How It Works
Bottom Line: L-theanine has been studied in animals as an adjuvant cancer treatment. No such studies have been conducted in humans.
L-theanine is an amino acid found in
green tea. Laboratory and animal studies showed that L-theanine increases efficiency of chemo drugs and also reduces side effects from use of such drugs. One epidemiological study showed that green tea reduced the incidence of stroke in individuals who consumed green tea. However, it is unclear if L-theanine contributed to this benefit. No clinical trials on L-theanine have been conducted.
Purported Uses
Relaxant
Animal studies have shown that L-theanine has relaxant properties but it does not reduce anxiety.
Cancer prevention
There is no scientific evidence to substantiate this use.
Cancer treatment
Laboratory and animal studies indicate that L-theanine has antitumor properties but human data is lacking.
Stroke
Results from a study done in Japan suggest that green tea consumption decreased the risk of stroke in individuals. However, it is unclear if L-theanine contributed to this benefit
Research Evidence
An epidemiological study showed that increased consumption of green tea (which contains L-theanine) reduced the incidence of stroke.
Warnings
Although there are no reported side effects from taking L-theanine, consumption of large amount of green tea can cause nausea, irritability, and GI upset because of the caffeine content.
Do Not Take If
You take chemotherapeutic drugs because L-theanine can increase their effects
You take sedatives as L-theanine can have additive effects
You take lipid lowering drugs as L-theanine can increase their effects
Side Effects
Common Name
Theanine, gamma-glutamylethylamide
Clinical Summary
L-theanine is a water soluble amino acid found in
green tea and in mushrooms. Purified L-theanine is available as an oral dietary supplement. It is consumed for its perceived antioxidant and relaxant effects
(12). Several in vitro and animal studies have shown that L-theanine has lipid lowering
(1), neuroprotective
(2), anti-obesity
(3) and antitumor
(1) properties. It was also shown to affect levels of some neurotransmitters in rats
(10) (11). In addition, L-theanine enhanced the chemotherapeutic effects of doxorubicin
(5) and idarubicin
(6) and also alleviated the adverse effects from use of these agents in vitro
(7). Data from an epidemiological study suggest beneficial effects of L-theanine for prevention of stroke
(4) but it has not been subjected to clinical trials.
Food Sources
Camellia sinensis, the source of green tea
Purported uses
- Cancer prevention
- Cancer treatment
- Relaxation
- Stroke
Mechanism of Action
L-theanine is thought to increase the antitumor activity of chemotherapeutic drugs, doxorubicin and idarubicin (5) (6). These agents normally bind the glutamate receptor and the complex is transported across the cell resulting in reduced concentrations and hence attenuated effects of these drugs. L-theanine competes with chemo drugs for binding the glutamate receptor and prevents their efflux. It was also shown to affect levels of dopamine and serotonin in animals (10) (11). The neuroprotective effects of L-theanine are also thought to be due to its selective binding to glutamate receptors (2). L-theanine does not induce or inhibit cytochrome P450 enzymes (9).
Pharmacokinetics
Studies in rats have demonstrated that it is absorbed into plasma and tissues, and reaches a maximum level at 0.5 - 2 hrs following oral absorption. It is believed that L-theanine is hydrolyzed in the kidneys to glutamic acid and ethylamine by phophate-independent glutaminase. The byproducts are eliminated from the body within 24 hrs
(2) (8).
Warnings
Although there are no reported side effects from taking L-theanine, consumption of large amount of green tea can cause nausea, irritability, and GI upset because of the caffeine content.
Contraindications
Hypersensitivity to green tea
Pregnancy and lactation
Chemotherapeutic drugs
Lipid lowering drugs
Sedatives
Adverse Reactions
Herb-Drug Interactions
Chemotherapeutic drugs: Although not demonstrated in humans, L-theanine may potentiate the effects of chemotherapeutic drugs
Lipid lowering drugs: L-theanine may have additive effects
Sedatives: L-theanine may increase the effects of sedatives
Literature Summary and Critique
Data from in vitro and animal studies suggest that L-theanine has beneficial effects but clinical trials have not been conducted so far.
References
- Zhang G, Miura Y, Yagasaki K. Effects of dietary powdered green tea and L-theanine on tumor growth and endogenous hyperlipidemia in hepatoma-bearing rats. Biosci Biotechnol Biochem. 2002; 66(4):711-6.
- Kakuda T. Neuroprotective effects of the green tea components L-theanine and catechins. Biol Pharm Bull. 2002; 25(12):1513-8.
- Zheng G, Sayama K, Okubo T, Juneja LR, Oguni I. Anti-obesity effects of three major components of green tea, catechins, caffeine and L-theanine, in mice. In Vivo. 2004;18(1):55-62.
- Sato Y, Nakatsuka H, Watanabe T, Hisamichi S, Shimizu H, Fujisaku S, et al. Possible contribution of green tea drinking habits to the prevention of stroke. Tohoku J Exp Med. 1989; 157(4):337-43.
- Sugiyama T, Sadzuka Y. Combination of L-theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res. 1999; 5(2):413-6.
- 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):119-24.
- Sugiyama T, Sadzuka Y. L-theanine, a specific glutamate derivative in green tea, reduces the adverse reactions of doxorubicin by changing the glutathione level. Cancer Lett. 2004;212(2):177-84.
- Tsuge H, Sano S, Hayakawa T, Kakuda T, Unno. T. L-theanine, gamma-glutamylethylamide, is metabolized by renal phosphate-independent glutaminase. Biochim Biophys Acta. 2003;1620(1-3):47-53.
- Sadzuka Y, et al. Efficacy of theanine is connected with theanine metabolism by any enzyme, not only drug metabolizing enzymes. Food Chem Toxicol 2006; 44(2):286-92.
- Yokogoshi H, et al. Theanine-induced reduction of brain serotonin concentration in rats. Biosci Biotechnol Biochem 1998; 62(4): 816-17.
- Yokogoshi H, et al. Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats. Neurochem Res 1998; 23(5): 667-73.
- Lu K, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol Clin Exp 2004: 19: 457-65.
