Introduction the Importance of Sleep to a Sense of Well-being Is Evident to Anyone Who Has Spent a Sleepless

THE IMPORTANCE OF SLEEP TO A SENSE OF WELL-BEING IS EVIDENT TO ANYONE WHO HAS SPENT A SLEEPLESS NIGHT. However, the amount of sleep necessary for good health is unclear. Most sleep professionals, as well as the National Sleep Foundation, recommend that adults obtain 8 hours of sleep per night.1 However, with the increasing demands placed on individuals in Western society, the time adults in the United States spend asleep has steadily fallen. The average sleep duration among American adults in a recent poll was only 6.9 hours per night, and 39% of respondents slept less than 7 hours.1 The health effects of these changes in sleep habits are only beginning to be elucidated. Recent work suggests that beyond the deleterious neurocognitive effects of sleep restriction,2 a short-term reduction in sleep time may lead to increased sympathetic tone and worsened glucose tolerance.3 Epidemiologic studies suggest that those who sleep less may be at greater risk for developing cardiovascular disease and diabetes.4,5 An even more intriguing finding has been that increased time spent asleep may also result in adverse health outcomes. A recent, large, prospective study of American Cancer Society volunteers found an increased risk of death among those reporting sleeping more than 7 hours per night.6 The mechanism by which increased sleep results in a higher mortality risk is unclear. Although many confounders, such as amount of physical activity and degree of obesity, were adjusted for in this study, the effects of other factors, including depressed mood, alcohol consumption, snoring, and shift working, were not investigated. All of these variables have been associated with increased mortality risk, and all have the potential to affect sleep habits. We sought to more-closely investigate the effects of both short and long sleep duration on the risk of death using a large prospective cohort of women.