Green Tea

Findings:

Green tea contains polyphenol flavonoids like catechins. Epigallocatechin 3-gallate (EGCG) is identified as the most abundant and potent catechin in green tea.

Findings:

Reviewed studies showed evidence that green tea influences psychopathological symptoms (e.g., anxiety reduction), cognition (e.g., benefits in memory and attention), and brain function (e.g., activation of working memory via fMRI). Beneficial cognitive effects were observed with the combined influence of caffeine and l-theanine, with lesser impact from separate administration.

Participants:

Humans

Study Quality Assessment:

Systematic review of 21 studies (4 randomised controlled trials, 12 cross-over studies, 4 cross-sectional studies, 1 cohort study). Quality assessed using adapted DELPHI-list (average score 8.06/9) and adapted Newcastle-Ottawa assessment scale (average score 6.7/9). Structured according to PRISMA statement. MeSH terms include 'Randomized Controlled Trials as Topic'.

All Effects:

Findings:

Daily consumption of 2g matcha for 12 months led to significant improvements in social acuity score (perception of facial emotions). Primary cognitive outcomes (Montreal Cognitive Assessment, Alzheimer's Disease Cooperative Study Activity of Daily Living scores) showed no significant changes. A trend toward improvement in sleep quality (Pittsburgh Sleep Quality Index scores) was observed. Regular matcha consumption could improve emotional perception and sleep quality in older adults with mild cognitive decline.

Participants:

Ninety-nine older adults (N=99), including 64 with subjective cognitive decline and 35 with mild cognitive impairment.

Dosage:

2 g of matcha daily for 12 months.

Study Quality Assessment:

Randomized controlled trial (RCT), double-blind, placebo-controlled, N=99, duration 12 months. Participants stratified by age at baseline and APOE genotype. Analysis using mixed-effects model. Specific cognitive tests (perception of facial emotions, Montreal Cognitive Assessment, Alzheimer's Disease Cooperative Study Activity of Daily Living) and sleep quality measure (Pittsburgh Sleep Quality Index) used. Competing interests disclosed (authors employed by MCBI Inc. and ITO EN, LTD.). Stated 'no external funding'.

All Effects:

Findings:

The combination of EGCG and L-theanine demonstrated synergistic effects in protecting differentiated PC12 nerve cells against Aβ25–35-induced damage. This synergy involved inhibiting amyloid stress and inflammation, promoting metabolism (including mitochondrial activity and energy production), regulating the cell cycle towards quiescence (increased G0/G1 phase, decreased cyclins), promoting axonal growth (increased GAP43), and maintaining protein structural fidelity. These findings suggest EGCG + L-theanine promotes nerve cell repair and regeneration.

Participants:

In vitro study using an Alzheimer's Disease (AD) model established with Aβ25–35-induced differentiated neural cell line PC12 cells (Rat pheochromocytoma cell line). RNA sequencing data compared against Rattus norvegicus reference.

Dosage:

Cell experiments used final concentrations of 50 μM Aβ25–35 alone or co-incubated with 50 μM EGCG, 50 μM L-theanine, or both 50 μM EGCG + 50 μM L-theanine. Preliminary tests showed EGCG cytotoxicity at 100 μM and L-theanine growth promotion up to 100 μM.

Study Quality Assessment:

Original Research article published in Front. Nutr. Methods mentioned: MTT assay, ThT fluorescence detection, Transmission Electron Microscopy (TEM), Flow cytometry (cell cycle, apoptosis), Fourier Transform Infrared Spectroscopy (FTIR), JC-1 staining (mitochondrial membrane potential), DAPI staining, LDH cytotoxicity assay, ATP detection, Western blotting, Enzyme-linked immunosorbent assay (ELISA), BODIPY fluorescent staining, RNA sequencing (RNA-seq). Statistical analysis: one-way ANOVA with Turkey’s multiple comparison test (p < 0.05, p < 0.01). Funding sources listed. Conflict of interest statement included. Data availability mentioned (NCBI BioSample database, accession SAMN29216840).

All Effects:

Findings:

The review suggests that L-theanine (L-THE) supplementation may assist in reducing stress and anxiety in people exposed to stressful conditions. However, longer-term and larger studies are needed to clinically justify its use as a therapeutic agent.

Participants:

People exposed to stressful conditions (from human trials reviewed)

Dosage:

200-400 mg/day

Study Quality Assessment:

Systematic review following PRISMA checklist, based on 9 peer-reviewed human randomised controlled trials where L-THE supplement was compared to a control. Acknowledges need for longer-term and larger cohort studies.

All Effects:

Participants:

healthy participants

Study Quality Assessment:

systematic review and meta-analysis of randomised controlled trials; meta-analysis performed using standardised mean differences (SMD)

Findings:

The main reported side effects of Camellia sinensis are hepatotoxicity and gastrointestinal disorders, especially when consumed on an empty stomach.