High-dose L-theanine-caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acutely sleep-deprived young adults: a double-blind, placebo-controlled crossover study.
- 2025-08-12
- The British journal of nutrition 134(3)
- Gayani S Nawarathna
- Dewasmika I Ariyasinghe
- Tharaka L Dassanayake
- PubMed: 40789769
- DOI: 10.1017/s0007114525104169
Study Design
- Type
- Randomized Controlled Trial (RCT)
- Population
- 37 overnight sleep-deprived healthy adults (aged 22-30 years, twenty-one men)
- Methods
- Double-blind, placebo-controlled, counterbalanced, two-way crossover trial; acute effects of 200 mg L-theanine-160 mg caffeine combination on neurobehavioural and neurophysiological measures
- Blinding
- Double-blind
- Duration
- acute (single dose, effects measured 50 min after ingestion)
L-theanine, an amino acid found in tea, and caffeine, found in tea and coffee, are claimed to enhance attention. We conducted a double-blind, placebo-controlled, counterbalanced, two-way crossover trial to determine the acute effects of a high-dose L-theanine-caffeine combination on neurobehavioural (reaction time) and neurophysiological (P3b cognitive event-related potential (ERP)) measures of selective attention in acutely sleep-deprived healthy adults. Thirty-seven overnight sleep-deprived healthy adults (aged 22-30 years, twenty-one men) completed a computerised traffic-scene-related visual stimulus discrimination task before and 50 min after ingesting 200 mg L-theanine-160 mg caffeine combination or a placebo. The task involved selectively responding to imminent accident scenes (20 % probability) while ignoring randomly intermixed, more frequent safe scenes (80 % probability). A 32-channel electroencephalogram was recorded concurrently to derive ERP. The L-theanine-caffeine combination significantly improved the hit rate (P = 0·02) and target-distractor discriminability (P = 0·047), compared with the placebo. Although both L-theanine-caffeine combination (△ = 52·08 ms, P < 0·0001) and placebo (△ = 13·97 ms, P = 0·024) improved reaction time to accident scenes, the pre-post-dose reaction time improvement of the L-theanine-caffeine combination was significantly greater than that of placebo (△ = 38·1 ms, P = 0·003). Compared with the placebo, the L-theanine-caffeine combination significantly increased the amplitudes and reduced the latencies of P3b ERP component. Our findings suggest that L-theanine-caffeine combination improves the accuracy and speed of deploying selective attention to traffic scenarios in sleep-deprived individuals. This improvement is brought about by greater and faster neural resource allocation in the attentional networks of the brain.
Research Insights
The L-theanine-caffeine combination significantly improved the hit rate (P = 0·02)
- Effect
- Beneficial
- Effect size
- Small
- Dose
- 200 mg
target-distractor discriminability (P = 0·047)
- Effect
- Beneficial
- Effect size
- Small
- Dose
- 200 mg
the L-theanine-caffeine combination significantly increased the amplitudes of P3b ERP component
- Effect
- Beneficial
- Effect size
- Small
- Dose
- 200 mg
the L-theanine-caffeine combination significantly ... reduced the latencies of P3b ERP component
- Effect
- Beneficial
- Effect size
- Small
- Dose
- 200 mg
the pre-post-dose reaction time improvement of the L-theanine-caffeine combination was significantly greater than that of placebo (△ = 38·1 ms, P = 0·003)
- Effect
- Beneficial
- Effect size
- Large
- Dose
- 200 mg