Plain language summary
The beneficial effects of green tea and its components are well known. The ingredient L-Theanine is the most abundant water soluble non-proteinous amino acid component in green tea. The second most abundant ingredient is L-Arginine. It also exhibits a high stress-reducing effect. The hypothesis of this study was that the combined ingestion of L-arginine and L-theanine could have beneficial clinical effects for psychological stress compared with ingestion of theanine alone. This study was a randomised placebo-controlled, single-blinded study in healthy young adults. Participants (n=120) were randomly assigned to one of the three groups (1:1:1); L-theanine alone, L-theanine and L-arginine or placebo. Results show that combined ingestion of L-theanine and L-arginine tended to have greater stress reducing effects than ingestion of L-theanine alone. However, the difference was not statistically significant. Authors conclude that their findings are suggestive of synergistic effects of L-theanine and L-arginine against stress in young adults.
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-controlled 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 theanine/arginine (200 mg l-theanine, 50 mg l-arginine), or placebo groups. After consuming 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 -2.75 (11.2) kIU/L in the theanine/arginine group, -0.40 (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 (p=0.007) and theanine (p=0.02) groups differed significantly from those in the placebo group. However, the difference between theanine/arginine and theanine groups, was not statistically significant (p=0.74). 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.
Methodological quality
Jadad score
:
3
Allocation concealment
:
Yes
