title: Daily sleep duration and risk of metabolic syndrome among middle-aged and older Chinese adults: cross-sectional evidence from the Dongfeng-Tongji cohort study.
abstract: BACKGROUND
  Evidence from epidemiological studies has demonstrated that a shorter or longer duration of nighttime sleep may increase the risk of metabolic syndrome. Little is known about the association between daily sleep duration, including nighttime sleep and daytime napping duration, and metabolic syndrome. We aimed to examine the association between daily sleep duration and metabolic syndrome and its components in middle-aged and older Chinese adults using data from the Dongfeng-Tongji Cohort study.
  
  
  METHODS
  A total of 25,184 participants (mean age 63.6 years) who completed the baseline questionnaire, physical examination and laboratory tests were included in this analysis. Daily sleep duration was calculated by summing up nighttime sleep duration and daytime napping duration. The metabolic syndrome was defined using the International Diabetes Federation criteria. Logistic regression models were used to investigate the association between daily sleep duration and the risk of metabolic syndrome and its components.
  
  
  RESULTS
  Of the participants, 8,046 (31.9%) had metabolic syndrome. Females had a higher prevalence (38.6%) of metabolic syndrome than males (23.9%). Female participants with longer daily sleep duration (≥8 hours, all P < 0.05) per day had a higher risk of metabolic syndrome compared with those sleeping 7-7.9 hours, adjusting for potential confounders. Longer daily sleep was positively associated with individual components of metabolic syndrome except central obesity in females, and was only positively associated with HDL-C in males. Further analysis revealed that a longer duration of daytime napping (≥90 minutes, P < 0.05) was associated with the risk of metabolic syndrome in females. However, nighttime sleep duration was not associated with the risk of metabolic syndrome in either males or females.
  
  
  CONCLUSIONS
  Our findings suggested that longer daytime napping duration rather than nighttime sleeping duration was associated with increased risk of metabolic syndrome in females. The findings have significant implications for further studies to explore the appropriate sleep duration for middle-aged and older adults.
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. wujing038913@163.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. wujing038913@163.com.
authors.forename: Jing
authors.initials: J
authors.lastname: Wu
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. xuguiqiang8906@163.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. xuguiqiang8906@163.com.
authors.forename: Guiqiang
authors.initials: G
authors.lastname: Xu
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. shenyi611613@163.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. shenyi611613@163.com.
authors.forename: Lijun
authors.initials: L
authors.lastname: Shen
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. zhangyanmei1229@gmail.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. zhangyanmei1229@gmail.com.
authors.forename: Yanmei
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. sll1234@126.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. sll1234@126.com.
authors.forename: Lulu
authors.initials: L
authors.lastname: Song
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. 1073474860@qq.com.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. 1073474860@qq.com.
authors.forename: Siyi
authors.initials: S
authors.lastname: Yang
authors.affiliation: Dongfeng General Hospital, Dongfeng Motor Corporation and Hubei University of Medicine, Daling Road 16, Shiyan, 442000, Hubei, China. yanghand@139.com.
authors.forename: Handong
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Social Medicine, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. liangyuan217@163.com.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liang
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. Wut@mails.tjmu.edu.cn.
authors.forename: Tangchun
authors.initials: T
authors.lastname: Wu
authors.affiliation: MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. wangyoujie@mails.tjmu.edu.cn.|Department of Maternal and Child Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Hangkong Road 13, Wuhan, 430030, Hubei, China. wangyoujie@mails.tjmu.edu.cn.
authors.forename: Youjie
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000368:Aged; D044466:Asian People; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D003920:Diabetes Mellitus; D005260:Female; D006801:Humans; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology*; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D015995:Prevalence; D012307:Risk Factors; D012737:Sex Factors; D012890:Sleep; D013997:Time Factors