L-Theanine
Uses
Alternate Names/Related Terms
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
Sources
L-theanine is found mainly in tea (eg,
green tea
and
black tea
), and to a less extent in mushrooms. L-theanine is also available in its purified form as an oral dietary supplement.
1
Therapeutic Dosages
Optimal doses of tea or its constituents are not known.
Therapeutic Uses
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
What Is the Scientific Evidence for L-Theanine?
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 L-theanine on memory and attention in 91 people with mild cognitive impairment.
6
Half of the participants were given 1,680 mg of L-theanine (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 L-theanine 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.
Safety Issues
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.
References
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.
2
Sugiyama T, Sadzuka Y. Combination of L-theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma.
Clin Cancer Res
. 1999;5(2):413-416.
3
Sadzuka Y, Sugiyama T, Sonobe T. Improvement of idarubicin induced antitumor activity and bone marrow suppression by L-theanine, a component of tea.
Cancer Lett
. 2000;158(2):119-124.
4
Juneja LR. Suntheanine and its relaxation effect in humans.
Trends in Food Science & Tech
. 1999;10;199-204.
5
Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state.
Asia Pac J Clin Nutr
. 2008;17 Suppl 1:167-168.
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.
8
Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.
Nutr Neurosci
. 2010;13(6):283-290.
9
Einöther SJ, Martens VE, Rycroft JA, De Bruin EA. L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness.
Appetite
. 2010;54(2):406-409.
10
Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood.
Nutr Neurosci
. 2008;11(4):193-198.
11
Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine, and their combination on cognition and mood.
Biol Psychol
. 2008;77(2):113-122.
12
Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses.
Biol Psychol
. 2007;74(1):39-45.
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.