Calm

L-theanine relaxed healthy adults

Stress-hormone cortisol levels decreased

Humans use the stress response to survive threats, and to help achieve challenging goals, but chronic stress can have negative health effects. In this study, 15 healthy adults reporting moderate levels of stress took a placebo or a single 200 mg dose of L-theanine, pausing for a week, then switching supplement and placebo groups.

To induce stress, doctors gave a mental math test before, and 45 minutes after, the supplement. Blood pressure and heart rate increased during the math test, with participants reporting greater levels of stress and anxiety. Three hours after taking L-theanine, alpha power brain wave activity—typical of relaxation, meditation, and deep sleep—increased in the frontal region of the brain. Researchers also saw salivary cortisol levels decrease following the math test in the L-theanine group, suggesting reduced stress.

Doctors pointed out the study took place during the Covid-19 pandemic, which negatively affected worldwide population physical and mental health.

Reference: Neurology and Therapy, 2021, Vol. 10, 1061-78