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

Summary & key facts

In a small, carefully done study, 30 healthy adults (about 48 years old on average) took 200 mg of L-theanine each day for four weeks and also took a look-alike placebo for four weeks. Neither the people nor the researchers knew which pills were which while testing. After the L-theanine periods, people reported less depressed mood and less anxiety, and their sleep quality improved. Simple thinking tests showed better word-finding and some improvement in planning and problem-solving. The results suggest L-theanine might help with stress-related mood, sleep, and some thinking skills, but the study was small, short, and done in healthy people, so it is not proof that it will work for everyone.

Key facts:

• Thirty people took part, nine men and 21 women, with an average age of about 48 years.
• Each person took 200 mg of L-theanine per day for four weeks, and in another period they took a placebo (a fake pill) for four weeks; the order was random and nobody knew which pill they were taking at the time.
• After the L-theanine periods, scores for depressed mood and general anxiety were lower than before, and sleep quality scores were better compared to the placebo periods.
• Aspects of sleep that improved after L-theanine included falling asleep faster (sleep latency), fewer sleep disruptions, and less use of sleep medication.
• On simple cognitive tests, people showed better verbal fluency (finding words) and better executive function (planning and switching between tasks) after L-theanine than after placebo.
• People who started with lower word-finding ability showed the largest gains, especially on tests that ask you to list words starting with a certain letter.
• Because only 30 healthy adults were studied for a short time, these findings suggest possible benefits but do not prove L-theanine will help everyone or treat disorders.
• The study used a strong design (each person tried both L-theanine and placebo, and the testing was blind), which makes the comparison between L-theanine and placebo more reliable.

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.

Topics

Diet and metabolism studies Tea Polyphenols and Effects Tryptophan and brain disorders

Categories

Biological Psychiatry Life Sciences Neuroscience

Tags

Biology Clinical psychology Cognition Food science Green tea Internal medicine Linguistics Medicine Philosophy Psychiatry Randomized controlled trial Stress (linguistics) Theanine

Substances

Other

Conditions & symptoms

Anxiety Depression Sleep disorder Anxiety or worry Difficulty focusing Poor sleep Sadness or low mood