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Randomized Controlled Trial
, 11 (10)

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial

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Randomized Controlled Trial

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial

Shinsuke Hidese et al. Nutrients.

Abstract

This randomized, placebo-controlled, crossover, and double-blind trial aimed to examine the possible effects of four weeks L-theanine administration on stress-related symptoms and cognitive functions in healthy adults. Participants were 30 individuals (nine men and 21 women; age: 48.3 ± 11.9 years) who had no major psychiatric illness. L-theanine (200 mg/day) or placebo tablets were randomly and blindly assigned for four-week administration. For stress-related symptoms, Self-rating Depression Scale, State-Trait Anxiety Inventory-trait, and Pittsburgh Sleep Quality Index (PSQI) scores decreased after L-theanine administration (p = 0.019, 0.006, and 0.013, respectively). The PSQI subscale scores for sleep latency, sleep disturbance, and use of sleep medication reduced after L-theanine administration, compared to the placebo administration (all p < 0.05). For cognitive functions, verbal fluency and executive function scores improved after L-theanine administration (p = 0.001 and 0.031, respectively). Stratified analyses revealed that scores for verbal fluency (p = 0.002), especially letter fluency (p = 0.002), increased after L-theanine administration, compared to the placebo administration, in individuals who were sub-grouped into the lower half by the median split based on the mean pretreatment scores. Our findings suggest that L-theanine has the potential to promote mental health in the general population with stress-related ailments and cognitive impairments.

Keywords: L-theanine; cognition; emotion; sleep; stress.

Conflict of interest statement

Yasukawa Z. and Ozeki M. are employees of Taiyo Kagaku Co., Ltd. which supplied the L-theanine and placebo tablets used in this trial.

Figures

Figure 1
Figure 1
Stress-related symptom scores after 4 weeks L-theanine or placebo administration. The Wilcoxon signed-rank test revealed that the Self-rating Depression Scale, State-Trait Anxiety Inventory-trait, and Pittsburgh Sleep Quality Index scores were significantly decreased in the L-theanine administration (n = 30), while there was no significant change in the placebo administration (n = 30). * p < 0.05, ** p < 0.01. N.S., not significant.
Figure 2
Figure 2
Cognitive function scores after 4 weeks L-theanine or placebo administration. The Wilcoxon signed-rank test revealed that the Brief Assessment of Cognition in Schizophrenia (BACS) verbal fluency and executive function scores were significantly decreased in the L-theanine administration (n = 30), while there was no significant change in the placebo administration (n = 30). * p < 0.05, ** p < 0.01. N.S.: Not significant.

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