In a 2016 published study, researchers evaluated the anti-stress, cognitive and neurophysiological effects of L-theanine in healthy adults. They found this amino acid was effective at reducing stress levels after various cognitive stress tests.
In a double-blind, placebo-controlled, balanced crossover model, researchers measured stress, fatigue, mood and salivary cortisol production in 34 adults aged 18-40 years, following three multitask cognitive stressor tests. Testing was completed pre-treatment, and one and three hours after giving 200mg of an L-theanine-based nutrient drink. Brain alpha activity, related to relaxation, was also evaluated in a subset group.
The results were time dependent with a significant decrease in subjective stress one hour after taking L-theanine, but with no difference at three hours. However, salivary cortisol was no different at one hour but was significantly lower three hours later. The researchers state the difference in response may be due to the timing of saliva sampling, or to a delay between HPA axis activation and the subsequent change in saliva concentration. Additionally, stress reduction was specifically linked to the cognitive stress testing, not with the level of stress or general mood prior to the start of the study.
Resting state alpha brain waves were significantly higher but only in those participants with moderate to high levels of anxiety tendencies. Fatigue and anxiety were reduced, while alertness, calmness and cognitive function increased, but none of these were at a statistically significant level, compared to the placebo.
L-theanine is an amino acid chemically similar in structure to the excitatory neurotransmitter glutamate. It has the ability to cross the blood brain barrier and to bind, with low affinity, to glutamate receptors.
Animal studies show the possible effectiveness of L-theanine in stress and mood disorders may be due to its ability to:
- inhibit glutamate
- increase GABA, dopamine and glycine
- modulate serotonin levels
- increase brain-derived neurotrophic (BDNF) expression.
This study supports previous research into the anti-stress effects of L-theanine. However, the product used contained very small amounts of phosphatidylserine, alpha glycerylphosphorylcholine (GPC) and chamomile. The authors state that future studies with only L-theanine would be beneficial to determine if these ingredients had any effect on the outcome.
1. White DJ, de Klerk S, Woods W, et al. Anti-stress, behavioural and magnetoencephalography effects of an L-theanine-based nutrient drink: a randomised, double-blind, placebo-controlled, crossover trial. Nutrients 2016;8(1):53. [Full Text]