L-theanine is a water-soluble amino acid. Amino acids are the building blocks of proteins. L-theanine has been studied for its possible health benefits, ranging from cancer and stroke prevention to weight loss . However, most research on the amino acid has been conducted to assess its stress-relieving effects. 1
Optimal doses of tea or its constituents are not known.
L-theanine is thought to have both antioxidant and relaxant effects. 1 Some animal studies have shown that the amino acid may also be helpful in lowering lipids in the blood , fighting obesity, and preventing cognitive dysfunction and stroke. 1 L-theanine has been shown to increase the anti-tumor activity of two cancer-fighting drugs, doxorubicin and idarubicin . 2,3
Although there have been a handful of studies evaluating L-theanine for several conditions, 13 most research has been centered on its effects on mental status.
L-theanine has been shown to have a direct influence on brain activity, such as reducing stress. 4,12 At high doses (higher than usual doses found in a cup of black tea [20 mg (milligrams)]), it has the ability to relax the mind without causing drowsiness. One study measured a type of activity in the brain, called alpha activity, which plays an important role in attention. 5 Thirty-five participants were given either 50 mg of L-theanine or placebo. Electroencephalogram (EEG) tests were done at baseline and then at specified times afterwards (45, 60, 75, 90, and 105 minutes). Researchers found that there was a greater increase in alpha activity in those who took L-theanine compared to placebo, demonstrating that the amino acid had an effect on the participants’ general state of mental alertness and arousal.
A handful of studies have also looked at the combination of L-theanine and caffeine on various aspects of cognition and mood (eg, alertness, attention). 8,9,10,11 For instance, one study compared the effect of caffeine with and without L-theanine on cognition and mood in 27 participants. 10 Researchers gave participants placebo, caffeine, or caffeine plus L-theanine and measured their performance on several cognitive tests at baseline and then at 60 and 90 minutes after treatment. They found that the combination of caffeine and L-theanine improved speed and accuracy in an attention-switching task, as well as reduced the likelihood of distraction during a memory task. Caffeine alone did improve alertness and accuracy.
Researchers in Korea conducted a randomized, double-blind, placebo-controlled study to look at the effect of a LGNC-07, a combination of theanine and green tea extract, on memory and attention in 91 people with mild cognitive impairment. 6 Half of the participants were given 1,680 mg of LGNC-07 and the other half was given placebo for 16 weeks. Memory and word tests were conducted, as well as EEG tests. The researchers found that LGNC-07 improved memory and selective attention, as well as cognitive alertness.
Another small study also found the amino acid to have a positive effect in reducing anxiety . 7 The double-blind, randomized, placebo-controlled study was made up of 60 people diagnosed with schizophrenia or schizoaffective disorder . Of the 40 patients who completed the study, L-theanine was associated with reduced anxiety and was found to be well-tolerated and safe.
There have not been any side effects reported from taking L-theanine. However, drinking large amounts of green tea in general may cause upset stomach, irritability, and nausea due to the tea’s caffeine content. Also, do not take L-theanine if undergoing chemotherapy or are taking lipid-lowering medicines or sedatives, since L-theanine may alter the effects of these drugs.
1. L-theanine. Memorial Sloan-Kettering Cancer Center website. Available at: http://www.mskcc.org/mskcc/html/69285.cfm . Updated December 10, 2010. Accessed August 15, 2011.
6. Park SK, Jung IC, Lee WK, et al. A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study. J Med Food . 2011;14(4):334-343.
7. Ritsner MS, Miodownik C, Ratner Y, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. J Clin Psychiatry . 2011;72(1):34-42.
13. Miyagawa K, Hayashi Y, Kurihara S, Maeda A. Co-administration of l-cystine and l-theanine enhances efficacy of influenza vaccination in elderly persons: nutritional status-dependent immunogenicity. Geriatr Gerontol Int . 2008;8(4):243-250.
Last reviewed August 2013 by EBSCO CAM Review Board
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