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

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.

Antidepressant Effect of Shaded White Leaf Tea Containing High Levels of Caffeine and Amino Acids.

The young leaves of green tea become lighter in color than usual when protected from sunlight by a shading net for about two weeks while growing. These leaves are called "shaded white leaf tea" or SWLT. In the eluate of SWLT, the amount of amino acids (361 mg/L) was significantly higher than that in regular tea (53.5 mg/L). Since theanine and arginine, the first and second most abundant amino acids in SWLT, have significant antistress effects, we examined the antistress effect of SWLT on humans. SWLT or placebo green tea (3 g) was eluted with room-temperature water (500 mL). Participants consumed the tea for one week prior to pharmacy practice and continued for 10 days in the practice period. The state-trait anxiety inventory, an anxiety questionnaire, tended to be scored lower in the SWLT group than the placebo, but other stress markers showed no differences. The effect of the difference in SWLT components examined with mice showed that aspartic acid and asparagine, which are abundant in SWLT, counteracted the antistress effects of theanine and arginine. Large amounts of caffeine also interfered with SWLT's antistress effect. Thus, SWLT, which is high in caffeine and amino acids, suppressed depressant behavior in mice.