L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study

ABSTRACT

Objective: L-theanine, a non-proteinic amino acid found in tea, is known to enhance attention particularly in high doses, with no reported adverse effects. We aimed to determine whether oral administration of L-theanine acutely enhances neurophysiological measures of selective attention in a dose-dependent manner.

Methods: In a double-blind, placebo-controlled, counterbalanced, 4-way crossover study in a group of 27 healthy young adults, we compared the effects of 3 doses of L-theanine (100, 200 and 400 mg) with a placebo (distilled water) on latencies of amplitudes of attentive and pre-attentive cognitive event-related potentials (ERPs) recorded in an auditory stimulus discrimination task, before and 50 min after dosing.

Results: Compared to the placebo, 400 mg of theanine showed a significant reduction in the latency of the parietal P3b ERP component (p < 0.05), whereas no significant changes were observed with lower doses. A subsequent exploratory regression showed that each 100-mg increase in dose reduces the P3b latency by 4 ms (p < 0.05). No dose–response effect was observed in P3b amplitude, pre-attentive ERP components or reaction time.

Discussion: The findings indicate L-theanine can increase attentional processing of auditory information in a dose-dependent manner. The linear dose–response attentional effects we observed warrant further studies with higher doses of L-theanine.

KEYWORDS:

• theanine
• attention
• cognition
• event-related potentials
• P300
• reaction time
• dose-response effect
• placebo-controlled trial

Acknowledgements

This work was supported by University of Peradeniya under Grant URG/2016/45/M. We thank Dr Menaka Dharmawardena and Ms L. Shiroma for their assistance in data collection, and Dr Ross Fulham for his contribution in writing EEG data processing scripts. We also thank Dr Tissa Amarakoon for his comments on the project proposal.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by University of Peradeniya [grant number URG/2016/45/M].

Notes on contributors

Tharaka L. Dassanayake

Tharaka L. Dassanayake is the Professor in Neurophysiology at the Faculty of Medicine, University of Peradeniya.

Chanaka N. Kahathuduwa

Chanaka N. Kahathuduwa is an Assistant Professor at the Department of Laboratory Science and Primary Care, Texas Tech University Health Sciences Center.

Vajira S. Weerasinghe

Vajira S. Weerasinghe is the Professor of Physiology, Faculty of Medicine, University of Peradeniya. All authors conceptualized and designed the study. TLD collected the data. TLD and CNK analysed the data. TLD prepared the first draft of the manuscript and CNK and VSW contributed to revise the draft versions of the manuscript. All auhors read and approved the final submission.