Do you want to be relaxed? That's the promise of drinking tea whose leaves are enriched with GABA. The result is said to be improved sleep and an anti-stress effect. But on what studies are these claims based?
The cultivation of GABA-enriched tea was developed in Japan in the 1980s (1). It was in response to a scientific study on tea consumption to reduce high blood pressure. GABA is a molecule known to block hypertension and is naturally synthesized by the leaves of tea plants. The researchers of this study have therefore developed this method of cultivation to obtain leaves with antihypertensive potential (2)
GABA what?
Behind this acronym lies γ-aminobutyric acid. It is a chemical compound called neurotransmitter that regulates the functioning of the nervous system. In this case, GABA reduces the activity of certain areas of the brain, such as the limbic system, which regulates emotions, or the sleep circuit, which depends on different areas of the brain. Certain nerve endings that bind GABA can cause blood vessels to dilate, which is a reduction in high blood pressure.
The neurons, which generate nervous information, project fibers that allow the conduction of nervous messages. A bit like an electric cable, these fibers isolate the message for its proper propagation to the nerve ending. Between the nerve ending and its target, there is the synapse. It is an empty zone where the secretion of neurotransmitters, ordered by the message being propagated, will take place.
In the case of a relaxation signal, GABA will be secreted into the synapse and will bind to receptors on the surface of the target area to be relaxed: these are GABAergic receptors. These receptors open channels for the entry of negatively charged molecules, chloride ions. The consequence will be a blockage of the nervous signal at this level: the target zone is no longer active.
And the GABA in tea leaves, how is it produced?
GABA is made from an amino acid, glutamic acid, which is a constituent of proteins. The synthesis of GABA also requires nitrogen (79% of the earth's atmosphere). The leaves of tea plants naturally produce GABA. By replacing oxygen with nitrogen in tea plants, the leaves produce much more GABA.
GABA tea, the key to attracting the sandman?
Wakefulness and sleep are regulated by many structures in the brain. They are connected to each other. Sleep is divided into several phases (3): falling asleep (slowing down of the activity of the cerebral cortex), slow wave sleep (loss of perception of what surrounds us) and REM sleep (the phase of total rest). These phases are repeated several times a night. Without falling asleep and maintaining slow wave sleep, there is no REM sleep: this is insomnia.
GABA can bind to the GABAergic receptors of the sleep system. This will block the messages sent to maintain wakefulness. The sleep system will no longer be activated, brain activity decreases: this is sleepiness. This blocking by GABA continues during slow wave sleep until the beginning of REM sleep (4)
The first study of the impact of daily consumption of oolong GABA on the quality of sleep in humans was conducted in 2009 (5). This first observation was made in a single 42-year-old patient with signs of insomnia. By consuming 250mL of oolong GABA per night for 20 weeks, Dr. Tsai reported that the patient fell asleep in 2min versus 9min, with longer slow wave sleep maintenance and reduced periods of spontaneous wakefulness. Interestingly, when the patient stopped the GABA oolong and consumed green tea, this improvement in sleep decreased, showing the impact of drinking this type of tea. These initial results are in line with those of a more recent study in mice with sleep disorders who consumed 3g of black GABA tea powder diluted in 500mL of water heated to 100°C (6)
If one can be tempted to conclude that there are clear effects on sleep, it is necessary to continue these tests on larger groups of individuals to conclude that there is a potential beneficial effect.
GABA tea, the sunshine of the brain?
Anxiety and depression are emotional states controlled by the limbic brain system. It is a number of interconnected structures that regulate the emotions of an individual. In the case of chronic and acute stress (depression) or potentially stressful situations (anxiety), these structures are active all the time. The limbic system is no longer controlled and leads to emotional upheaval. In the limbic system, there are GABAergic receptors that can bind GABA. If GABA binds to these receptors, the structures are no longer activated and may reduce some of the symptoms associated with depression and stress (7)
A recent cohort was conducted on 30 university students with chronic stress. Two groups of students consumed either 5g of GABA oolong or 5g of classic oolong, infused for 10min at 90°C. To assess the stress, the authors measured the students' heart rate variations. A continuous variation in heart rate is a sign of chronic stress. These measurements were taken at the arrival of the students and 30min after drinking the tea. These measurements revealed that the heart rate variations were more stable after consumption of GABA oolong, which may reflect a potential reduction in stress (8).
Nevertheless, these students also answered a questionnaire on their general stress state, no improvement was noted after consumption of GABA oolong.
A clinical study was also conducted on the daily consumption of 300mL of 3.5g of GABA oolong infused at 100°C for 2min by 9 children with autism spectrum symptoms. Stress is associated with the level of cortisol collected at waking and during the day. Cortisol is a hormone produced in very large quantities when under stress. Here, the majority of the children had decreased cortisol levels, potentially a decreased stress (9)
However, this remains a biological parameter that does not reflect the psychological state of an individual caused by chronic stress.
While these initial results seem to demonstrate possible relaxing effects of GABA tea in animals and humans, more studies are needed to fully understand how GABA tea works and to scientifically validate these preliminary results. The research on GABA tea is still a fertile ground on which beautiful studies can grow.