L-theanine: what it is, benefits and health risks

L-theanine (L-theanine) is a naturally occurring compound in green and black tea, also found in dietary supplement form, that has a number of health benefits, such as improved powers of concentration.


L-theanine is an amino acid that is not produced by the human body and is not essential for humans. Green tea, black tea and certain types of mushrooms naturally contain L-theanine. This substance may have an effect on levels of certain chemicals in the brain, including serotonin and dopamine (which influence mood, sleep and emotions) and cortisol, which helps the body cope with stress. A change in the balance of these chemicals can change a person's mood or stress level.


Various small studies and animal tests have shown that L-theanine can provide a number of benefits. Experts believe it is generally a safe compound for health, but extensive, high-quality human research confirming the benefits of L-theanine is currently lacking. What are the purported benefits of L-theanine?

 

Better mental concentration

Many people drink black or green tea while working because they have noticed it increases their mental focus. A 2012 study¹ supports this idea. Researchers found that people who took 100 mg of L-theanine made fewer errors in an attention-demanding task than those in the placebo group. Taking 50 mg of caffeine or combining L-theanine and caffeine also improved participants' concentration. More research is needed, however, to find out how L-theanine might influence a person's attention and concentration.

 

Improved sleep

L-theanine may help people who want to fall asleep more easily. Several studies have suggested that L-theanine might help people relax before bed, fall asleep faster and sleep more soundly. These benefits may result from the specific effects the amino acid has on chemicals in the brain that play a role in sleep.


A 2018 study found that participants reported greater sleep satisfaction after taking 450-900 mg of L-theanine daily for 8 weeks. Participants in that study suffered from generalized anxiety disorder and were on antidepressants. The study authors noted that no improvements in anxiety were reported.

 

Relaxation

Many people often drink a cup of tea or other hot drink 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.

 

Increased cognitive performance

In 2016, a scientific team reviewed existing research on the benefits of L-theanine² and concluded that this compound could benefit a person's mental and physical health. Scientists noted that L-theanine appears to have neuroprotective effects that improve brain function.

By itself, L-theanine may improve a person's attention and reaction time. In combination with caffeine, it may lead to improved alertness and a knack for working with numbers. Caffeine is a stimulant, so it can help people stay alert and focused.

However, not all research has shown that L-theanine can improve people's cognitive abilities. Scientists believe more complex studies are needed to clarify the effects of this compound on mental function.