
Hidese, S., et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients, 11, 2362; 2019.
Hidese, S., et al. Effects of chronic L-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatrica 2017.
Ota, M., et al. Effect of L-theanine on sensorimotor gating in healthy human subjects. Psychiatry and Clinical Neurosciences; 68: 337–343; 2014.
Baba, Y., et al. Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study. J Med Food 24 (4), 333–341; 2021.
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