Several clinical trials have examined the effects of L-theanine, alone or in combination with caffeine or green tea, on brain health. No human studies have tested it for the prevention of dementia or cognitive decline.
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Our search identified:
• 1 meta-analysis based on 10 randomized controlled trials testing acute effects of L-theanine alone or in combination with caffeine in healthy adults
• 6 randomized controlled trials (3 testing acute effects, 2 examining brain activity, and 1 with green tea extract in people with mild cognitive impairment)
• 1 open-label study in people with major depressive disorder
• 1 review
• Numerous preclinical studies
The long-term effects of L-theanine on cognitive health are unknown, but a few short-term human studies have shown small benefits. In a randomized controlled trial in patients with mild cognitive impairment, L-theanine taken with green tea extract for 16 weeks had no significant effect on memory and attention, though a trend for an improvement in memory was seen midway through the trial [1]. The patients who had more severe impairment at the start of the trial appeared more likely to benefit from treatment, but these results have not yet been replicated.
Combinations of L-theanine and caffeine have been reported to acutely improve attention and alertness in small clinical trials, but the positive effects have been primarily attributed to caffeine [2]. L-theanine may interact with caffeine, improving attention and ability to ignore distractions, and together, enhance performance on cognitively demanding tasks [3]. In a small randomized controlled trial of healthy adults, L-theanine alone did not affect attentional focus [4]. Other studies have reported mixed effects, with L-theanine decreasing the beneficial effects of caffeine on cognition and mood [5].
Preclinical studies have reported that L-theanine may reduce brain cell death [6] and oxidative damage [7], and increase levels of protective chemicals [8], but these effects have not been confirmed in humans.
It is currently unknown whether L-theanine can improve cognition or slow cognitive decline in people with dementia. While some benefits have been observed in preclinical studies of Alzheimer's disease [6], L-theanine has not been clinically studied in dementia patients.
Large meta-analyses of long-term tea consumption (containing L-theanine) have found that side effects are mild [9][10] but these results on tea may not apply to supplements. In a short randomized controlled trial, an L-theanine supplement (400 mg/day) was well-tolerated with no significant adverse events [11]. Larger, long-term studies are needed. For more information on green tea, please review our separate report.
The interactions between L-theanine and other drugs have not been well-studied. Clinical data suggest that L-theanine lessens the blood pressure increase caused by caffeine [12][13]. Because of its possible effects on blood pressure [12][14], it may be dangerous to use in combination with blood pressure medications.
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
The following sections discuss the existing evidence for the possible benefits of L-theanine.
Many people drink black or green tea while at work, believing that it boosts their mental focus. A study focusing on the effects of L-theanine on cognitive function in older adults appears to support this.
Researchers in this study looked into whether the regular intake of theanine in the form of green tea for 12 weeks could improve subjects’ attention and cognition.
They concluded the study with positive initial findings, stating that attentional function and working memory did appear to improve with L-theanine consumption.
However, they also stated that more research is necessary to determine how L-theanine might affect a person’s attention and focus.
There is a need for more high-quality research to clarify the effects of this compound on people’s mental functions.
Several studies have suggested that L-theanine could help people relax before bedtime, get to sleep more easily, and sleep more deeply.
Contact us to discuss your requirements of L-Theanine for Cognitive. Our experienced sales team can help you identify the options that best suit your needs.
These benefits may result from the specific effects that the amino acid has on brain chemicals that play a role in sleep.
A study found that people reported having greater sleep satisfaction after taking 450–900 mg of L-theanine daily for 8 weeks. The study participants had generalized anxiety disorder and were taking antidepressants.
The authors noted that there were no reported improvements in anxiety or insomnia severity.
People often drink a cup of tea or another hot beverage to help them relax. Research suggests that the L-theanine in green or black tea may contribute to this feeling of relaxation by reducing a person’s resting heart rate.
As part of a calorie-controlled diet, replacing a snack with green tea or another low-calorie hot beverage could aid weight loss.
The L-theanine in green tea can create a savory taste, also known as umami flavor. Research suggests that umami flavors may increase feelings of fullness, which often helps with weight loss.
L-theanine may support the body in fighting off illness. Several studies have suggested that taking L-theanine could boost a person’s immune system, making them less likely to get common colds or the flu.
Its potential anti-inflammatory effects could also help fight illness.
Research has linked high blood pressure with a higher risk of several health problems, including heart attack and stroke.
L-theanine may help reduce stress, and a reduction in stress and increased relaxation can lower the heart rate. In turn, this may help lower blood pressure.
Some research on animals suggests that L-theanine may help to increase kidney function and protect the kidneys from damage during the use of a chemotherapy drug called doxorubicin.
However, scientists need to do more research to understand the specific interactions between these chemicals.
While there is some evidence that L-theanine could benefit people’s mental and physical health, more studies are necessary before doctors can be sure of the actual effects of this compound. Scientists have not yet conducted high-quality research in humans.
Many studies to date have had a small sample size, meaning that very few people took part in the research. Data from just a small number of people are less likely to be conclusive than those from larger groups.
Other studies have used animals, such as rats or mice. However, humans are likely to react differently to animals, so these results may not be applicable.
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