L-theanine Found to Help Reduce Stress and Improve Cognitive Function
L-theanine is an amino acid that is found in green and black teas. A new study suggests that it may help reduce stress and improve cognitive function.
Thirty adults with an average age of 48 and no major psychiatric illness participated in the study. The participants took 200 mg/day of L-theanine or a placebo for four weeks. They switched interventions after a 2-week washout period.
The researchers assessed depression, anxiety, and sleep quality via the Self-rating Depression Scale, the State-Trait Anxiety Inventory, and the Pittsburgh Sleep Quality Index. Cognitive function was assessed using the Trail-Making Test and the Stroop test. The assessments took place at baseline, 4 weeks, 6 weeks, and 10 weeks.
Participants had improvements in Pittsburgh Sleep Quality Index scores for sleep latency and daytime dysfunction while taking the L-theanine, compared to while taking the placebo. They also used less sleep medication. Anxiety and self-reported depression decreased while taking the L-theanine.
Verbal fluency and executive functions scores improved after taking L-theanine for 4 weeks. They biggest improvements were seen in participants who had poorer baseline cognitive function.
The study was conducted by researchers from the National Center of Neurology and Psychiatry, Tokyo. It was published on October 3, 2019 in the journal Nutrients.