The Benefits of L-Theanine

Green tea pour and assorted loose teas
Clive Champion - Champion Photography Ltd./Taxi/Getty Images

There's something calming about sipping a cup of green tea, and it may be the L-theanine. An amino acid found naturally in green tea, L-theanine is said to alleviate anxiety, improve sleep, and reduce stress.

Uses for L-Theanine

Proponents claim that L-theanine can help with a variety of health concerns, such as anxiety, depression, high blood pressure, high cholesterol, insomnia, and stress.

L-theanine is also purported to increase concentration, promote weight loss, and boost the immune system. In addition, some proponents suggest that L-theanine can prevent stroke, Alzheimer's disease, and some forms of cancer.

The Benefits of L-Theanine

To date, scientists have yet to extensively explore the benefits of L-theanine. However, preliminary research suggests it may help lift mood, enhance brain function, and calm the body's response to stress and anxiety. Here's a look at some key study findings:

1) Anxiety

L-theanine may help to reduce anxiety, according to a 2016 study. Healthy participants consumed a drink containing 200 mg L-theanine or a placebo. One hour after consumption, the stress response to a cognitive stressor was significantly reduced in those who consumed the L-theanine drink. Three hours after consumption, saliva cortisol (a hormone secreted in response to stress) was significantly lower.

Another study explored the effects of regular consumption of L-theanine and found that daily intake decreased subjective stress and saliva levels of α-amylase (an enzyme released in response to stress) in undergraduate students undergoing stress.

2) Sleep

A preliminary study examined the effects of a low-caffeine green tea on sleep quality (caffeine in green tea can interfere with sleep and may counteract the effect of theanine). After consuming a low-caffeine green tea daily for seven days, saliva alpha-amylase levels were significantly lower in those who drank the low-caffeine green tea than in those who consumed the standard green tea. Sleep quality was higher in those who had consumed a larger amount of low-caffeine green tea.

3) Depression

A 2017 study published in Acta Neuropsychiatrica explored the use of L-theanine for major depression. The trial included 20 men and women who had 250 mg of L-theanine added to their current medication for eight weeks. They found it had multiple benefits in relieving anxiety, sleep disturbances, and cognitive impairment associated with depression.

4) Cognitive Function

A 2010 study from Nutritional Neuroscience suggests that a combination of L-theanine and caffeine may help improve cognitive performance.

For the study, 44 young adults took either a placebo or a combination of L-theanine and caffeine prior to performing a demanding cognitive task. Researchers found that the combination of L-theanine and caffeine significantly improved accuracy and alertness. It also helped to increase focus while performing the task.

5) Weight Loss

L-theanine shows promise as a weight loss aid, according to preliminary animal-based research published in the journal In Vivo. In an experiment involving mice fed green tea powder, researchers found that L-theanine and caffeine found in the powder appeared to prevent weight gain and fight the buildup of fat.

Side Effects

To date, little is known about the safety of using L-theanine supplements in the long term. L-theanine is generally considered safe when consumed in green tea, however, the National Institutes of Health cautions against drinking more than five cups of green tea daily.

Due to the caffeine content, excessive consumption of green tea may also trigger certain side effects. These may include a headache, insomnia, irritability, diarrhea, and heartburn.

There's also some concern that taking L- theanine in combination with sedatives, lipid-lowering medications, and/or drugs used in chemotherapy may produce harmful effects.

Dietary supplements have not been tested for safety. Because they are largely unregulated, the content of some products may differ from what is specified on the product label.

Also, keep in mind that the safety of supplements in pregnant women, nursing mothers, children, and those with medical conditions or who are taking medications has not been established.

Where to Find L-Theanine

Widely available for purchase online, L-theanine supplements are sold in many natural-food stores and in stores specializing in dietary supplements.

L-theanine is also found in green tea. Although the content varies, a cup of tea contains around 25 mg of L-theanine.

The Bottom Line

While increasing your L-theanine intake by consuming green tea on a regular basis may help enhance your overall health, it's too soon to recommend L-theanine supplements for any health condition. 

If you're considering the use of L-theanine supplements, talk with your doctor first. Self-treating a condition and avoiding or delaying standard care may have serious consequences.

Disclaimer: The information contained on this site is intended for educational purposes only and is not a substitute for advice, diagnosis or treatment by a licensed physician. It is not meant to cover all possible precautions, drug interactions, circumstances or adverse effects. You should seek prompt medical care for any health issues and consult your doctor before using alternative medicine or making a change to your regimen.