Taiyo study supports L-Theanine for cognitive benefits

By Stephen Daniells

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L-theanine is an amino acid found in tea leaves.   Image © Getty Images / Irina Vodneva
L-theanine is an amino acid found in tea leaves. Image © Getty Images / Irina Vodneva

Related tags Tea theanine Cognitive function

Supplements containing L-theanine from tea my boost measures of cognitive function such as verbal fluency and executive function, compared to placebo in healthy adults, suggests a new study from Taiyo.

Scores for stress-related symptoms, such as depression, anxiety-trait, and sleep problems, were improved in otherwise healthy people received 200 mg per day of Taiyo’s Suntheanine-branded L-theanine ingredient for four weeks.

In addition, cognitive function improved in these same people, according to data published in the journal Nutrients​.

“The reduction in sleep quality problems (disturbances in sleep latency, sleep disturbance, and use of sleep medication) was greater in the L-theanine administration compared to the placebo administration, while verbal fluency, especially letter fluency, was improved in the L-theanine administration among individuals who showed relatively low performance at pretreatment,”​ wrote the scientists.

“Therefore, L-theanine may be a suitable nutraceutical ingredient for improving mental conditions in a healthy population.”


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.

For the new study, the researchers recruited 30 healthy men and women with an average age of 48 to participate in their randomized, placebo-controlled, crossover, and double-blind trial. Participants were randomly assigned to receive either 200 mg per day of L-Theanine (Suntheanine) or placebo for four months.

Stress-related symptoms were measured using the Self-rating Depression Scale, State-Trait Anxiety Inventory-trait, and Pittsburgh Sleep Quality Index (PSQI). Results indicated that L-theanine group experienced reductions in the PSQI scores for sleep latency, sleep disturbance, and use of sleep medication, compared to placebo

In addition, verbal fluency and executive function scores were observed to have improved in the L-theanine group particularly in people with poorer cognitive function at the start of the study, compared to placebo.

“Our findings suggest that L-theanine has the potential to promote mental health in the general population with stress-related ailments and cognitive impairments,” ​concluded the researchers.

Source: Nutrients
2019, 11(10), 2362; doi: 10.3390/nu11102362
“Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial”
Authors: S. Hidese et al.