Sleep duration and mortality in Japan: the Jichi Medical School Cohort Study

J Epidemiol. 2004 Jul;14(4):124-8. doi: 10.2188/jea.14.124.


Background: Although sleep is one of the most important health-related factors, relationship between sleep duration and mortality has not been fully discussed.

Methods: Study subjects were 11,325 participants (4,419 males and 6,906 females) in the Jichi Medical School Cohort Study, a population-based prospective study. Baseline data were obtained by questionnaire and health checkups between April 1992 and July 1995 in 12 rural areas in Japan. Main outcome measures were all-cause and cause-specific mortality derived from death certificates up to December 31, 2001. Cox's proportional hazard models were applied to analyze the association of sleep duration with mortality.

Results: A total of 495 deaths (289 males and 206 females) were observed during the average of 8.2-year follow-up period. After adjusting for age, systolic blood pressure, serum total cholesterol, body mass index, smoking habits, alcohol drinking habits, education, and marital status, the hazard ratios (95% confidence intervals) of all-cause mortality for individuals sleeping shorter than 6 hours and 9 hours or longer were 2.4 (1.3-4.2) and 1.1 (0.8-1.6) in males, and 0.7 (0.2-2.3) and 1.5 (1.0-2.4) in females, respectively, relative to those with 7-7.9 hours sleep.

Conclusion: Our data suggest that males with short sleep and females with long sleep were at an elevated risk of death.

MeSH terms

  • Adult
  • Female
  • Humans
  • Japan / epidemiology
  • Male
  • Middle Aged
  • Mortality / trends*
  • Proportional Hazards Models
  • Prospective Studies
  • Risk Factors
  • Schools, Medical
  • Sleep / physiology*
  • Surveys and Questionnaires
  • Time Factors