This was the main conclusion of a study published in Nutrients by a team of researchers from the University of Shizuoka in Japan.
The double-blind crossover study compared the stress responses and sleep parameters of 20 middle-aged workers drinking reduced-caffeine and standard green tea.
Stress levels were measured looking at salivary alpha-amylase activity (sAA) – an oral cavity enzyme considered a stress marker – and sleep parameters measured with a single-channel electroencephalogram (EEF). Subjective stress and fatigue were also considered.
“The level of sAA, a marker of stress, was significantly lower in the participants that consumed low-caffeine green tea than standard green tea. Furthermore, ingestion of low-caffeine green tea significantly improved sleep quality and reduced subjective fatigue on Monday morning.
“These results suggest that a reduction of caffeine in green tea is beneficial for reducing stress,” the researchers wrote.
A delicate balance - more space to theanine
The researchers said the theanine in green tea – an amino acid found in the leaves – was associated with “significant anti-stress effects in animals and humans”.
The ingredient worked in the brain to reduce levels of excitatory neurotransmitters and enhance levels of the main inhibitory neurotransmitter, striking an important balance, they said.
By reducing caffeine in green tea (to between one-quarter and one-fifth of standard green tea), the naturally occurring theanine gained more prominence. Levels were 1.2 times higher than in standard green tea with component ratios going from 1:1:0.5 (theanine, caffeine and epigallocatechin gallate (EGCG)) to 1:0.3:0.3 in reduced-caffeine tea.
This, they said, gave space for the theanine to work more significantly but more research had to be done, specifically into the role other components played in anti-stress.
Future research should specifically find the “mechanism of action of the stress-reducing effect of green tea components”.
Method and findings – the specifics
Prior to the trial, all participants were asked to have a ‘wash out’ week, drinking just water. Participants were then asked to prepare their tea in a water bottle each morning using a 3g teabag and 500ml of room temperature water and drink it throughout the day until evening. All were encouraged to avoid other high-caffeine beverages.
The current study indicated that mean sAA levels after work – self-measured by each participant – were “significantly lower” when participants consumed low-caffeine green tea (p= 0.043). Levels before work also “tended to be lower” (p= 0.109), the researchers said.
Sleep parameter results showed little difference in many measurements, but participants drinking low-caffeine green tea had a shorter early morning awakening time (B2 WASO) and also a “significantly higher” ratio of non-REM sleep – a marker of deep sleep.
This suggested, therefore, that “increased theanine intake may increase sleep quality”, the researchers said.
Subjective stress also “tended to be lower” when participants drank the low-caffeine green tea (p=0.152) and accumulated fatigue felt on Monday morning was “significantly lower” (p=0.015).
Source: Journal Nutrients
Published online July 19, 2017 – doi: 10.3390/nu9070777
“Reduced stress and improved sleep quality caused by green tea are associated with a reduced caffeine content”
Authors: K. Unno et al.