L-Theanine
L-Theanine (γ-glutamylethylamide) is a dietary supplement with 6 published peer-reviewed studies involving 319 participants, researched for Sleep.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Sleep
StrongResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Sleep
To examine the effects of L-theanine on cognitive functions and stress-related symptoms, including sleep disorders, in healthy adults.
Study Type
Randomised, placebo-controlled, crossover, and double-blind trial
Purpose
To examine the effects of L-theanine on cognitive functions and stress-related symptoms, including sleep disorders, in healthy adults.
Dose
200 mg/day of L-theanine or placebo
Participants
30 men and women with an average age of 48 years
Duration
4 weeks
Results
Participants who took L-theanine demonstrated significant improvements in overall sleep quality, with less trouble falling asleep, fewer disturbances, and less need for sleep medication compared to the placebo. Additionally, cognitive skills improved, and stress-related symptoms like depression and anxiety decreased. Overall, the study suggests that L-theanine may enhance both sleep and mental performance more effectively than the placebo.
How They Measured It
Stress-related symptoms were assessed using self-reported questionnaires, including the Self-rating Depression Scale for depression, the State-Trait Anxiety Inventory for anxiety, and the Pittsburgh Sleep Quality Index for sleep quality and disturbances. The study also utilised several cognitive assessments to evaluate the effects of L-theanine on cognitive functions.
To investigate the effects of known sleep-support supplements, including L-theanine, on life habits, sleep conditions, and sleep problems.
Study Type
Open, randomised, crossover intervention trial
Purpose
To investigate the effects of known sleep-support supplements, including L-theanine, on life habits, sleep conditions, and sleep problems.
Dose
Treatment 1: 200 mg/day of L-theanine Treatment 2: 111.1 mg/day of GABA Treatment 3: 50 mg/day of Apocynum venetum leaf extract Treatment 4: 300 mg/day of L-serine Treatment 5: Mindfulness video Treatment 6: Placebo
Participants
106 male and female participants with an average age 46 years
Duration
7 days of intervention per group
Results
The researchers observed that L-theanine significantly improved sleep quality, especially for individuals struggling to fall asleep, stay asleep, or feel refreshed in the morning. People with good habits, such as less screen time and regular exercise, showed significantly better results. This suggests that combining physical activity and healthy lifestyle habits with L-theanine may lead to better sleep.
How They Measured It
Sleep quality was assessed using a self-reported questionnaire called the Pittsburgh Sleep Quality Index, which measures seven areas: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction.
To investigate the effects of L-theanine in combination with alpha-s1-casein tryptic hydrolysate (a protein derived from cow's milk) on sleep quality in working adults with sleep disorders/insomnia.
Study Type
Randomised, double-blind, placebo controlled, crossover trial
Purpose
To investigate the effects of L-theanine in combination with alpha-s1-casein tryptic hydrolysate (a protein derived from cow's milk) on sleep quality in working adults with sleep disorders/insomnia.
Dose
50 mg/day of L-theanine with 150 mg/day of alpha-s1-casein tryptic hydrolysate (CTH) or placebo
Participants
39 men and women with an average age of 37 years
Duration
4 weeks
Results
The study found a significant association between L-theanine combined with alpha-s1-casein and improved sleep quality. The participants in the L-theanine group reported falling asleep faster, sleeping longer, and having better-quality sleep, while also feeling more alert during the day. In addition, those who took the supplement slept 45 minutes longer than those who took a placebo, with the biggest improvements seen in both sleep duration and sleep quality.
How They Measured It
Sleep quality was assessed using a self-reported questionnaire called the Pittsburgh Sleep Quality Index, which measures seven areas: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction.
To examine the effects of L-theanine on depressive symptoms, anxiety, sleep disturbance, and cognitive impairments in patients with major depressive disorders
Study Type
Clinical trial (uncontrolled)
Purpose
To examine the effects of L-theanine on depressive symptoms, anxiety, sleep disturbance, and cognitive impairments in patients with major depressive disorders
Dose
250 mg/day L theanine tablets
Participants
20 male and female patients with an average age of 43 years
Duration
8 weeks
Results
The study found that L-theanine administration is associated with a significant improvement in sleep disturbance among patients with major depressive disorder. The study also noted that some patients reported increased sleep duration and slightly increased dream activity, suggesting a positive impact on sleep patterns.
How They Measured It
Sleep quality was assessed using a self-reported questionnaire called the Pittsburgh Sleep Quality Index, which measures seven areas: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction.
To explore the sleep-improving effects of a lower dose L-theanine (100 mg/day) in middle-aged and older men.
Study Type
Randomised, placebo-controlled, double-blind, crossover trial
Purpose
To explore the sleep-improving effects of a lower dose L-theanine (100 mg/day) in middle-aged and older men.
Dose
100 mg/day of L-theanine or placebo
Participants
24 men with an average age of 47 years
Duration
1 week
Results
Overall, there was no significant difference in sleep quality between the theanine and placebo groups. However, for those under 50 and participants who drank green tea less than 3-4 times a week, the researchers observed that theanine significantly improved stage 2 non-REM sleep. Stage 2 non-REM sleep helps lower heart rate, cool the body, and rest the brain, leading to more refreshing and higher-quality sleep.
How They Measured It
Sleep quality was assessed using a portable electroencephalogram (EEG) monitoring device, which measures brain activity during sleep. Participants placed sensors on their forehead and behind their ears, which tracked how long they slept, how quickly they fell asleep, time spent in deep and light sleep, and how often they woke up.
To evaluate the effects of a combination of magnesium, vitamins B6, B9, B12, rhodiola, and L-theanine (Mg-Teadiola) on stress and stress-related quality of life parameters, including sleep and pain perception, in chronically stressed individuals.
Study Type
Randomised, single-blind, placebo-controlled trial
Purpose
To evaluate the effects of a combination of magnesium, vitamins B6, B9, B12, rhodiola, and L-theanine (Mg-Teadiola) on stress and stress-related quality of life parameters, including sleep and pain perception, in chronically stressed individuals.
Dose
125 mg/d L-theanine with 150 mg/day of magnesium, 222 mg/d rhodiola, 0.7 mg vit B6, 0.1 mg of vit B9, and 1.25 mcg vit B12, or placebo
Participants
100 chronically stressed, bu otherwise healthy men and women aged 18-65 years
Duration
28 days
Results
Mg-Teadiola showed potential for improving sleep-related quality of life, particularly in significantly reducing daytime dysfunction due to sleepiness in the longer term. The study also found an association between Mg-Teadiola supplementation and significant decreases in stress scores.
How They Measured It
Sleep quality was assessed before and after the intervention using the Pittsburgh Sleep Quality Index, a self-reported questionnaire which measures seven areas: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction.
Frequently Asked Questions
Common questions about L-Theanine research
There are currently 6 peer-reviewed studies on L-Theanine (γ-glutamylethylamide), involving 319 total participants. Research covers Sleep. The overall evidence strength is rated as Strong.
The evidence is currently rated as "Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (6 human studies), and reported outcomes.
L-Theanine has been researched for: Sleep. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 6 out of 6 studies are human trials. Human trials carry more weight in our evidence scoring system.
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