L-theanine is an amino acid predominantly found in green tea leaves that has been shown to ease stress and help promote relaxation.
Rich in antioxidants, L-theanine is also being researched for its lipid-lowering, neuroprotective, anti-obesity and antitumor properties (1).
L-theanine may increase the antitumor activity of chemotherapeutic drugs. Several laboratory and animal studies show that L-theanine increases the efficiency of certain chemotherapy drugs and also reduces their side effects.
In one animal study, the effect of combining theanine with the chemotherapy drug, doxorubicin increased not only the antitumor activity of the primary ovarian tumor, but also helped prevent the cancer from metastasizing (spreading to other parts of the body).
In another study, the combination of theanine and the chemotherapy drug, idarubicin resulted in significant antitumor activity in mice with leukemia.
Further results showed that theanine helps improve toxicities that may come with use of the chemotherapy drug (2).
Researchers stress that patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because these effects have not yet been studied in human clinical trials.
L-theanine promotes relaxation. A cup of hot tea has long been the drink of choice of those seeking a beverage that soothes and relaxes. Researchers have pinpointed L-theanine as the compound partly responsible for the beverage’s impact on mood.
The compound promotes relaxation by contributing to a number of changes in the brain. These include boosting neurotransmitters (serotonin and dopamine) that work in the brain to regulate emotions, mood, concentration, alertness, and sleep, as well as appetite, energy and other cognitive skills; reducing levels of chemicals in the brain that are linked to stress and anxiety; and enhancing alpha brain waves which are associated with a state of “wakeful relaxation.” (3)
One of the perks of L-theanine is that it works to relax without sedating, which makes it a great alternative for those looking for a supplement that helps them unwind, without worrying about becoming sleepy during the day.
L-theanine provides stress relief.
In a recent study, 18 university students were divided into one of two groups: a high anxiety propensity group and the minimal anxiety propensity group. Both groups received l-theanine (200 mg/100 ml water) and placebo (100 ml water) in a double-blind repeated measurement design protocol.
Results revealed that only those with high baseline anxiety noted benefits associated with relaxation whereas those who were not anxious fail to outperform placebo (4).
L-theanine may help treat symptoms of schizophrenia. In a 2011 issue of The Journal of Clinical Psychiatry, researchers discussed the efficacy of L-theanine on patients with schizophrenia or schizoaffective disorder.
Compared with placebo, supplementation of 400 mg/d of L-theanine added to ongoing antipsychotic treatment was able to significantly reduce positive and general psychopathology symptoms and anxiety. Supplementation was found to be a safe and well-tolerated (5).
Further long-term studies of L-theanine are needed to substantiate the clinically significant benefits of L-theanine augmentation.
L-theanine may increase focus. The combination of moderate levels of L-theanine and caffeine has been shown to significantly improve self-reported alertness and reduce self-reported tiredness. These results were part of a study performed in young adults (6).
L-theanine may help improve memory. A recent issue of Journal of Medicinal Food reports that the combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment. Neuropsychological tests and electroencephalography were conducted after 16 weeks of supplementation to evaluate the effect of treatment on memory and attention in 45 participants (7).
L-theanine may improve sleep quality. There is some early evidence that L-theanine could be beneficial for getting a good night’s sleep. Researchers of one study found that administration of 250 mg and 400 mg resulted in improved sleep quality in animal models and in human trials, including one study in individuals with schizophrenia.
In addition, 200 mg has been reported to promote a reduction in resting heart rate (8).
L-theanine has a lipid-lowering effect. The results of a rat study published in Bioscience, Biotechnology, and Biochemistry, showed that dietary powdered green tea had both anti-proliferative activity toward hepatoma cells and hypolipidemic (cholesterol lowering) activity (9).
L-theanine may boost the immune system. A number of recent studies suggest that L-theanine administration can improve the body’s immune system. The immune system plays a vital role in defending the body against viruses, bacteria and foreign bodies. Conventional methods of treatment for common illnesses usually involve a regimen of antibiotics, antivirals, immunosuppressant’s and dietary intervention that may support or enhance immune function.
One study highlighted the use of L-theanine as an intervention to decrease the incidence of upper respiratory tract infection symptoms. In elderly patients, supplementation with 280 mg and cysteine (700 mg) enhanced the primary antibody response to the influenza vaccine (10).
L-theanine may promote longevity. In a study of adult C. elegans roundworms, it appears that supplementation of 100-10,000nM can extend maximal lifespan by 4.4 percent (11).
While many more studies are needed, the results suggest that this compound may promote a healthy lifespan in mammals and possibly humans.
Although there are no reported side effects from taking L-theanine, consumption of large amounts of green tea can cause nausea, irritability and gastrointestinal upset due to the caffeine content.
Supplementation may interact with medications used to treat high blood pressure and stimulant medications (12).
More studies are needed to evaluate if and what side effects come with long-term use of supplements.
According to Psychology Today, 100 mg to 400 mg is recommended for sleep, stress and other uses; In combination with caffeine: 12-100 mg L-theanine and 30-100 mg caffeine is the recommended dose.
L-theanine is an amino acid found in tea leaves, predominantly green tea. It is known for its relaxing and stress-relieving effects. It is also being researched for its lipid-lowering, neuroprotective, anti-obesity and cancer fighting properties.
Studies show it may also be helpful when it comes to boosting the immune system and improving sleep quality, memory and focus.
As with many other supplements, most research on the basic actions of L-theanine has been done in animals. While some preliminary human studies have suggested benefits, much more research is needed.
There have not been reports of major adverse side effects with short-term use.