title: A dose-response relationship between short sleeping hours and childhood obesity: results of the Toyama Birth Cohort Study.
abstract: BACKGROUND
  Short sleeping hours could cause obesity through increased sympathetic activity, elevated cortisol secretion and decreased glucose tolerance. The aim of this study was to clarify parental and lifestyle factors, particularly sleeping habits, associated with obesity in Japanese children.
  
  
  METHODS
  Between June and July 1996, 8274 children (4194 males and 4080 females) aged 6-7 years living in Toyama prefecture, Japan, were investigated by questionnaire survey and the collection of anthropometric data. Subjects with a body mass index (BMI; weight in kg divided by square of height in m) greater than the age- and sex-specific cut-off points linked to adulthood overweight (BMI of 25 kg/m2 or more) were defined as obese subjects. Parental obesity was defined as a BMI of 25 kg/m2 or more. Logistic regression analysis was performed to evaluate the strength of the relationships between parental obesity or lifestyle factors and childhood obesity, adjusted for possible confounding factors.
  
  
  RESULTS
  Parental obesity, long hours of TV watching and physical inactivity were significantly associated with childhood obesity. Although wake-up time was not related to obesity, there was a significant dose-response relationship between late bedtime or short sleeping hours and childhood obesity. Compared with children with 10 or more hours of sleep, the adjusted odds ratio was 1.49 (95% confidence interval 1.08-2.14) for those with 9-10 h sleep, 1.89 (1.34-2.73) for those with 8-9 h sleep and 2.87 (1.61-5.05) for those with <8 h sleep, after adjustment for age, sex, parental obesity and other lifestyle factors.
  
  
  CONCLUSIONS
  A strong inverse association was observed in the relationship between sleeping hours and childhood obesity. Longitudinal research will be required to confirm this causality.
authors.affiliation: Department of Welfare Promotion and Epidemiology, Toyama Medical and Pharmaceutical University, Toyama City, Japan. sekine@ms.toyama-mpu.ac.jp
authors.forename: Michikazu
authors.initials: M
authors.lastname: Sekine
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamagami
authors.forename: Kyoko
authors.initials: K
authors.lastname: Handa
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Saito
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Nanri
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kawaminami
authors.forename: Noritaka
authors.initials: N
authors.lastname: Tokui
authors.forename: Katsumi
authors.initials: K
authors.lastname: Yoshida
authors.forename: Sadanobu
authors.initials: S
authors.lastname: Kagamimori
mesh_terms: D000886:Anthropometry; D002648:Child; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D003625:Data Collection; D015444:Exercise; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D009765:Obesity / Q000150:complications* / Q000378:metabolism; D012892:Sleep Deprivation / Q000150:complications* / Q000378:metabolism; D011795:Surveys and Questionnaires; D013690:Television / Q000706:statistics & numerical data