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

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Synopsis

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

L-theanine is an amino acid found primarily in green tea, and it is often used as a dietary supplement for its calming effects. There is scientific evidence suggesting that L-theanine can modulate the body's stress response, which is closely linked to the cortisol system. Multiple human clinical studies have shown that L-theanine supplementation can reduce subjective stress and anxiety in healthy adults. For example, research published in peer-reviewed journals has demonstrated that doses of L-theanine (typically 200 mg) reduce salivary cortisol levels in response to acute stressors, such as mental arithmetic tasks or public speaking challenges. These effects are believed to occur through L-theanine's modulation of neurotransmitters, including GABA, serotonin, and dopamine, which can indirectly influence the hypothalamic-pituitary-adrenal (HPA) axis and cortisol secretion.

However, while the evidence supports an acute stress-reducing effect and some impact on cortisol, the data is still limited in terms of long-term effects and clinical outcomes. Most studies are small, short in duration, and focus on healthy participants rather than those with dysregulated cortisol rhythms or chronic stress conditions. Overall, L-theanine's use for cortisol modulation is justified by scientific research, but the evidence is moderate and more high-quality, long-term studies are needed for stronger conclusions.

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