On the other hand, caffeine absorption from the gastrointestinal tract is rapid and reaches 99% in about 45 min after ingestion, while peak plasma caffeine concentration is reached between 15 min and 120 min, and half-life ranges from 2.5 h to 4.5 h after oral ingestion in humans also reported that L-theanine could influence the secretion and function of neurotransmitters in the central nervous system even at 30 min after oral administration ![]() reported that L-theanine plasma concentration reached the peak between 32 and 50 min after oral ingestion, and its half-life ranged from 58 min to 74 min in humans reported that L-theanine increased by 1 h at the latest in the serum, the liver, and the brain after administration, and thereafter decreased sharply in the serum and liver ![]() Treatments were allocated using a Latin square design such that the order of treatments was counterbalanced across participants. All sample capsules were taken with 250 mL warm water at about 25☌. Dextrin (Nisshin Pharma Inc., Tokyo, Japan) was used as the placebo. In total, three separate trials were performed, in which the participants orally took either L-theanine (200 mg, Taiyo Kagaku Co., Tokyo, Japan) + placebo, caffeine (100 mg, Shiratori Pharmaceutical Co., Chiba, Japan) + placebo, or placebo only on each day. In this study, we investigated the effects of L-theanine or caffeine on mental task performance and the change in blood pressure caused by mental tasks as psychological stress and by the cold pressor test as physical stress.Ī cross-over, randomized, placebo-controlled design was used in this study. , but no study has compared these two components under conditions in which acute psychological and physical stresses increase blood pressure. On the other hand, both caffeine and L-theanine were recently found to have beneficial effects on cognition and mood ![]() Adenosine antagonism has been implicated as a contributor to the direct cardio-acceleratory effect of caffeine, which also increased blood pressure and respiration rate Caffeine is a CNS-stimulating drug that acts as an adenosine receptor antagonist in the brain From these findings, it can be hypothesized that L-theanine attenuates the stress responses in the autonomic nervous system induced by both physically and psychologically stressful tasks.Ĭaffeine, another major component of green tea, also has behavioral effects on autonomic nervous activities, and these effects are thought to be the opposite those of L-theanine. , L-theanine may have inhibited the increase in blood pressure through its anti-stress effects on the autonomic nervous system. ![]() It is known that stress can elevate blood pressure by stimulating the nervous system to produce large amounts of vasoconstricting hormones that increase blood pressure Moreover, animal studies have found that L-theanine reduced blood pressure in hypertensive rats Kimura (2007) reported that L-theanine intake reduced heart rate and salivary immunoglobulin A responses to an acute stress task (an arithmetic task), suggesting that L-theanine could reduce stress by inhibiting cortical neuron excitation Several reports have found increased alpha brain wave activity in humans after L-theanine administration, indicating that L-theanine could lead to a relaxed and alert state Animal studies have revealed that L-theanine affected dopamine and serotonin concentrations in the brain, underlying its anxiolytic effect L-theanine became one of those popular items since its multiple roles in the central and autonomic nervous systems received attention. To live a healthier life in so-called high-stress modern society, a growing interest in natural, minimally processed, nutritional, and healthy foods is spreading around the world, and many kinds of functional food ingredients have recently become widely used due to their health benefits.
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