Efficacy of dietary supplements on improving sleep quality: a systematic review and meta-analysis.

PURPOSE: Different dietary supplements aimed at improving sleep quality are available on the market, but there has not been a comprehensive review to evaluate the efficacy of these dietary supplements on subjective sleep quality. We aimed to summarise up-to-date research evidence and to identify the types of dietary supplement that improve subjective sleep quality.

METHODS: Multiple databases (Ovid Emcare, Ovid MEDLINE (R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and APA PsycInfo) were used for searching papers published until August 2020. The changes in sleep quality indices, intervention duration and sample size were extracted from every paper. To analyse the effect of dietary supplements on sleep quality, a random effects model with mean difference (MD) and 95% CI was adopted. The heterogeneity across studies was measured by I2 statistics. The quality of included studies was evaluated by Cochrane's risk of bias tool.

RESULTS: Thirty-one randomised controlled trials of dietary supplements were included. Subjective sleep quality was significantly improved by supplementation of amino acids (MD -1.27, 95% CI -2.35 to -0.20; I2 =0%), melatonin (MD -1.21, 95% CI -2.17 to -0.24; I2 =79%) and vitamin D (MD -1.63, 95% CI -3.15 to -0.10; I2 =85%). Although not all studies provided adequate data for meta-analysis, we also discussed how magnesium, zinc, resveratrol and nitrate supplementation may improve sleep quality.

CONCLUSIONS: Amino acids, vitamin D and melatonin supplements were significantly beneficial to improve sleep quality. However, high heterogeneity and wide confidence levels were observed in vitamin D and melatonin. Further research on the effect of magnesium, zinc, resveratrol and nitrate supplementation on improving sleep quality is required.