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

2019-10-03
Nutrients 11(10)
- Shinsuke Hidese
- Shintaro Ogawa
- Miho Ota
- Ikki Ishida
- Zenta Yasukawa
- Makoto Ozeki
- Hiroshi Kunugi

PubMed: 31623400
DOI: 10.3390/nu11102362

Study Design

Type: Randomized Controlled Trial (RCT)
Sample size: n = 30
Population: 30 healthy adults (nine men and 21 women; age: 48.3 ± 11.9 years) who had no major psychiatric illness
Methods: randomized, placebo-controlled, crossover, and double-blind trial, 200 mg/day L-theanine or placebo for four weeks
Blinding: Double-blind
Duration: four weeks
Funding: Unclear

Rigorous Journal

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.

Research Insights

L-Theanine→Improved Cognitive Function
executive function scores improved after L-theanine administration (p = 0.031)
Effect
Beneficial
Effect size
Small
Dose
200 mg/day
L-Theanine→Improved Sleep Quality
Pittsburgh Sleep Quality Index (PSQI) scores decreased after L-theanine administration (p = 0.013)
Effect
Beneficial
Effect size
Moderate
Dose
200 mg/day
L-Theanine→Improved Verbal Fluency
verbal fluency ... scores improved after L-theanine administration (p = 0.001)
Effect
Beneficial
Effect size
Moderate
Dose
200 mg/day
L-Theanine→Reduced Circadian Sleep Disturbance
PSQI subscale scores for ... sleep disturbance ... reduced after L-theanine administration, compared to the placebo administration (all p < 0.05)
Effect
Beneficial
Effect size
Small
Dose
200 mg/day
L-Theanine→Reduced Depression Symptoms
Self-rating Depression Scale ... scores decreased after L-theanine administration (p = 0.019)
Effect
Beneficial
Effect size
Moderate
Dose
200 mg/day
L-Theanine→Reduced Sleep Latency
PSQI subscale scores for sleep latency ... reduced after L-theanine administration, compared to the placebo administration (all p < 0.05)
Effect
Beneficial
Effect size
Small
Dose
200 mg/day
L-Theanine→Reduced Sleep Medication Use
PSQI subscale scores for ... use of sleep medication reduced after L-theanine administration, compared to the placebo administration (all p < 0.05)
Effect
Beneficial
Effect size
Small
Dose
200 mg/day
L-Theanine→Reduced Trait Anxiety
State-Trait Anxiety Inventory-trait ... scores decreased after L-theanine administration (p = 0.006)
Effect
Beneficial
Effect size
Moderate
Dose
200 mg/day