L-Theanine

Authors:

Shinsuke Hidese

Findings:

Four weeks of L-theanine administration decreased self-reported stress-related symptoms (depression, anxiety, sleep issues including latency, disturbance, medication use) and improved cognitive functions (verbal fluency, executive function) compared to placebo in healthy adults. Stratified analysis showed improved verbal fluency (especially letter fluency) in individuals with lower baseline scores. L-theanine may promote mental health in those with stress-related ailments and cognitive impairments.

Participants:

Healthy adults (N=30; nine men and 21 women; age: 48.3 ± 11.9 years) who had no major psychiatric illness.

Dosage:

200 mg/day for four weeks.

Study Quality Assessment:

Randomized, placebo-controlled, crossover, and double-blind trial. N=30. Conflict of interest: Two authors are employees of the company that supplied the L-theanine and placebo tablets.

All Effects:

Findings:

L-theanine is possibly effective for improving mental function (focus) in healthy people, though combining it with caffeine may not offer additional benefits over either alone. There is insufficient reliable information or 'no good scientific evidence' for its use in anxiety, mental impairment, stress, and other conditions. It might cause mild side effects like headache or sleepiness.

Participants:

Mentions 'healthy people' regarding cognitive function effectiveness and safety data for 'males aged 8-12 years'.

Dosage:

Adults have most often used 200-400 mg by mouth daily for 4-8 weeks. Doses up to 900 mg daily have been used safely for 8 weeks. In males aged 8-12 years, doses of 400 mg daily have been safely used for up to 6 weeks.

Study Quality Assessment:

States there is 'no good scientific evidence' to support uses for anxiety, mental impairment, stress, and other conditions. Safety data mentioned is based on 'short-term' use (up to 8 weeks for adults, up to 6 weeks for children).

All Effects:

Findings:

A single dose of l-theanine reduced reaction time in attention tasks (Stroop test) and improved working memory performance (increased correct answers, decreased omission errors in 4-Part CPT). The study suggests l-theanine may improve attention, working memory, and executive functions.

Participants:

Japanese men and women aged 50-69 years with Mini Mental State Examination-Japanese version score of 24 or higher.

Dosage:

Evaluations performed after a single dose and after 12 weeks of regular intake (specific mg dosage not mentioned).

Study Quality Assessment:

Double-blind, randomized, placebo-controlled study. Used Cognitrax test battery. Clinical Trial No.: UMIN000033812. Funding source (ITO EN, Ltd.) and roles of Contract Research Organization (Huma R&D Corp.) and statistical analysis provider (Kureha Special Laboratory Co., Ltd.) disclosed. Conflict of interest statement provided.

All Effects:

Authors:

Shuna Chen

Findings:

L-theanine demonstrates immunomodulatory effects, reducing exercise-induced immunosuppression and preventing colds/flu in humans. Animal and cell studies show it regulates inflammation, nerve damage, gut immunity, and tumor immunity by modulating γδT lymphocyte function, glutathione (GSH) synthesis, antioxidant capacity, and cytokine/neurotransmitter secretion. It also shows potential as an immunomodulator in animal production (poultry, livestock).

Participants:

Review covers studies involving: Humans (athletes, health care workers, older people, gastric cancer patients, colorectal/gastrointestinal cancer patients); Animal models (mice, rats, broiler chickens, meat ducks, weanling piglets, lactating cows).

Dosage:

Review mentions various dosages from cited studies: 4 g/kg (rats, pharmacokinetics); >20 g/kg (mice, MTD); 1.5-4 g/kg daily for 13 weeks (rats, subchronic tox); 200 mg/kg (rats, OA model; broilers, antioxidant); L-theanine/cystine combo (5:2 w/w, mice, gut); Dose-dependent effects noted (mice, intestinal ischemia-reperfusion; rats, OA model); Dietary supplementation mentioned for piglets and broilers.

Study Quality Assessment:

Review discusses studies including: Randomized, double-blind, placebo-controlled trials (human cold/flu prevention); In vitro and animal model studies (mice, rats); Pharmacokinetic and toxicity studies (mice, rats); Mentions specific methods like cytokine measurements (e.g., IL-6, IFN-γ, TNF-α), GSH levels, γδT cell function, NK cell activity, lymphocyte/neutrophil counts, oxidative stress markers (ROS, MDA, SOD, CAT), protein expression/signaling pathway analysis (e.g., NF-κB, MAPK, Akt/mTOR), histopathology, behavioral assessments. Funding sources acknowledged for the review itself.

All Effects:

Findings:

L-theanine treatment reduced immunohistochemical hallmarks of Parkinson's disease (Lewy bodies, α-synuclein), increased tyrosine hydroxylase-positive cells, and improved motor dysfunction in MPTP-induced model mice. It also reduced levels of pro-inflammatory mediators and pro-apoptotic proteins, and regulated oxidative stress factors by targeting WNT/β-catenin signaling via the MAPK pathway. The results indicate L-theanine has neuroprotective and anti-inflammatory effects potentially beneficial for Parkinson's disease.

Participants:

MPTP-induced SH-SY5Y cells (in vitro); Parkinson's model mice (in vivo)

Dosage:

SH-SY5Y cells treated with L-theanine concentrations of 50, 100, 200, and 500 μg/mL. Dosage for model mice not specified in the provided text.

Study Quality Assessment:

In vitro study using SH-SY5Y cells; In vivo study using MPTP-induced Parkinson's model mice; Methods mentioned: immunohistochemistry, tyrosine hydroxylase cell counts, rotarod test, measurement of pro-inflammatory mediators (TNF-α, IL-6, COX-2, MAC-1), pro-apoptotic proteins (Bcl-2, caspase-3, p53, PARP-1), oxidative stress factors (SOD-1, GST, NOX-4), and signaling pathway analysis (WNT/β-catenin, MAPK); Conflict of interest statement: 'The authors declare that there are no conflicts of interest.'

All Effects: