Gender differences in nighttime sleep and daytime napping as predictors of mortality in older adults: The Rancho Bernardo Study

Objective: Many studies suggest optimal sleep duration for survival is 7-8. h/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 19. years. Methods: Between 1984 and 1987, 2001 community-dwelling, mostly retired, adults (1112 women), age 60-96. years, 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 <6. h was associated with depressed mood and sleep-related medication, and ≥9. h was associated with more alcohol consumption. Napping ≥30. min was associated with prevalent depressed mood, coronary heart disease, and cancer. Of the group, 61% died over the next 19. years, at an average age of 85.6. years. Mortality risk was lowest among those sleeping 7-7.9. h/night in both men and women. Multiple-adjusted analyses showed that increased mortality was associated with nighttime sleep ≥9. h in women (HR 1.51: 95% CI = 1.05-2.18), and with daytime napping ≥30. min in men (HR 1.28: 95% CI, 1.00-1.64). Conclusions: Mechanisms for these differences are unknown.