Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Nutrition Reviews systematic review of 50 RCTs (15 contributed to ≥1 random-effects SMD meta-analysis through Aug 2023) reports small-to-moderate acute cognitive/mood signals favouring theanine+caffeine versus placebo in the first two hours post-dose for several tasks, with wide confidence intervals; theanine alone showed a small-moderate choice reaction-time advantage versus placebo in hour 1.
Design
- Corpus: 50 RCTs in healthy adults; 15 trials entered ≥1 meta-analysis (Aug 2023 search)
- Interventions: tea, l-theanine, l-theanine + caffeine, vs placebo
- Endpoints: cognition, mood, sleep (sleep MA coverage is limited vs cognition arms—read forest plots)
Example acute SMDs vs placebo (abstract; hour-specific)
Theanine + caffeine vs placebo
- Choice reaction time (h1): SMD −0.48 (95% CI −1.01 to 0.05)
- Digit vigilance accuracy (h2): SMD 0.20 (0.02 to 0.38)
- Attention-switching accuracy (h2): SMD 0.33 (0.13 to 0.54)
- Overall mood (h2): SMD 0.26 (−0.10 to 0.63)
Theanine alone vs placebo
- Choice reaction time (h1): SMD −0.35 (−0.61 to −0.10)
Evidence hygiene
CIs often include null; acute lab tasks ≠ long-term clinical benefit; do not merge with titrated depression omega-3 trials or high-dose caffeine sleep work (Gardiner 2023) without reading arm definitions.
Publication
Payne ER, Bain JR, Nussbaumerova M, et al. Nutr Rev. 2025 Oct 1;83(10):1417–1446. PMID 40314930.
Outcomes
- Effect Size (Cohen's d / SMD)-0.35d (Cohen's d)
- Effect Size (Cohen's d / SMD)0.33d (Cohen's d)