Evidence supporting the use of: L-theanine
For the body system: GABA

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Synopsis

Source of validity: Scientific
Rating (out of 5): 3

L-theanine, an amino acid predominantly found in green tea, has been studied for its potential effects on the central nervous system, including its influence on the GABAergic system. Scientific evidence suggests that L-theanine can modulate neurotransmitters, particularly by increasing the levels of GABA (gamma-aminobutyric acid), as well as dopamine and serotonin, in the brain. GABA is the primary inhibitory neurotransmitter responsible for promoting relaxation and reducing neuronal excitability.

Several animal and in vitro studies indicate that L-theanine may enhance GABAergic activity, contributing to its anxiolytic (anxiety-reducing) effects. For example, a study published in Phytotherapy Research (2005) found that L-theanine administration increased brain GABA levels in rats. Human studies are more limited but suggest that L-theanine supplementation can promote relaxation without sedation, possibly through GABA modulation. Clinical trials have demonstrated that L-theanine can reduce stress and improve sleep quality, outcomes often linked to increased GABA activity.

However, the direct evidence in humans specifically linking L-theanine supplementation to measurable increases in GABA levels or direct GABA receptor modulation is relatively modest. Most research supports a general calming effect, likely through combined neurotransmitter effects, rather than a robust, well-characterized impact solely via the GABA system. Thus, while the use of L-theanine for supporting the GABA system is supported by scientific evidence, the strength and specificity of this evidence are moderate.

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