Pop quiz: why are the effects of tea different from those of coffee?
The answer: along with healthy antioxidants and reduced caffeine content, l-theanine is what sets true teas apart from other popular caffeinated beverages.
Scientists have studied this remarkable (and rare!) amino acid for its effects on focus, stress, brain health, immune function, and sleep.
In this article, you’ll learn how l-theanine works, what science says about the effects of l-theanine, and how to use it to support your health!
What Is L-Theanine?
L-theanine is a naturally-occurring amino acid, first discovered in green tea in 1949 by Japanese researchers (1).
You may know amino acids as the basic building blocks of life, but l-theanine is far from basic.
In fact, it’s only known to occur in two species: the tea plant (Camellia sinensis) and Bay Bolete mushrooms (Imleria badia or Xerocomus badius) (2). (While some websites state that the Moringa tree contains l-theanine, this claim is not based on scientific evidence, and appears to be untrue.)
Want to maximize your l-theanine infusion? Shade-grown teas (such as those used for matcha) may contain more l-theanine than other varieties (5). Additionally, researchers have observed that the quality and price of teas correlate closely to their l-theanine content (4).
Finally, l-theanine is also available in supplement form. You should be aware, however, that many supplement manufacturers use chemical synthesis or bacterial production to keep costs down – compared to extracting the amino acid from tea leaves (6).
How Does L-Theanine Work?
When you drink tea or take l-theanine orally as a supplement, it absorbs through your intestines, circulates in your bloodstream, and crosses your blood-brain barrier (7).
Researchers think that many of l-theanine’s effects occur due to its structural similarities to l-glutamine (a common amino acid) and glutamate (a neurotransmitter) (8).
While the evidence is preliminary, studies suggest that l-theanine may:
- Support higher brain levels of serotonin, dopamine, and GABA (8)
- Act as an antioxidant (9)
- Inhibit the “excitatory” neurotransmitter glutamate (8)
But what do these effects mean, practically speaking?
Keep reading to learn why you might want more l-theanine in your life!
5 Health Benefits of L-Theanine
1. Supports Calm Focus and Mental Clarity
Research suggests that l-theanine is the secret ingredient that causes caffeine from tea to behave differently from caffeine in coffee (10).
In other words, l-theanine has a direct impact on the effects of caffeine.
For example, one study found that because caffeine is arousing and l-theanine is calming, they partially counteract the effects of one another (11).
On the other hand, especially in high doses, caffeine and l-theanine may work together to increase cognitive performance better than caffeine alone (12).
And EEG studies show that alone or in combination with caffeine, 50-200 milligrams of l-theanine supports brain alpha wave activity (13)(14)(15). Alpha brain waves are associated with a state of calm focus or “alert relaxation” (14).
Another EEG study suggests that 25 milligrams of l-theanine per day supports theta wave activity, which may improve memory and cognition (16).
2. Supports a Healthy Stress Response
Numerous human studies suggest that consuming l-theanine regularly helps support a healthier response to stressful situations.
In one clinical trial, researchers concluded that l-theanine supported calm and helped the management of healthy blood pressure in adults who normally responded poorly to stress (17).
And in a separate study, 200 milligrams of l-theanine appeared to promote calm during and after multitasking, especially in anxiety-prone participants (18).
3. Supports Brain Health
Keep in mind that unlike most supplements, l-theanine crosses your blood-brain barrier.
And here’s what recent evidence suggests may happen when it reaches your brain:
- Neurogenesis (growth and repair of nerve cells) (21)
- Increased nitric oxide levels, resulting in neuroprotection and stabilized levels of neurotransmitters (22)
- Anti-neurotoxic effects (23)
- Reductions in the effects of glutamate, a neurotransmitter that is associated with anxiety and death of brain cells (8)(24)(25)
Along with supporting calm focus and a healthy stress response, l-theanine may also help support a healthy brain.
4. May Support Healthy Immune Function
According to a study from Brigham and Women’s Hospital, l-theanine may support a healthy immune response to infection (26).
And a separate study discovered that l-theanine may support your body’s natural anti-inflammatory response, which could be helpful for people with asthma (27).
5. May Support Better Sleep
In a randomized, double-blind trial, scientists found that people with anxiety slept better when they took high doses (450-900 milligrams) of l-theanine daily (28).
How to Take L-Theanine
Steeping tea longer and hotter may extract l-theanine more efficiently (32). And while small amounts of milk don’t affect l-theanine levels, adding a lot of milk may reduce the l-theanine content of your beverage (33).
Conversely, l-theanine supplements are convenient, but cost more than tea.
Also, keep in mind that without the combination of l-theanine and caffeine found in tea, supplements won’t have the same effects when it comes to focus. And they don’t offer all the other benefits of drinking tea, either.
Overall, l-theanine is extremely safe, with no serious reported adverse effects.
Based on the available evidence, the US FDA recommends a maximum daily l-theanine intake of 1200 milligrams (34).
However, if you’re getting your l-theanine from tea, make sure to pay attention to your tea intake. If you aren’t accustomed to it, drinking too much tea may result in an upset stomach, nausea, or jitters from excessive caffeine.
And if you’re currently taking medication, please consult your doctor for medical advice prior to adding l-theanine to your daily regimen.
Children, pregnant or breastfeeding women, and individuals with medical conditions should also speak to their doctor before trying l-theanine.
L-theanine is a gentle, effective way to support cognitive function, a healthier stress response, and better brain health. It’s also safer than most supplements, with no serious side effects.
Tea is the most cost-effective source of theanine, and also offers additional health benefits thanks to its catechins and polyphenol antioxidants.
However, supplements may be a better choice for people who prefer to limit their caffeine intake, or who wish to try higher doses of l-theanine.