title: Self-reported sleep duration, all-cause mortality, cardiovascular mortality and morbidity in Finland.
abstract: OBJECTIVE
  The U-shaped association of self-reported sleep duration with all-cause mortality is generally accepted. Findings on cardiovascular (CVD) mortality and morbidity are inconsistent. We aimed to further clarify the associations of the self-reported sleep duration with CVD mortality and morbidity.
  
  
  METHODS
  In two population based surveys in 1972 and 1977 the levels of coronary risk factors in Finland and habitual sleep duration were measured; 25,025 individuals were followed-up until 2006 by the national register data. The outcome variables were death (for any reason), CVD death, and non-fatal CVD event (non-fatal myocardial infarction or stroke). Participants with former non-fatal CVD event at baseline were excluded from CVD analyses, and socio-demographic and health-related confounders were considered in the final Cox proportional hazard models for both genders.
  
  
  RESULTS
  The U-shaped association of total mortality with self-reported sleep duration was confirmed in both genders. The association of CVD mortality with self-reported sleep duration was independent of pertinent cardiovascular risk factors in women. The highest CVD mortality risk was found in both extreme ends of sleep duration distribution (⩽5 and ⩾10h sleepers).
  
  
  CONCLUSIONS
  Sleep duration is an independent risk factor for CVD mortality and morbidity in women but not in men. The highest CVD mortality risk is associated with the extreme ends of sleep duration distribution. Thus, in epidemiological studies, combining adjacent (6 and 9h) sleep duration groups with the extreme groups may partly mask the mortality risks, especially in the long run.
authors.affiliation: National Institute for Health and Welfare, Department of Chronic Disease Prevention, Turku, Finland. erkki.kronholm@thl.fi
authors.forename: Erkki
authors.initials: E
authors.lastname: Kronholm
authors.forename: Tiina
authors.initials: T
authors.lastname: Laatikainen
authors.forename: Markku
authors.initials: M
authors.lastname: Peltonen
authors.forename: Risto
authors.initials: R
authors.lastname: Sippola
authors.forename: Timo
authors.initials: T
authors.lastname: Partonen
mesh_terms: D000328:Adult; D002318:Cardiovascular Diseases / Q000401:mortality*; D003430:Cross-Sectional Studies; D016757:Death, Sudden, Cardiac / Q000453:epidemiology; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009017:Morbidity; D009203:Myocardial Infarction / Q000401:mortality; D016016:Proportional Hazards Models; D012307:Risk Factors; D057566:Self Report; D012890:Sleep; D012893:Sleep Wake Disorders / Q000401:mortality*; D020521:Stroke / Q000401:mortality; D013997:Time Factors