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L-Theanine Studies

This list of L-theanine studies will help you to determine whether it is an effective compound for you. Whether it is as an anxiety treatment or to improve your sleep, you will find L-theanine sublingual solution to be an incredibly effective method.

Original article:
Ai Yoto*, Mao Motoki, Sato Murao and Hidehiko Yokogoshi. (2012), Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. Journal of Physiological Anthropology, 31; 28.

In this study, the effects of orally administered L-theanine or caffeine on a human subject’s mental performance, mood, and physiological response (specifically blood pressure and skin temperature) to psychological and physical stress were compared. While caffeine and L-theanine have been shown to have beneficial effects on cognition and mood, their effects on a subject’s physiological response to stress have not been compared. This study was conducted to do so.

Sixteen volunteers (eight men and eight women in their early twenties) were each tested at similar times on three separate days, each seven days apart. The volunteer completed a profile of mood states (POMS) and was assessed using the visual analogue scales (VAS) for subjective ratings on mood state before intake. One minute was used to obtain baseline data for the subject’s blood pressure and skin temperature. 200 mg of L-theanine, 100 mg of caffeine, or a placebo were then orally administered in the form of a capsule.

The subject was then tested in two rounds of tests, each consisting of an auditory target detection task and an arithmetic mental task. During the tests, the subject’s blood pressure and skin temperature were recorded at regular intervals. After the mental tests, POMS and VAS were completed again, followed by an additional minute for recording blood pressure and skin temperature.

The subject then completed a cold pressor test in which the subject’s hand was immersed in ice water for one minute and then placed on a towel for a three-minute recovery period. During this test, the subject’s blood pressure and skin temperature were again recorded at regular intervals. After all tests, VAS about the subject’s feelings of each test was completed.

Results of the tests showed the subject’s skin temperature was not affected by the substance administered. While the subject answered more questions during the mental arithmetic task after treatment of both L-theanine and caffeine, the accuracy of the answers was not affected. POMS results showed subjects treated with L-theanine experienced lower levels of tension-anxiety caused by the psychological stress of the mental tests than those treated with a placebo or caffeine.

Treatment with L-theanine was shown to significantly reduce a rise in blood pressure due to psychological stress in subjects at possible risk of hypertension. Neither L-theanine nor caffeine was shown to decrease the rise in blood pressure due to physical stress caused by the cold pressor test.

Original article:
Shigekazu Kurihara, Takenori Hiraoka, Masahisa Akutsu, Eiji Sukegawa, Makoto Bannai, and Susumu Shibahara. (2010), Effects of L-Cystine and L-Theanine Supplementation on the Common Cold: A Randomized, Double-Blind, and Placebo-Controlled Trial. Journal of Amino Acids, 2010; 307475.

Conventional treatments for the common cold are limited to medications that only alleviate the symptoms of the virus. Many antiviral medications are reserved for preventing influenza. However, there have been previous studies that have shown that oral ingestion of L-cystine and L-theanine increase production of antibodies in mice. The purpose of this study was to investigate the ability of L-cystine and L-theanine to prevent the common cold and alleviate its symptoms in human subjects.

A total of 176 men, all of unspecified age, took place in the study. They were randomly sorted in either the treatment or the placebo group. Over a 5 week period during January and February of 2002 (a peak time for contractions of the common cold), each subject was instructed to take two tablets of either a mixture of L-cystine and L-theamine or a placebo both after breakfast and dinner.

The daily dosage of L-cystine, L-theanine, and glycine (the placebo) were 700 mg, 280 mg, and 980 mg, respectively. Over the study period, the subject performed a daily self-evaluation of the presence and severity of 19 symptoms associated with the common cold. Using the data collected, the researchers determined how many separate cases of the common cold each subject experienced and compared the data of the group treated with L-cystine and L-theamine with that of the group that took the placebo.

Results from the study showed that subjects treated with L-cystine and L-theamine experienced a significantly lower number of cases of the common cold and experienced a lower severity of symptoms associated with the virus compared to the group that took the placebo.

The treated group experienced approximately 58% less cases of the common cold. While the average duration of the colds experienced by the treated group were 10% shorter than those of the placebo group, this result was determined to be statistically insignificant.

The only adverse effect of the L-cystine and L-theanine treatment was a 14.8% occurrence of diarrhea. However, subjects treated with the placebo experienced a 15.3% occurrence of diarrhea. These findings suggest that treatment with L-cystine and L-theanine may be effective in preventing the onset of the common cold.

Original Article:
Takami Kakuda, Hisato Yanase, Kazuhiro Utsunomiya, Ayumu Nozawa, Tomonori Unno, Kiyoshi Kataoka. (2000), Protective effect of g-glutamylethylamide (theanine) on ischemic delayed neuronal death in gerbils. Neuroscience Letters, 289; 189-192.

In elderly persons, cases of dementia have been shown to correlate with ischemic neuronal death, which is the death of brain cells caused by the obstruction of blood vessels leading to the brain. When blood flow to the brain is restricted, a spike in the concentration of glutamate (a neurotransmitter) in the brain causes a large influx of calcium ions, leading to neuronal death.

Previous research has shown that treatment with glutamate antagonists before ischemia decreases the rate of neuronal death. L-theanine has also been shown to prevent glutamate induced neuronal death in rat neuron cultures. This study was conducted to examine the effectiveness of treatment with L-theanine in preventing ischemic neuronal death in gerbil test subjects.

In the study, four test groups of gerbils were examined. One group was administered a saline placebo before the induced ischemia. The second group was administered 1 μL solutions of L-theanine in concentrations of either 50, 125, or 500 μM before the operation. The third group was administered 1 μL of 500 μM L-theanine 30 minutes after the ischemia. A final control group was administered 1 μL of 500 μM L-theanine but did not undergo ischemia.

The treatment was administered by slowly injecting the solution in the lateral ventricle of the subject’s brain over a period of 20 minutes. Ischemia was induced by obstruction of the subject’s two common carotid arteries for three minutes. After seven days of survival, the subject’s brain was recovered and examined. The number of intact neurons in a 500 by 100 μm section of the hippocampus cut 4 μm thick were counted and recorded. Throughout the study, the subject’s brain temperature was monitored.

Results showed that the group treated after the ischemia experienced the same level of neuronal death as the placebo group. However, subjects treated with L-theanine before the ischemia experienced significantly lower levels of neuronal death. The effectiveness of treatment was found to be dependent on the dose of L-theanine given, with higher doses more effective at preventing neuronal damage or death.

Subjects treated with the 500 μM dose were found to have 90% of their neurons survive. These findings suggest that L-theanine may be an effective neuroprotective agent, as it is also water soluble and able to pass through the blood-brain barrier. Brain temperature data recorded during the study showed that the neuroprotective effect of L-theanine did not depend on decreasing the brain’s temperature like other neuroprotective chemicals do.

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