ABSTRACT
L-Theanine is a distinctive non-protein amino acid prevalent in tea leaves. Recent interest in its possible application as a dietary supplement has increased, particularly about assertions related to facilitating relaxation and enhancing cognition. This review examines the chemical, metabolism, and alleged biological activity of l-theanine. It is efficiently absorbed from the gut and can traverse the blood-brain barrier. Certain studies indicate that l-theanine may enhance alpha wave activity in the brain, which is linked to relaxing and focused attention, alleviate stress and anxiety, and improve sleep quality, however results are frequently uneven. Animal models have also demonstrated potential neuroprotective and anti-seizure benefits. The combination of coffee and l-theanine may enhance cognitive function, alertness, and concentration. Nevertheless, the data substantiating several health claims is still inadequate, particularly due to the absence of stringent human clinical studies. Although l-theanine demonstrates a favorable safety profile according to toxicological research, prudence is advised concerning its alleged health advantages until more robust scientific evidence is established. The mechanisms of action and therapeutic potential of l-theanine necessitate additional exploration, considering the growing interest and popularity of this nutraceutical supplement promoted for cognitive health and relaxation. In the absence of rigorously designed and meticulously controlled human clinical trials, we advise caution regarding the use of l-theanine supplements at pharmacological doses by the general populace, asserting that the scientific evidence does not yet substantiate the enthusiasm surrounding this popular supplement for cognitive health and relaxation.
AUTHORS:
Roderick Dashwood, Department of Translational Medical Sciences, Texas A&M University Naresh K. Vashisht College of Medicine, and Center for Epigenetics & Disease Prevention, Texas A&M Health, Houston, Texas, USA.
Francesco Visioli, Department of Molecular Medicine, University of Padova, Padova, Italy.
Publisher: Nutrition Research
Citation: Dashwood, R., & Visioli, F. (2025). L-theanine: From Tea Leaf to trending supplement – does the science match the hype for Brain Health and relaxation? Nutrition Research, 134, 39–48. https://doi.org/10.1016/j.nutres.2024.12.008