title: Association between sleep duration, weight gain, and obesity for long period.
abstract: BACKGROUND
  Although previous studies showed the long-term effects of sleep duration on risk of weight gain, Western tends to gain weight irrespective of sleep duration over a long period. Conversely, it is showed that body mass index (BMI) decreases during a long period in Japanese and thus, the long-term effect of sleep duration on weight gain and obesity is still unclear in Asia.
  
  
  METHODS
  We followed up 13,629 participants aged 40-79years and prospectively collected data from 1995 to 2006. We divided the participants into five groups according to their self-reported sleep duration: ⩽5h (short sleep), 6h, 7h (reference), 8h, and ⩾9h (long sleep). The main outcome was ⩾5kg weight gain or BMI⩾25kg/m(2) (obesity). We used logistic regression analyses to derive odds ratios (ORs) and 95% confidence intervals (CIs), adjusted for several confounding factors.
  
  
  RESULTS
  We observed no association between sleep duration and risk of ⩾5kg weight gain and obesity. After stratification by BMI, long sleepers had a significantly increased risk of ⩾5kg weight gain (OR: 1.36, 95%CI: 1.09-1.70) in obese participants.
  
  
  CONCLUSIONS
  Among community-dwelling Japanese, only obese long sleepers have a significantly increased long-term risk of ⩾5kg weight gain.
authors.affiliation: Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. m-nagai@med.tohoku.ac.jp
authors.forename: Masato
authors.initials: M
authors.lastname: Nagai
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Tomata
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Masako
authors.initials: M
authors.lastname: Kakizaki
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tsuji
mesh_terms: D000328:Adult; D000368:Aged; D016001:Confidence Intervals; D003431:Cross-Cultural Comparison; D006970:Disorders of Excessive Somnolence / Q000453:epidemiology / Q000208:ethnology; D005260:Female; D006801:Humans; D007564:Japan; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000208:ethnology; D016017:Odds Ratio; D011446:Prospective Studies; D012307:Risk Factors; D012892:Sleep Deprivation / Q000453:epidemiology* / Q000208:ethnology; D015430:Weight Gain