Effect of Combined Ingestion of l-Theanine and l-Arginine for Short-Term Psychological Stress in Young Adults: A Randomized Placebo-Controlled Study

Abstract

l-Theanine, the most abundant amino acid component in green tea, has anti-stress effects and refreshes the mental state. A recent study demonstrated that l-arginine, the second most abundant amino acid in green tea, might enhance the anti-stress effects of l-theanine. The aim of this study was to evaluated the effects of combined ingestion of l-theanine and l-arginine on psychological stress in humans. A randomized placebo-con-trolled trial was conducted including 120 healthy young adults (mean age 22.4 y, 63.3% female). Subjects were randomly assigned to theanine (200 mg l-theanine), combined the-anine/arginine (200 mg l-theanine, 50 mg l-arginine), or placebo groups. After consum-ing a test beverage, we administered a stress-loading test (Uchida-Kraepelin performance test) and performed salivary alpha-amylase activity (sAA) measurements to assess the physiological stress response at 0 min (immediately after), 5 min, and 15 min. The changes in sAA at 15 min after the stress-loading test were 22.75 (11.2) kIU/L in the theanine/argi-nine group, 20.40 (11.5) kIU/L in the theanine group, and 6.95 (18.6) kIU/L in the placebo group. The values in the theanine/arginine (p50.007) and theanine (p50.02) groups differed significantly from those in the placebo group. However, the difference between the-anine/arginine and theanine groups, was not statistically significant (p50.74). From this study, no clear conclusion could be drawn regarding the potentiating effect of theanine and arginine combined ingestion on anti-stress effects in human.