L-Theanine is present almost exclusively in the tea plant, Camellia sinensis. Other species have been found to produce minor amounts of L-theanine including one mushroom1 and twenty-four other Camellia species.1,3
L-Theanine comprises approximately 1 to 2% of the dry weight of tea leaves.
L-Theanine contributes to the taste of tea, eliciting the umami flavor (a Japanese word which roughly translates to "tasty") and a sweet taste.2,6
L-Theanine was discovered in 1949 and has been used as a food additive in Japan since 1964.1
Sunlight converts L-theanine to polyphenols; certain teas are grown out of direct sunlight to prevent this conversion and protect the flavor of the tea.
L-Theanine is a uniquely modified amino acid. It is formed from the ethylation of glutamine.
Gamma-glutamylethylamide and 5-N-ethyl-L-glutamine are synonyms for L-theanine.
Proteins do not contain L-theanine; it is only found as the free amino acid.
L-Theanine crosses the blood-brain barrier through the neutral amino acid transport system. 1
L-Theanine is generally well tolerated and has been approved as a safe food additive in the United States and Japan. Although not determined for humans, the LD50 for rats is greater than 5000 mg/kg. L-Theanine in not mutagenic or carcinogenic in animals or bacteria.
Most supplements do not contain pure L-theanine. Instead, most supplements were found to contain a 50:50 mixture of D-theanine and L-theanine. The safety of D-theanine or the mixture of D and L isomers has not been determined.11
The activity of chemotherapeutic drugs is increased by L-theanine. Specifically, the activities of doxorubicin, idarubicin, pirarubicin, and irinotecan are increased in tumor cells. Caution during chemotherapy is warranted until this relationship is well-characterized.
Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
Source density analysis of the human EEG after ingestion of a drink containing decaffeinated extract of green tea enriched with L-theanine and theogallin.
A small randomized, placebo-controlled study investigated a decaffeinated green tea drink on EEG. Twelve healthy people participated in the study. EEG and visually evoked P300 potentials were recorded hourly for four hours after consuming the supplement or placebo. After consuming the supplement, a general attenuation of electrical delta power (eyes open) was observed during the first hour (p<0.01). Increases of delta and theta power were observed beginning in the second hour at frontal electrode sites during a reading test; this result was significant at the third and fourth hour (p<0.04) versus placebo. Visually evoked P300 waves showed a decrease in latency at hour four (p<0.04). The results of this small clinical trial indicate that theanine and theogallin have a stimulatory effect, even without caffeine.10
The combined effects of L-theanine and caffeine on cognitive performance and mood.
A small trial investigated the effect of caffeine (50 mg), caffeine and L-theanine (50 mg and 100 mg, respectively), or a placebo on cognitive functioning in twenty-seven healthy volunteers. Word recognition, rapid visual information processing, critical flicker fusion threshold, attention switching, and mood were assessed at baseline, 60 minutes after consuming one of the three treatments, or 90 minutes after consuming one of the treatments. The assessments were separated by a seven day washout period. Caffeine alone was found to improve subjective alertness after 60 minutes and accuracy on the attention switching test after 90 minutes. Caffeine plus L-theanine was found to increase both speed and accuracy on the attention switching test after 90 minutes. Caffeine with L-theanine also decreased susceptibility to distraction on memory tasks at both 60 and 90 minutes post supplement. This small study indicates that caffeine with L-theanine beneficially affects cognitive performance.7
The effects of L-theanine on alpha-band oscillatory brain activity during a visuo-spatial attention task.
Alpha-band oscillatory brain activity was assessed during a visuo-spatial attention task in thirteen normal volunteers. Participants consumed 250 mg theanine in water or a water placebo prior to accomplishing the attention task. Each subject performed the task twice, on separate days, once with the theanine and once with the placebo. L-Theanine supplementation produced a significant reduction in tonic alpha compared to placebo. This change was accompanied by a shift in scalp topography indicative of indicative of treatment-related changes in the neural generators of oscillatory alpha activity. No changes in cue-related anticipatory alpha effects were identified. This study indicates that theanine may impact attention sustainment. Further studies are needed to evaluate these results and to define specific functions of L-theanine.8
L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance.
A placebo-controlled trial investigated the affect of L-theanine and caffeine on cognition in sixteen paid volunteers. Participants performed an attention for four sequential days, once each with placebo, 100 mg L-theanine, 50 mg caffeine, or both theanine and caffeine. The task involved cued shifts of attention to the left or right visual hemifield in anticipation of an imperative stimulus requiring discrimination. Overall, tonic attentional focus as well as phasic, cue-dependent anticipatory attentional biasing, as indexed by scalp-recorded alpha-band (8–14 Hz) activity were assessed. The combined treatment significantly improved behavioral performance in terms of hit rate (P<0.016) and target discriminability (P<0.002). Caffeine along significantly improved target discriminability compared with placebo (P<0.016). L-Theanine alone did not significantly impact any measure. Reaction time was not altered by any treatment. Electrophysiological results showed lower overall tonic alpha power in the combined treatment. These results suggest that L-theanine with caffeine may have beneficial effects for attention.9
Effects of oral supplementation with cystine and theanine on the immune function of athletes in endurance exercise: randomized, double-blind, placebo-controlled trial.
A randomized, double-blind, placebo-controlled trial investigated the efficacy of a cystine plus theanine supplement on immune function in athletes during endurance training. Fifteen male long distance runners participated in the study. Participants consumed a supplement containing 700 mg cystine and 280 mg theanine or a placebo daily for ten days prior to beginning an endurance training camp. Blood samples were collected on the first and last days of a two-week endurance training program. At the end of the training program, significant decreases in neutrophil and high-sensitivity C-reactive protein were noted in the placebo group (P=0.018 and P=0.047, respectively) but not in the supplemented group (P=0.460 and P=0.688, respectively). There was also a trend for a decrease in lymphocytes in the placebo group only (P=0.087), although this did not reach statistical significance. This small preliminary study suggests that theanine and cystine may help to protect immune function in athletes. Further studies are necessary to explore this result and to evaluate whether this protection extends to people who are not endurance athletes.4
Co-administration of l-cystine and l-theanine enhances efficacy of influenza vaccination in elderly persons: nutritional status-dependent immunogenicity.
A randomized, placebo controlled trial investigated the impact of two weeks of L-cystine and L-theanine on immune response to influenza vaccine in elderly people. Sixty-five elderly people living in a nursing home were randomly assigned to receive a combined supplement containing L-cystine and L-theanine or a placebo. Supplements were consumed daily for fourteen days prior to vaccination. Serum antibody titers were assessed prior to and four weeks after vaccination. Vaccination significantly increased hemagglutination inhibition (HI) titers for all the three strains of influenza viruses (A/New Caledonia [H1N1], A/New York [H3N2] and B/Shanghai) in both groups. There was no difference in HI titers between the supplemented and placebo groups. The rate of seroconversion for influenza virus A (H1N1) was significantly higher for people with low serum total protein (63% vs. 10%, P<0.05) of low hemoglobin (71% vs. 9%, P<0.05). This study indicates that a combination of L-cystine and L-theanine improve response to influenza vaccination for elderly people with low serum total protein or low hemoglobin.5
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