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

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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 is commonly used to support the nervous system, particularly for its purported calming effects. Scientific studies have shown that L-theanine can cross the blood-brain barrier and influence brain function. Multiple human clinical trials have reported that L-theanine supplementation can promote relaxation without sedation, reduce stress, and improve cognitive performance, especially in combination with caffeine. The mechanism is believed to involve modulation of neurotransmitters such as GABA, serotonin, and dopamine, as well as promoting alpha brain wave activity, which is associated with a relaxed but alert mental state.

A 2016 systematic review published in the journal Pharmacological Research found that L-theanine supplementation was associated with reduced stress and anxiety in human subjects. Other randomized, placebo-controlled studies have found improvements in attention and reductions in physiological markers of stress, such as heart rate and salivary cortisol.

While most studies are of short duration and use relatively small sample sizes, the evidence base is growing. L-theanine is generally regarded as safe, with few reported side effects. While more large-scale, long-term studies are needed to confirm these effects, current research supports its use as a supplement to support the nervous system, particularly for stress and anxiety reduction.

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