title: Gender differences in nighttime sleep and daytime napping as predictors of mortality in older adults: the Rancho Bernardo study.
abstract: OBJECTIVE
  Many studies suggest optimal sleep duration for survival is 7-8h/night. We report the gender-specific independent association of all-cause mortality with nighttime sleep and daytime nap duration in older adults who were followed for up to 19years.
  
  
  METHODS
  Between 1984 and 1987, 2001 community-dwelling, mostly retired, adults (1112 women), age 60-96years, answered questions about health, mood, medications, life-style, daytime napping, and nighttime sleep duration. Vital status was confirmed for 96% through July 2001.
  
  
  RESULTS
  At baseline, men reported significantly longer nighttime sleep and daytime napping than women. In both men and women, nighttime sleep <6h was associated with depressed mood and sleep-related medication, and ⩾9h was associated with more alcohol consumption. Napping ⩾30min was associated with prevalent depressed mood, coronary heart disease, and cancer. Of the group, 61% died over the next 19years, at an average age of 85.6years. Mortality risk was lowest among those sleeping 7-7.9h/night in both men and women. Multiple-adjusted analyses showed that increased mortality was associated with nighttime sleep ⩾9h in women (HR 1.51: 95% CI=1.05-2.18), and with daytime napping ⩾30min in men (HR 1.28: 95% CI, 1.00-1.64).
  
  
  CONCLUSIONS
  Mechanisms for these differences are unknown.
authors.affiliation: Division of Epidemiology, Department of Family and Preventive Medicine, University of California, San Diego, La Jolla, CA 92093-0607, United States.
authors.forename: Kyu-In
authors.initials: KI
authors.lastname: Jung
authors.forename: Chan-Hee
authors.initials: CH
authors.lastname: Song
authors.forename: Sonia
authors.initials: S
authors.lastname: Ancoli-Israel
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Barrett-Connor
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D012307:Risk Factors; D012737:Sex Factors; D012890:Sleep / Q000502:physiology; D013997:Time Factors