L-theanine, scientifically known as gamma-glutamylethylamide, is an amino acid.But it’s an unusual amino acid because it isn’t present significantly in the human diet. Nor is it used to make proteins in the body. So, it’s not an essential nutrient but that doesn’t undermine its usefulness in many aspects of human health and performance.

Indeed, the last few years have seen a plethora of research studies on the effects of L-theanine in animals and humans. Evidence is accumulating for its ability to not only enhance relaxation and improve concentration and learning ability; but also, to bring longer term health benefits by supporting cardiovascular health, immune function, appetite control and an overall sense of wellbeing as you’ll see here.

Sources of L-theanine

Drinking tea (black, white or green) may provide some L-theanine. Levels present tend to vary across studies but a 2011 analysis at Bristol University found approximately 24mg theanine in a standard cup of black tea, compared to only 8mg in a cup of green tea (Keenan et al 2011). These levels are lower than the 200mg typically found to benefit human health in trials. You’d need to drink eight cups of black tea, or many more cups of green tea, to get the same dose of L-theanine used in the trials!

What’s more, the addition of milk tends to reduce the L-theanine content of tea in a dose-linear fashion; while other constituents of tea, especially the amino acid L-glutamine, may hamper the absorption of L-theanine.

Mechanisms of Action in Human Cells

L-theanine has been shown to act directly on brain chemistry, as it can cross the blood brain barrier, reaching the brain within an hour of consuming it.

Once within the brain, L-Theanine increases brain waves called alpha-1 waves. These are known to promote a sense of relaxation without drowsiness – indeed they also improve mental alertness and attention. Taking a therapeutic dose of L-Theanine (100 to 200mg), has been shown to induce such effects in humans often within 30 to 45 minutes of ingestion. Effects seem to be particularly marked in people who are more prone to anxiety or stress.

Studies have shown L-Theanine to affect various different neurotransmitters. It seems to inhibit the function of the ‘fight or flight’ chemical noradrenaline and the excitatory chemical glutamate, both of which can be toxic at high levels. Conversely, L-theanine may enhance dopamine and gamma-butyric acid – GABA. GABA is known for keeping neurochemistry in balance, resulting in an overall calming effect, while dopamine promotes motivation and focus.

This combination of its ability to cross the blood brain barrier, to affect alpha waves and to modulate all these neurotransmitters, makes L-theanine uniquely placed to enhance relaxation without causing drowsiness. Thus, it stands apart from many other stress-reducing supplements and may be more widely applicable to the challenges of daily life.

Typical Clinical Uses

Stress and Anxiety

L-theanine has been well studied for its effects on stress and anxiety. A systematic review and meta-analysis earlier this year evaluated nine randomized controlled trials (RCTs) and concluded a reduction in stress and anxiety in people exposed to stressful conditions. For example, a trial of 30 healthy individuals found that 200mg L theanine/day for 4 weeks resulted in reduced levels of stress, low mood and anxiety. Cognitive attention and focus is also typically improved with L-theanine in individuals who have high baseline anxiety levels.

Another review included individuals with medically diagnosed anxiety disorders, looking at trials lasting up to eight weeks, and concluded that doses of 200 to 400mg/day are safe and induce anxiolytic and anti-stress effects in both acute and chronic conditions.

The stress and anxiety-reducing effects of L-theanine have also been shown to attenuate stress-related rises in blood pressure in humans.

In practice: 200 to 400mg/day may help attenuate rising levels of anxiety and related symptoms triggered by potentially stressful situations.

Sleep

Taking L-theanine before bed may help you to fall asleep more quickly and easily and to improve the quality of sleep. But L-theanine doesn’t typically act as a sedative. Rather, the mechanism by which it can promote a good night’s sleep is through its ability, as we’ve seen above, to reduce anxiety and promote relaxation. RCTs report improvements in both the quality and the quantity of sleep; and people who experience such a benefit tend to describe L-theanine as an agent that helps to turn off unwanted background noise and rumination.

In practice: Taking 200mg to 400mg L-theanine before bed may help some people to sleep better, especially people with higher baseline levels of stress and proneness to rumination.

Cognitive Function and Memory

Evidence from human trials indicates an important role for L theanine in improving cognitive function. A recent RCT of thirty healthy individuals reported executive function and verbal fluency scores improved with L-theanine (200mg/day for four weeks), and especially letter fluency in the individuals with lower pre-trial scores.

Other studies have found that L-theanine can improve concentration and that this effect is further enhanced when combined with caffeine. A randomized four-way crossover study of nine healthy men, for example, reported that combining L-theanine (200mg) with caffeine (160mg) led to significantly reduced mind-wandering during visual discrimination tasks, enhancing attention to the task at hand, compared to L-theanine alone, which itself had a greater effect than placebo.

In practice: 180 to 200mg L-theanine/day for some weeks may improve aspects of cognition, memory and concentration in healthy people and (for memory) in those with mild cognitive impairment. Concentration may be further enhanced when L-theanine is combined with caffeine.

Cardiovascular Health

Tea consumption has long been associated with beneficial cardiovascular effects, possibly because of its antioxidant phenols but also perhaps because of its L-theanine content: As well as helping to prevent stress-induced rises in blood pressure, (outlined above), L-theanine may enhance blood flow by promoting the synthesis of endothelial nitric oxide (eNO). eNO acts as a relaxant within the vascular endothelium, promoting vasodilation and improving circulation.

In practice: there is far less evidence for L-theanine’s benefit on cardiovascular health than on cognitive and psychological health. But preliminary evidence indicates that 50 to 200mg/day may support healthy blood flow.

Immune Function

L-theanine has been shown to have significant immune supportive effects. Data from animal studies indicates this effect arising from L-theanine’s ability to increase splenic weight, alter the balance of immune chemicals (such as Th2/Th1 cytokines), reduce circulating corticosterone and elevate dopamine and serotonin levels in the brain. L-theanine was also found to alleviate immune stress (measured by secretory IgA, cortisol, glycoproteins and inflammatory cytokines) in chickens challenged with toxic lipopolysaccharides.

A double blind study of 20 elite athletes reported L-theanine (150mg/day for 6 weeks) to improve post-exercise immune function by beneficially altering disruptions in the balance of T-helper cell subtypes (specifically Th1/Th2).

In practice: As intense sports training can suppress immune function, individuals who train hard may benefit from taking a daily dose of 150 to 200mg L-theanine.

Dosage

Most studies use between 100 to 400mg a day, with a maximum of 200mg at a single dose. To optimize uptake from the intestine and across the blood brain barrier, L-theanine may be best taken on an empty stomach, and especially away from protein foods and amino acid-containing supplements.