Science builds for L-Theanine’s cognitive benefits: RCT

By Stephen Daniells

- Last updated on GMT

© Warunporn Thangthongtip / Getty Images
© Warunporn Thangthongtip / Getty Images

Related tags L-theanine theanine Cognitive function

Supplements containing L-theanine from tea my boost measures of cognitive function such as attention and memory in middle-aged and older adults, suggests a new study from Japan.

Twelve weeks of supplementation 100.6 mg per day of L-theanine was associated with cognitive improvements, including executive functions in middle-aged and older adults with self-reported declines in their cognitive function, according to data published in the Journal of Medicinal Food.

“In this study, the dose of theanine was set at 100.6 mg for the purpose of clearly showing the effect of theanine alone,” ​wrote scientists from Japanese multinational tea specialists Ito En, Ltd. and Tokyo Skytree Station Medical Clinic.

“A single dose of l-theanine reduced reaction time in the attention task and increased correct answers and decreased the number of omission errors in the working memory task. This suggests that l-theanine may improve working memory and executive function based on the improvement in attention.”


L-theanine, an amino acid found in tea leaves, is thought to help reduce stress, promote relaxation and improve the quality of sleep. L-theanine is found in tea leaves in low concentrations (less than 2%), which means that effective dosage levels (of 100 – 200 mg/day) cannot be delivered from drinking tea.

The ingredient’s potential cognitive benefits have been reported previously, with, for example, a 2019 paper in Nutrients​ stating that l-theanine may boost verbal fluency, stress-related symptoms, such as depression, anxiety-trait, and sleep problems, compared to placebo.

Like the 2019 paper, the new study used Taiyo’s Suntheanine-branded ingredient.

Sixty-nine middle-aged and older Japanese men and women were recruited to participate in the double-blind, randomized, placebo-controlled study. Participants were randomly assigned to receive either L-theanine (100.6 mg) or placebo for 12 weeks. The researchers used a cognitive test called Cognitrax to assess cognitive function after a single dose and again after 12 weeks.

The results indicated that the single l-theanine dose was associated with reductions in reaction time to the attention tasks. The researchers also found that the single dose led to increases in the number of correct answers and decreases in the number of omission errors in working memory tasks.

However, no statistically significant benefits were reported after 12 weeks (chronic) supplementation.

“Future studies are therefore required to investigate the differential effects of single dose and daily intake of l-theanine on brain structure and cognitive function,” ​concluded the researchers.

Source: Journal of Medicinal Food
Vol. 24, No. 4, doi: 10.1089/jmf.2020.4803
“Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study”
Authors: Y. Baba, et al.

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