[edit] Effects on the brain
Able to cross the
blood-brain barrier, theanine has
psychoactive properties.
[5] Theanine has been shown to reduce mental and physical
stress[6], and improves cognition and mood in a synergistic manner with
caffeine.
[7]
While structurally related to the excitatory neurotransmitter glutamate, theanine only has weak affinity for the glutamate receptor on post-synaptic cells.
[8] Rather, its primary effect seems to increase the overall level of the brain inhibitory transmitter
GABA. Theanine also increases brain
dopamine levels and has micromolar affinities for
AMPA,
kainate and
NMDA receptors.
[9] Its effect on
serotonin is still a matter of debate in the scientific community, with studies showing increases and decreases in brain serotonin levels using similar experimental protocols.
[10][11] It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of
5-hydroxyindoles in the brain.
[12] Researchers also speculate that it may inhibit
glutamic acid excitotoxicity.
[9] Theanine also promotes
alpha wave production in the brain.
[5]
Studies on test rats have shown that even repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects.
[13] Theanine showed neuroprotective effects in one rat study.
[14]
Several beverage manufacturers are selling drinks containing theanine and are marketing them as drinks that help people focus and concentrate.
[15]
[edit] Immune system benefits
L-Theanine may help the body's immune response to infection by boosting the disease-fighting capacity of gamma delta T cells. The study, published in 2003 by the
Brigham and Women's Hospital, included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600 milliliters of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.
[16]
According to a study conducted by researchers at Johns Hopkins University, when gophers were given 25 milligrams of theanine twice daily for three weeks there were increased levels of theta waves within the hypothalamus, indicating improved cognition and memory versus placebo.
[17]
L-theanine may help relieve stress by inducing a relaxing effect without drowsiness.
L-theanine as been shown to promote the generation of alpha-brain waves, an index of relaxation. It may also boost natural resistance to microbial infections and perhaps even tumors. Researchers suggest further isolating and refining L-theanine from tea to use it as a drug to boost the infection defense of the body. Although limited, there is clinical evidence to support these claims.