Longer sleep duration, especially if it includes daytime napping, is associated with increased cardiovascular (CV) risk and mortality, suggests new research that also saw the risks go up with a sleep duration of less than 6 hours a day. An analysis from the PURE study estimated total daily sleep time, considering both overnight sleeping and daytime naps, in more than 116,000 participants from around the world over a follow-up of about 8 years. Both too little and too much sleep (less than 6 hours a day and more than 8 hours a day, respectively) were associated with increased risk for death and major cardiovascular events. "We observed a J-shaped association between the estimated total daily sleep duration and mortality and major cardiovascular events," state the authors of the report, led by Chuangshi Wang, doctoral candidate at McMaster University, Hamilton, Ontario, Canada, published online December 5 in the European Heart Journal. The association was significant after adjustment for demographic factors, lifestyle behaviors, and health status. Interestingly, napping by itself was associated with increased CV risk except in people with reduced night-time sleep. On the basis of the current study, "the optimal sleep duration appears to be 6–8 hours a day. Longer or shorter durations potentially expose us to increased CV risk," write Dominik Linz, MD, PhD, University of Adelaide and Royal Adelaide Hospital, Australia, and associates in an accompanying editorial. "Additionally, daytime napping, particularly among those with adequate duration of nocturnal sleep, might be an early indicator of poorer health and help identify those at higher risk of CV disease and mortality. Therefore, in clinical practice, assessment of sleep patterns may be of value in identifying higher risk individuals." The findings "make sense because those individuals who slept 6 to 8 hours likely had a restful sleep, while daytime napping is a sign of interrupted or nonrestful sleep," Nieca Goldberg, MD, NYU Langone Medical Center, New York City, told theheart.org | Medscape Cardiology. What is important is "not only the number of hours you sleep, but if it is good quality sleep," said Goldberg, an American Heart Association volunteer expert not connected to the study. Not Too Little, Not Too Much Sleep is "increasingly regarded as an important lifestyle behavior that can affect cardiovascular disease (CVD) and death," the authors write. Insufficient sleep is associated with adverse health outcomes. And although some research suggests that people who get excessive amounts of sleep are at greater risk for CVD or death, other research has shown contradictory findings. For the current analysis, the researchers looked at data from the PURE cohort study, which involved people 35 to 70 years of age from 21 countries with different income levels. Participants initially filled out standardized questionnaires that assessed demographic characteristics, socioeconomic status, lifestyle behaviors, personal and family disease history, and medication use. Included were questions about day and night-time sleeping. Physical activity was assessed using the International Physical Activity Questionnaire, and dietary pattern was recorded using country- or region-specific food-frequency questionnaires. A total 7342 participants either died or had a major CV event during a median follow-up of 7.8 years. The latter end point included CV death, nonfatal myocardial Infarction, stroke, or heart failure. Participants with an estimated sleep duration of 6 hours per day or less had a higher body mass index (BMI) and waist-to-hip ratio, were less likely to consume alcohol, and were more likely to have diabetes. A larger number of participants who slept less than 6 hours or more than 8 hours reported symptoms of depression and at least one health condition. Six to 8 Hours a Day: Just Right? The median estimated total sleep duration per day in the population was 8.0 hours. Participants with an estimated sleep duration of 6 to 8 hours per day had the lowest incidences of all outcomes. Moreover, less than 6 hours or more than 8 hours of sleep per day was associated with a higher risk for major CV events, alone or as a composite of all-cause mortality, after adjustment for age, sex, and center. On its own, mortality risk was significantly elevated in those with longer sleep durations; in those with shorter sleep durations, the risk was elevated, but not significantly. Although the risk associations were "moderately attenuated" in the fully adjusted models, the researchers still found a J-shaped relation between estimated total sleep duration and each of the three outcomes. It was consistently observed in regions where daytime napping is common and where it is less common. The association for longer estimated sleep duration was only "slightly attenuated" when the researchers adjusted for BMI, physical activity, and diet. The results were similar in sensitivity analyses that excluded participants with disabilities, prevalent diseases, sleep apnea, sleep disorders, and shift workers, the analysis showed. With stratification by estimated nocturnal sleep duration (≤6 or >6 hours per night), the association between naps and increased risk for outcomes was observed only in those who slept at least 6 hours per at night, and not in those with a shorter duration of nocturnal sleep. "Daytime naps are associated with excessive risks of major cardiovascular events and deaths except in those with less nocturnal sleep suggesting that this may be a compensatory mechanism when nocturnal sleep is short," the group writes. Because the data in the current analysis are "associational, they do not necessarily imply a cause-and-effect relation," and therefore the findings "do not imply that simply adjusting sleep duration will impact mortality, although that association is possible," Karl Doghramji, MD, told theheart.org | Medscape Cardiology. "Sleepiness during the day may be a barometer or marker of mortality and should be looked at more closely in medical settings," said Doghramji, medical director, Jefferson Sleep Disorders Center at Thomas Jefferson University, Philadelphia, who was not involved with the study. Source
