The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 40056718 · doi:10.1016/j.smrv.2025.102076
What was done
Systematic review and meta-analysis of randomized controlled trials evaluating the effects of L-theanine supplementation on sleep outcomes across all ages and health statuses. Searches were conducted across five electronic databases (APA PsycINFO, CINAHL, Medline, Scopus, Web of Science) and the Cochrane Central Register of Controlled Trials from inception to September 2024. Nineteen articles (N = 897 participants) met inclusion criteria, with 18 included in quantitative meta-analysis.
What was found
L-theanine supplementation significantly improved subjective sleep onset latency (SMD = 0.15, 95% CI [0.01, 0.29], p = 0.04; n = 10 studies), subjective daytime dysfunction (SMD = 0.33, 95% CI [0.16, 0.49], p < 0.001; n = 9 studies), and overall subjective sleep quality score (SMD = 0.43, 95% CI [0.04, 0.83], p = 0.03; n = 12 studies).
Why it matters
This review provides quantitative evidence that L-theanine can modestly improve perceived sleep onset, daytime functioning, and overall subjective sleep quality.
Limits
The total sample across 19 trials was modest (897 participants, averaging ~47 per study). The abstract notes a scarcity of trials examining pure L-theanine, optimal dosing and duration remain undetermined, and objective sleep parameters were not reported.