The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression

Context: L-tryptophan (Trp) has been documented to aid sleep, but a systematic compilation of its effect on sleep quality is still limited. Objective: We assessed the effect of Trp supplementation on sleep quality via meta-analysis and metaregression. The effects of daily Trp dose (<1 g and >= 1 g) were also assessed. Data sources: A database search was done in PubMed, Medline (Ovid), Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Cochrane and a total of 18 articles were collected. Data extraction: Extracted data from 4 articles were also analyzed using random-effect meta-analysis and meta-regression. Standardized mean difference (SMD) was used in meta-analysis. Data analysis: Results from the study suggested that Trp supplementation can shorten wake after sleep onset (-81.03 min/g, P = 0.017; SMD, -1.08 min [95%CI, -1.89 to -0.28]). In addition, the group receiving >= 1 g Trp supplementation had a shorter wake after sleep onset than the group with Trp < 1g supplementation (Trp <1 g vs Trp >= 1 g: 56.55 vs 28.91 min; P = 0.001). However, Trp supplementation did not affect other sleep components. Conclusion: Trp supplementation, especially at >= 1 g can help improve sleep quality.