L-theanine is an amino acid found naturally in green and black tea, that boosts mood, and promotes a sense of calm without drowsiness.
L-theanine Health Benefits
There have been a number of studies looking at the benefits of L-theanine. The FDA considers L-theanine as a GRAS (“Generally recognized as safe”) supplement.
L-theanine as a calming agent
In the world of brain chemistry, glutamate is an “excitatory” neurotransmitter. You can think of glutamate as the brain’s gas pedal.
By contrast, GABA is the calming agent in the brain.
For more on the neurotransmitter balance in our brains, see our Cognitive Health and Genetics Page.
Glutamate and GABA are both essential neurotransmitters, with important roles to play in cognitive function, however, when glutamate levels get too high, as they can during times of prolonged stress, the usually beneficial glutamate can become what is called an excitotoxin.1
In fact, chronically elevated glutamate has been linked to a number of neurological diseases. 2
This study found that L-theanine reduces physiological and psychological stress by blocking glutamate receptors in the brain. One of the primary reasons people experience an anti-anxiety effect when taking L-theanine is due to this glutamate blocking activity. Put simple, L-theanine helps take your foot off the brain’s gas pedal by acting as a glutamate antagonist.
L-theanine may improve sleep
In a randomized, double blind study, theanine was shown to significantly improve sleep quality in boys with ADHD. 3
L-Theanine can boost some markers of immune function
This 2008 study found that L-theanine helped to prevent contracting the cold and flu and had an immune boosting effect “enhancing gamma-delta T cell function.”
The New York Times, reporting on the study, had this to say in summary:
Tea increases the body’s defenses against infection and contains a substance (L-theanine) that may be turned into a drug to protect against disease, a study has found. Coffee does not have the same effect, the researchers say in an article today in Proceedings of the National Academy of Sciences. A component in tea primes the immune system to attack invading bacteria, viruses and fungi, the study concluded. An experiment showed that immune system blood cells of tea drinkers responded five times faster to germs than did the blood cells of coffee drinkers.
Theanine increases alpha brain waves
Alpha brain waves are the creative centers of the brain.
Studies show L-theanine improves alpha brain wave function, even at low 50 mg doses meant to mimic “normal dietary levels.”4
L-theanine and allergy
L-theanine has shown some promise as a modulator of allergic reactions. 5
A major event in allergic reactions is the secretion of histamine from immune cells known as mast cells. Mast cells can be thought of as the first responders of the immune system, they are constantly sensing the environment and when they detect something potentially harmful they secrete a wide range of factors to kick start the immune response. When mast cells detect something as harmful (even if it’s harmless) this causes an allergic reaction. 6 L-theanine inhibits histamine release from mast cells.
Interestingly, this inhibition of histamine also ties in with L-theanine’s glutamate inhibitory activities. Histamine can induce glutamate release, which as we’ve established above, is an excitatory neurotransmitter our bodies need. 7 Excess histamine may cause an unhealthy build-up of glutamate, although there is some evidence that there is an upper maximum of glutamate build-up associated with histamine.
L-theanine Side Effects
Low Blood Pressure and dizziness
L-theanine is contraindicated for those on high blood pressure medication because it lowers blood pressure further.8 Some people report episodes of light headedness after standing with repeated high doses of L-theanine.
There are many anecdotal reports of an overdose of theanine causing upset stomach in people experimenting with the supplement.
So the interesting questions then becomes how does L-theanine link all these together, and is there a single gene or SNP which is of particular interest?
Lets look at histamine first, a major gene involved in histamine metabolism is AOC1, which encodes for the enzyme Di-amine Oxidase (DAO – pay attention to that abbreviation as it’s the cause of much confusion). In health DAO functions to break down histamine following its release from mast cells, curtailing the immune response. There are several SNPs within AOC1 which are associated with reduced DAO activity, resulting in histamine intolerance, which is characterized by symptoms often associated with allergy such as headaches, flushing of the skin and irritation.
The benefit of L-theanine here is clear. By suppressing histamine release from mast cells, it is prevented from building up to harmful levels, even in those with reduced DAO activity. 9
We’ve already described how L-theanine can inhibit stress by blocking glutamate receptors. As excess histamine can lead to the buildup of glutamate there’s a clear mechanism for impaired DAO activity leading to increased histamine, leading to increased glutamate. L-theanine works by both preventing histamine release, and also blocking glutamate activity as well.
Most supplements contain doses of between 50 – 200 mg.
L-theanine is a potent nootropic that is widely regarded as safe. Many benefits have been shown from supplementing with theanine with stress reduction leading most people’s lists.
Do keep in mind that theanine can interact with some drugs and may lower blood pressure to a level that will be uncomfortable for some.
As theanine crosses the blood brain barrier, also be on the lookout for changes in mood after high doses.