title: The effects of sleep duration on the incidence of cardiovascular events among middle-aged male workers in Japan.
abstract: OBJECTIVE
  Although previous epidemiological studies have investigated the relationship between sleep duration and various cardiovascular events, the results have been inconsistent. Accordingly, we conducted a follow-up survey to investigate the relationship between sleep duration and cardiovascular events among male workers, accounting for occupational factors that might confound the true relationship.
  
  
  METHODS
  A total of 2282 male employees aged 35-54 years based in a factory in Japan were followed for 14 years. The risk of cardiovascular events was compared among 4 groups stratified based on sleep duration at baseline (<6, 6-6.9, 7-7.9, and ≥8 hours). Cardiovascular events included stroke, coronary events and sudden cardiac death. The hazard ratios for events were calculated using a Cox proportional hazards model, with the 7-7.9-hour group serving as a reference. The model was adjusted for potential confounders including traditional cardiovascular risk factors and working characteristics.
  
  
  RESULTS
  During 14 years of follow-up, 64 cardiovascular events were recorded including 30 strokes, 27 coronary events and 7 sudden cardiac deaths. After adjustment for possible confounders, the hazard ratios for cardiovascular and coronary events in the <6-hour group were 3.49 [95% confidence interval (95% CI) 1.30-9.40] and 4.95 (95% CI 1.31-18.73), respectively. There was no significant increment in the risk of stroke for any sleep duration groups.
  
  
  CONCLUSIONS
  Short sleep duration (<6 hours) was a significant risk factor for coronary events in a Japanese male working population.
authors.affiliation: Department of Epidemiology and Public Health, Kanazawa Medical University, Uchinada, Ishikawa, Japan. hamayu@kanazawa-med.ac.jp
authors.forename: Yuko
authors.initials: Y
authors.lastname: Hamazaki
authors.forename: Yuko
authors.initials: Y
authors.lastname: Morikawa
authors.forename: Koshi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Masaru
authors.initials: M
authors.lastname: Sakurai
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Miura
authors.forename: Masao
authors.initials: M
authors.lastname: Ishizaki
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Kido
authors.forename: Yuchi
authors.initials: Y
authors.lastname: Naruse
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Suwazono
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nakagawa
mesh_terms: D000328:Adult; D002318:Cardiovascular Diseases / Q000453:epidemiology*; D016757:Death, Sudden, Cardiac / Q000453:epidemiology; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016272:Occupational Health; D016016:Proportional Hazards Models; D012307:Risk Factors; D012890:Sleep; D020521:Stroke / Q000453:epidemiology; D011795:Surveys and Questionnaires