L-theanine (L-THE) is a non-proteinogenic amino acid predominantly found in the leaves of the tea plant, Camelia sinensis, whose varieties produce green, white, oolong, black, aged Pu-erh, and ripened Pu-erh teas. The potential nootropic effects of L-THE, particularly for alleviating stress and anxiety and improving sleep quality, have seen an increase in its commercial application in products such as functional beverages and supplements despite the lack of conclusive evidence in the literature. The aim of this research project was to evaluate the effects of different concentrations of L-THE, in the form of a functional beverage sachet, on sleep and stress markers in individuals with mild to moderate sleep disturbances and determine an optimal concentration. In this randomised, double-blind, placebo-controlled, parallel-group, four-arm, dose response intervention trial, sixty healthy participants aged 18–65 with mild to moderate sleep disturbances were recruited to the study (UCHREC Approval Number: 2023–13247 and ACTRN12623000776606; Universal Trial Number (UTN) is U1111–1292-0328). Enrolled participants were randomly allocated to one of four treatment arms (100mg L-THE, 200mg L-THE, 400mg L-THE or placebo) in a 1:1:1:1 ratio, where they consumed a functional beverage for 14-days following a 7-day baseline period. The primary outcomes of this study were changes from baseline in objective and subjective sleep quality parameters alongside changes in secondary outcome measures of biochemical, physiological, and subjective stress markers relative to baseline. This clinical trial is the first to comprehensively evaluate the effectiveness (optimal dose) of L-THE at improving sleep quality and stress markers using a suite of objective, subjective, physiological, and biochemical tools.
Bulman et al. (Wed,) studied this question.