title: Habitual sleep variability, mediated by nutrition intake, is associated with abdominal obesity in adolescents.
abstract: OBJECTIVE
  To investigate habitual sleep duration (HSD) and habitual sleep variability (HSV) in relation to abdominal obesity and nutrient intake as mediating factors in adolescents.
  
  
  METHODS
  We analyzed data from 305 adolescents who participated in the Penn State Child Cohort follow-up examination. An actigraphy device was used for seven consecutive nights to calculate HSD and HSV. Abdominal obesity was assessed by dual-energy x-ray absorptiometry. The Youth/Adolescent Food Frequency Questionnaire was used to obtain daily total caloric, protein, fat, and carbohydrates intakes. Linear regression models were used to associate HSD and HSV with abdominal obesity and to qualitatively identify mediating factors. The mediating effect was quantitatively estimated by mediation models.
  
  
  RESULTS
  After adjusting for major covariates and HSD, higher HSV was significantly associated with abdominal obesity measures. For example, with 1-hour increase in HSV, android/gynoid fat ratio and visceral fat area increased by 0.02 cm(2) (standard error = 0.01, p = 0.03) and 6.86 cm(2) (standard error = 2.82, p = 0.02), respectively. HSD was not associated with abdominal obesity in HSV-adjusted models. Total caloric, fat, and carbohydrate intakes were significant mediating factors. For instance, 20% of the association between HSV and visceral fat can be attributed to carbohydrate intake.
  
  
  CONCLUSIONS
  Higher HSV, not HSD, is significantly associated with abdominal obesity, which can be partially explained by increased caloric intake, especially from carbohydrate, in adolescents. This study suggests that more attention should be paid to establish and maintain regular sleep patterns in adolescents.
authors.affiliation: Department of Public Health Sciences, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: He
authors.affiliation: Sleep Research and Treatment Center, Department of Psychiatry, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Edward O
authors.initials: EO
authors.lastname: Bixler
authors.affiliation: Department of Public Health Sciences, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Jiangang
authors.initials: J
authors.lastname: Liao
authors.affiliation: Department of Public Health Sciences, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Arthur
authors.initials: A
authors.lastname: Berg
authors.affiliation: Institute for Personalized Medicine, Departments of Biochemistry and Molecular Biology and Pharmacology, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Imamura Kawasawa
authors.affiliation: Sleep Research and Treatment Center, Department of Psychiatry, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Julio
authors.initials: J
authors.lastname: Fernandez-Mendoza
authors.affiliation: Sleep Research and Treatment Center, Department of Psychiatry, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Alexandros N
authors.initials: AN
authors.lastname: Vgontzas
authors.affiliation: Department of Public Health Sciences, The Pennsylvania State University College of Medicine, Hershey, PA, USA. Electronic address: dliao@psu.edu.
authors.forename: Duanping
authors.initials: D
authors.lastname: Liao
mesh_terms: D056044:Actigraphy; D000293:Adolescent; D015992:Body Mass Index; D015331:Cohort Studies; D020920:Dyssomnias / Q000150:complications* / Q000503:physiopathology; D002149:Energy Intake / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D008297:Male; D056128:Obesity, Abdominal / Q000209:etiology*; D012890:Sleep / Q000502:physiology*; D011795:Surveys and Questionnaires
keywords: Abdominal obesity; Nutrition intake; Sleep variability