L-Theanine is an amino acid found in tea and is one of the reasons for the beneficial effects of green tea.
Research has shown that daily doses ranging from 200 to 400 mg of L-Theanine produced anti-stress effects (Sakamoto FL, et al., 2019).
When a mental arithmetic task was used as an acute stressor, L-Theanine intake resulted in a reduction of the heart rate and salivary immunoglobulin A responses to the acute stress task when compared to the placebo. ( (Kimura K, et al., 2007).
The analyses of heart rate variability indicated that the reduction of the stress response was likely caused by a reduction of the sympathetic nervous activation.
The following research was a randomized, placebo-controlled, crossover, double-blinded study (Hidese S, et al., 2019). Cognitive functions, verbal fluency, and executive function scores improved after L-theanine administration when compared with the placebo treatment.
200mg of L-Theanine was found to improve sleep quality in this study (Rao TP, et al., 2015).
L-theanine provided protection of nerve cells when exposed to certain toxins in cell culture (Cho HS, et al., 2008).
Hong-Suk Cho 1, Seung Kim, Sook-Young Lee, Jeong Ae Park, Sung-Jun Kim, Hong Sung Chun, Protective effect of the green tea component, L-theanine on environmental toxins-induced neuronal cell death, Neurotoxicology, 2008 Jul;29(4):656-62.
Hidese S, Ogawa S, Ota M, Ishida I, Yaskawa Z, Ozeki M, Kunugi H. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.Nutrients. 2019 Oct 3;11(10):2362.
Kimura K, Ozeki M, Juneja LR, Ohira H.L-Theanine reduces psychological and physiological stress responses.Biol Psychol. 2007 Jan;74(1):39-45.
Lopes Sakamoto F, Metzker Pereira Ribeiro R, Amador Bueno A, Oliveira Santos H. Psychotropic effects of L-theanine and its clinical properties: From the management of anxiety and stress to a potential use in schizophrenia. Pharmacol Res. 2019 Sep;147:104395
Rao TP, Ozeki M, Juneja LR. In Search of a Safe Natural Sleep Aid. J Am Coll Nutr. 2015;34(5):436-47.