Since ancient times, it has been said that drinking green tea brings relaxation. The substance that is responsible for a sense of relaxation, is L-theanine.
L-theanine is a unique amino acid found almost solely in tea plants and the main component responsible for the exotic taste of ‘green’ tea. L-theanine makes up around 1-2% of the dry weight of tea. L-theanine from tea is bioavailable in humans and is able to penetrate the blood brain barrier within 15-25 minutes following the consumption of tea.
L-theanine increases alpha wave brain activity, a condition that is associated with relaxation. Brain waves are classified into four types, namely α,β,δ and θ-waves, based on mental conditions. Generation of α-waves is considered to be an index of relaxation. In human volunteers, α-waves were generated in the occipital and parietal regions of the brain surface within 25 min after the oral administration of theanine (50–200 mg), signifying relaxation without causing drowsiness.
Essentially, L-theanine is a compound that stimulates relaxation but without sedation. In addition to the relaxing effects of L-theanine, the compound also aids in memory formation. One of the most common uses for this amino acid is to decrease stress and anxiety. These studies have found that theanine can affect the serotonin and dopamine levels in the brain, creating an anxiolytic effect.
A Japanese study found that college students experienced less anxiety after doses of L-theanine. Also, those participants taking this amino acid had less elevated blood pressure after exposure to physical or psychological stress compared with those taking the placebo.
Canadian scientists found that L-theanine administration could help to reduce the severity of some sleep disorders in boys with attention-deficit hyperactivity disorder (ADHD)7. L-theanine may also have a positive role in antipsychotic treatments for patients suffering from schizophrenia.
It is important to note that the above mentioned human studies have been short-term and with a small participant base. While the results are positive, more research is necessary into the potential anti-stress and anxiety effects of L-theanine.
Generally, a typical cup of black tea will have around 6mg of L-theanine. A cup of green tea will have around 8mg of this amino acid.