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 Jich 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.

BackgroundAlthough 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.MethodsThe 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.ResultsA 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.ConclusionsOur 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.

Communications. The people who moved out of the communities during the observation period were followed up until the date of the emigration. Data on emigration of the study subjects were obtained every year from their municipal governments.Age at menopause was categorized into <40 years, 40-44 years, 45-49 years, 50-54 years, and 55+ years. The reference group was females who were 45-49 years at menopause.Statistical analysis was performed using the SPSS ® software version 11.0. Descriptive parameters are shown as mean, standard deviation or proportion (%). We compared characteristics between the groups by one-way analyses of variance or the chisquare tests. Cox's proportional hazard models were used to calculate hazard ratios of mortality for age at menopause after adjusting for age, SBP, serum total cholesterol level, HDL cholesterol level, history of diabetes mellitus, BMI, smoking habits, alcohol drinking habits, marital status, study area, and type of menopause, which were considered to be potential confounding factors. Among the potential confounding factors that we obtained as the baseline data about blood pressure, we used SBP only in the multivariate analyses to avoid the co-linearity.This study was approved by the Institutional Review Board of Jichi Medical School for ethical issues.