Learning About L-Theanine Benefits – Sharon Palmer, The Plant Powered Dietitian

L-theanine in tea and supplements may have benefits for anxiety, brain health, and sleep. Learn more about l-theanine benefits in this expert review.

If you’re like the millions of people who are looking for natural relief for issues like anxiety, stress, insomnia, and brain health, you might have heard about a supplement or compound found in tea called l-theanine. What is l-theanine? L-theanine is a water-soluble, nonprotein amino acid that is naturally found in green and black tea leaves, as well as certain varieties of mushrooms. The leaves of the Camellia sinensis plant are used to make green, black, and oolong tea, and contain moderate amounts of l-theanine. The amount of l-theanine present in tea depends on several variables, including the variety of tea, the geographic region it was grown in, and when and how it was harvested. However, a cup of green tea typically contains 8-30 mg of l-theanine, while supplement forms of the amino acid are usually sold in 200 mg or 400 mg doses.  L-theanine is not made by the human body, nor is it an essential nutrient that must be obtained from the diet, but that’s not to say it shouldn’t be included in the diet. Despite l-theanine not being classified as an essential nutrient, researchers are studying how its supplemental use may provide a range of health benefits, in particular for helping anxiety, stress, insomnia, and cognition.

L-theanine supplements are available, including as an ingredient in many wellness blends. 

Further research is required to fully understand the full range of effects that l-theanine supplements have on human health. However, it is believed to be associated with an increase in neurotransmitters, alpha brain wave activity, and cell protection from damage by free radicals. Study subjects have been reported to have increased levels of serotonin, dopamine, and gamma-aminobutyric (GABA) in the brain after taking l-theanine, which suggests that l-theanine may increase neurotransmitters. People have also reported feeling more relaxed, calm, and focused after taking l-theanine supplements, which researchers believe could be attributed to an increase in alpha brain wave activity. Additionally, l-theanine is known to contain antioxidant properties, which may help protect cells from damage against free radicals in the body. Although research is ongoing, studies have shown that this supplement can provide a range of benefits, including improved cognitive function, an improved immune system, lowered blood pressure, lowered stress, enhanced mood, and better sleep.

L-theanine is a naturally found ingredient in green and black tea

Four L-Theanine Benefits

Research has found the following potential health benefits for l-theanine consumption. 

1. Improves Cognitive Function

A study in which people were given a 100 mg supplement of l-theanine or a placebo showed that the people who were given the l-theanine made fewer errors in their attention task than the control group. Associations have also been made between taking l-theanine with caffeine and an even greater increase in concentration and focus.

2. Lowers Stress and Blood Pressure

Researchers have found that moderate doses of l-theanine can lower the resting heart rate and help lower spikes in blood pressure in response to stressful situations where people’s blood pressure previously spiked. In one study, a 200 mg dose of l-theanine lowered the resting heart rate of participants, which can help reduce stress and promote relaxation.

3. Improves Relaxation and Sleep

Many people drink green or black tea in the evenings to relax and prepare themselves for a good night’s rest. One of the reasons for tea’s relaxing properties is likely l-theanine.  Consuming l-theanine has been shown to slow the resting heart rate, aid in relaxation, and promote more deep and restful sleep. Researchers from one study observed that doses of 250-400 mg of l-theanine improved sleep in animals and humans.

4. Improves the Immune System

Several studies have demonstrated how l-theanine can benefit the immune system.  Although more research is needed, studies have linked the supplementation of l-theanine to a decrease in upper respiratory infections, improved intestinal tract inflammation, and, when coupled with the antioxidant properties of green tea, to successful flu prevention.

A variety of green and black teas contain l-theanine

Who Should Take L-theanine?

What is the l-theanine dose for anxiety and other benefits? The recommended dose typically ranges from 200-400 mg per day, but this varies depending on the product and the individual, and additional research is needed to determine proper doses. These supplements are available in capsule, tablet, soft gel, and powder form; you can purchase supplements from health food stores, pharmacies, and online retailers. As with any supplement, choosing a credible brand and following the instructions is essential. I always recommend third-party tested supplements. The most common seals to look for are NSF-certified, BSCG-certified, and USP-verified. Although L-theanine is generally safe, it could react with certain medications and is not fit for everyone. Therefore, it is also crucial to talk to your doctor before taking l-theanine supplements, especially if you are pregnant, receiving chemotherapy treatments, or taking blood pressure medications. One safe way to enjoy the anti-anxiety benefits of l-theanine is through curling up to a cup of green or black tea more often, as is the tradition in many healthful diet patterns, such as the Japanese diet. 

For more blogs on health and wellness, check out some of my latest: 

Written by Anna Tobin, dietetic intern with Sharon Palmer, MSFS, RDN


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Fontaine, D., & Mehta, F. (2021, January 20). L-Theanine: Dosage, Benefits, and Side Effects. Healthline. Retrieved August 24, 2023, from https://www.healthline.com/health/l-theanine

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