title: Sleep duration and incidence of colorectal cancer in postmenopausal women.
abstract: BACKGROUND
  Sleep duration is dependent on circadian rhythm that controls a variety of key cellular functions. Circadian disruption has been implicated in colorectal tumorigenesis in experimental studies. We prospectively examined the association between sleep duration and risk of colorectal cancer (CRC).
  
  
  METHODS
  In the Women's Health Initiative Observational Study, 75 828 postmenopausal women reported habitual sleep duration at baseline 1993-1998. We used Cox proportional hazards regression model to estimate the hazard ratio (HR) of CRC and its associated 95% confidence interval (CI).
  
  
  RESULTS
  We ascertained 851 incident cases of CRC through 2010, with an average 11.3 years of follow-up. Compared with 7 h of sleep, the HRs were 1.36 (95% CI 1.06-1.74) and 1.47 (95% CI 1.10-1.96) for short (≤5 h) and long (≥9 h) sleep duration, respectively, after adjusting for age, ethnicity, fatigue, hormone replacement therapy (HRT), physical activity, and waist to hip ratio. The association was modified by the use of HRT (P-interaction=0.03).
  
  
  CONCLUSIONS
  Both extreme short and long sleep durations were associated with a moderate increase in the risk of CRC in postmenopausal women. Sleep duration may be a novel, independent, and potentially modifiable risk factor for CRC.
authors.affiliation: Houston VA Health Services Research Center of Excellence, Michael E. DeBakey VA Medical Center, Houston, TX, USA. jiao@bcm.edu
authors.forename: L
authors.initials: L
authors.lastname: Jiao
authors.forename: Z
authors.initials: Z
authors.lastname: Duan
authors.forename: H
authors.initials: H
authors.lastname: Sangi-Haghpeykar
authors.forename: L
authors.initials: L
authors.lastname: Hale
authors.forename: D L
authors.initials: DL
authors.lastname: White
authors.forename: H B
authors.initials: HB
authors.lastname: El-Serag
mesh_terms: D002940:Circadian Rhythm; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause; D011446:Prospective Studies; D012306:Risk; D012890:Sleep; D020178:Sleep Disorders, Circadian Rhythm