Association between sleep quality and metabolic syndrome: A systematic review and meta-analysis.

Sleep quality has been suggested to play an important role in development of metabolic syndrome (MetS). However, the results have been inconsistent. A systematic review of observational studies aimed to evaluate the association between sleep quality and MetS. A comprehensive search was conducted in PubMed and EMBASE. The pooled odd ratios (ORs) were calculated using random effects models. The construction of funnel plot was used to explore publication bias, with further application of Egger's test. 22 studies were included. The pooled finding showed that overall sleep quality had a significant positive association with MetS (OR 1.37, 95% CI 1.15-1.64), with substantial heterogeneity (I2 = 62.4%, P < 0.1). Similarly, the complaints of sleep, including difficulty in falling sleep (OR 1.18, 95% CI 1.05-1.33), difficulty in maintaining sleep (OR 1.15, 95% CI 1.02-1.30) and sleep inefficiency (OR 1.40, 95% CI 1.04-1.89) were proved to be associated with the risk of MetS. Our results indicated the overall sleep quality as well as sleep complaints have significant positive associations with MetS. Further studies based on a longitudinal design using validated tools that measure both objective and subjective components of sleep quality are needed to explore the causal relationship between sleep quality and MetS.