title: J-curve relation between daytime nap duration and type 2 diabetes or metabolic syndrome: A dose-response meta-analysis.
abstract: Adequate sleep is important for good health, but it is not always easy to achieve because of social factors. Daytime napping is widely prevalent around the world. We performed a meta-analysis to investigate the association between napping (or excessive daytime sleepiness: EDS) and the risk of type 2 diabetes or metabolic syndrome, and to quantify the potential dose-response relation using cubic spline models. Electronic databases were searched for articles published up to 2016, with 288,883 Asian and Western subjects. Pooled analysis revealed that a long nap (≥60 min/day) and EDS were each significantly associated with an increased risk of type 2 diabetes versus no nap or no EDS (odds ratio 1.46 (95% CI 1.23-1.74, p < 0.01) for a long nap and 2.00 (1.58-2.53) for EDS). In contrast, a short nap (<60 min/day) was not associated with diabetes (p = 0.75). Dose-response meta-analysis showed a J-curve relation between nap time and the risk of diabetes or metabolic syndrome, with no effect of napping up to about 40 minutes/day, followed by a sharp increase in risk at longer nap times. In summary, longer napping is associated with an increased risk of metabolic disease. Further studies are needed to confirm the benefit of a short nap.
authors.affiliation: Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan.
authors.forename: Tomohide
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Shojima
authors.affiliation: Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Yamauchi
authors.affiliation: Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kadowaki
mesh_terms: D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology*; D006801:Humans; D024821:Metabolic Syndrome / Q000209:etiology*; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D012890:Sleep / Q000502:physiology