Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction.
Level 5 - mechanism / opinion, no new human data
Narrative review describing pharmacological mechanisms and summarizing human and preclinical data
PubMed 21477654 · doi:10.1016/j.phrs.2011.03.010
What was done
The authors reviewed pharmacological mechanisms of theanine (gamma-glutamylethylamide from Camellia sinensis), including blood-brain barrier transport, glutamate receptor antagonism (AMPA/kainate), and glutamine transporter inhibition. They also summarized findings from an investigation of elderly volunteers with normal or slight cognitive dysfunction who ingested powdered green tea containing 47.5 mg/day of theanine versus placebo.
What was found
Mechanistically, theanine exhibits low-affinity antagonism at AMPA and kainate receptors and strongly inhibits extracellular glutamine incorporation into neurons via glutamine transporters, suppressing glutaminase conversion to glutamate. In the summarized trial of elderly individuals, consumption of 47.5 mg/day theanine via green tea powder resulted in significantly lower cognitive decline compared to placebo. No exact numerical scores, sample sizes, or p-values are reported in the abstract.
Why it matters
The review outlines a specific biochemical pathway—glutamine transporter inhibition rather than direct high-affinity glutamate receptor blockade—by which theanine may confer neuroprotection and support cognitive function in aging.
Limits
This is a narrative review without systematic search or meta-analytic methodology. The abstract omits participant sample size, study duration, specific cognitive testing instruments, and quantitative effect sizes for the cited human trial. Additionally, the human trial tested whole green tea powder rather than isolated theanine, confounding the specific active component.
Cited by
- supports L-theanine crosses the blood-brain barrier.