title: Sleep duration and incidence of cardiovascular events in a Japanese population: the Jichi Medical School cohort study.
abstract: BACKGROUND
  Although sleep is one of the most important health-related factors, the relationship between sleep duration and the incidence of cardiovascular events has not been fully described.
  
  
  METHODS
  The present study comprised the 11,367 study subjects (4413 men and 6954 women) of the Jichi Medical School Cohort Study, a population-based prospective study. Baseline data were obtained by questionnaire and health examinations between April 1992 and July 1995 in 12 rural areas in Japan, and the main outcome measures were the incidence of cardiovascular diseases (stroke and myocardial infarction [MI]). Cox proportional hazards models were used to analyze the association between sleep duration and the incidence of cardiovascular events.
  
  
  RESULTS
  A total of 481carciovascular events (255 men and 226 women) were observed during an average follow-up period of 10.7 years. After adjusting for age, systolic blood pressure, serum total cholesterol, body mass index, smoking habits, and alcohol drinking habits, the hazard ratios (95% confidence intervals) for the incidence of cardiovascular diseases for individuals sleeping less than 6 hours and 9 hours or longer were 2.14 (1.11-4.13) and 1.33 (0.93-1.92) in men, and 1.46 (0.70-3.04) and 1.28 (0.88-1.87) in women, respectively, relative to those who reported sleeping 7 to 7.9 hours per day.
  
  
  CONCLUSIONS
  Our data indicate that men who sleep less than 6 hours a day have a higher risk of cardiovascular events than those sleeping 7 to 7.9 hours.
authors.affiliation: Division of Community and Family Medicine, Center for Community Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan. y.amagai@jichi.ac.jp
authors.forename: Yoko
authors.initials: Y
authors.lastname: Amagai
authors.forename: Shizukiyo
authors.initials: S
authors.lastname: Ishikawa
authors.forename: Tadao
authors.initials: T
authors.lastname: Gotoh
authors.forename: Kazunori
authors.initials: K
authors.lastname: Kayaba
authors.forename: Yosikazu
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Eiji
authors.initials: E
authors.lastname: Kajii
mesh_terms: D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000453:epidemiology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012423:Rural Health; D012737:Sex Factors; D012890:Sleep; D020521:Stroke / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D013997:Time Factors