Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-theanine is an amino acid commonly found in tea leaves, particularly green tea, and is noted for its calming effects and cognitive benefits. Its use in supporting or treating Alzheimer’s Disease (AD) is justified primarily by emerging scientific interest, though evidence remains preliminary. Preclinical studies have shown that L-theanine may exert neuroprotective effects through several mechanisms: reducing oxidative stress, modulating neurotransmitter levels, and inhibiting neuronal cell death. For example, animal studies suggest that L-theanine may improve cognitive function, reduce amyloid-beta aggregation (a hallmark of AD pathology), and enhance neurogenesis. A 2019 study published in "Nutrients" highlighted L-theanine's potential to attenuate memory impairment and neuronal damage in mouse models of Alzheimer's. However, human clinical trials are limited. Most human research has focused on L-theanine’s effects on attention, stress, and general cognitive health, rather than specifically on Alzheimer’s Disease. Small-scale studies combining L-theanine with other compounds, such as caffeine, have shown modest improvements in attention and reaction time but not in disease progression or symptom mitigation in AD patients. In summary, while there is some preclinical evidence supporting a neuroprotective role for L-theanine relevant to Alzheimer’s Disease, direct clinical evidence in human AD patients is lacking. Thus, the scientific justification is preliminary, and the strength of evidence is low (rated 2 out of 5).

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