Acute effects of theanine, caffeine and theanine–caffeine combination on attention

Abstract

Objective: l-theanine is a constituent of tea which is claimed to enhance cognitive functions. We aimed to determine whether theanine and theanine–caffeine combination have acute positive effects on cognitive and neurophysiological measures of attention, compared to caffeine (a positive control) and a placebo in healthy individuals.

Design: In a placebo-controlled, five-way crossover trial in 20 healthy male volunteers, we compared the effects of l-theanine (200 mg), caffeine (160 mg), their combination, black tea (one cup) and a placebo (distilled water) on cognitive (simple [SVRT] and recognition visual reaction time [RVRT]) and neurophysiological (event-related potentials [ERPs]) measures of attention. We also recorded visual (VEPs) and motor evoked potentials (MEPs) to examine any effects of treatments on peripheral visual and motor conduction, respectively.

Results: Mean RVRT was significantly improved by theanine (P = 0.019), caffeine (P = 0.043), and theanine–caffeine combination (P = 0.001), but not by tea (P = 0.429) or placebo (P = 0.822). VEP or MEP latencies or SVRT did not show significant inter-treatment differences. Theanine (P = 0.001) and caffeine (P = 0.001) elicited significantly larger mean peak-to-peak N2-P300 ERP amplitudes than the placebo, whereas theanine–caffeine combination elicited a significantly larger mean N2-P300 amplitude than placebo (P < 0.001), theanine (P = 0.029) or caffeine (P = 0.005). No significant theanine × caffeine interaction was observed for RVRT or N2-P300 amplitude.

Discussion: A dose of theanine equivalent of eight cups of back tea improves cognitive and neurophysiological measures of selective attention, to a degree that is comparable with that of caffeine. Theanine and caffeine seem to have additive effects on attention in high doses.

Keywords:

• Theanine
• Caffeine
• Tea
• Cognitive effects
• Attention
• Reaction time
• P300
• Event-related potentials

Disclaimer statements

Contributors CNK, TLD, AMTA and VSW designed the research; CNK conducted the research; VSW and AMTA provided essential material and equipment, CNK and TLD analyzed data and wrote the paper; CNK, TLD, VSW and AMTA revised and edited the manuscript; CNK had the primary responsibility for final content.

Funding This study was funded by the National Research Council Grant 09-32 and the International Research Centre of University of Peradeniya, Sri Lanka.

Conflict of interest The authors have no potential conflict of interest.

Ethics approval The study was approved by the Research Ethics Committee of the Faculty of Medicine, University of Peradeniya, Sri Lanka.

ORCID

Tharaka L. Dassanayake http://orcid.org/0000-0002-7963-9012