There is ample evidence supporting the idea that getting enough sleep is great for your heart. However, according to new research, keeping heart disease at bay isn’t just about how much sleep you are getting—it also has to do with when you go to sleep. A study published November 9 in the European Heart Journal—Digital Health, a journal of the European Society of Cardiology (ESC), found that going to bed between the hours of 10:00 and 11:00 pm reduces the risk of developing heart disease compared to earlier or later bedtimes. In a press release accompanying the research, study author Dr. David Plans of the University of Exeter, UK explains that it all comes down to circadian rhythm, the body’s 24-hour internal clock responsible for regulating mental and physical function. “While we cannot conclude causation from our study, the results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health,” he said. Researchers collected from 88,026 individuals in the UK during a seven-day period between the years 2006 and 2010. They followed up with the group an average of 5.7 years later to monitor the incidence of non-fatal cardiovascular events, including heart attacks, heart failure, ischemic heart disease, stroke and transient ischemic attacks. 3,172 participants, or 3.6% of the group, developed cardiovascular disease. “The ‘sweet spot’ for lower risk was found for 10:00 to 11:00 pm,” explains Dr. Kim Smolderen, PhD, clinical psychologist, associate professor and co-director of Vascular Medicine Outcomes (VAMOS) Program at Yale School of Medicine. The highest risk group, those who went to sleep at midnight or later, were 25% more likely to develop cardiovascular disease than those with a sleep onset of 10:00 to 10:59 pm, followed by those who went to sleep prior to 10:00 pm with a 24% greater risk. Finally, those who went to sleep from 11:00 to 11:59 pm experienced a 12% raised risk.
What these findings mean
“These findings were found, even while adjusting for sleep duration, sleep irregularity and established cardiovascular disease risk factors,” adds Dr. Smolderen, who also notes that a stronger association was found for women than men. However, she does emphasize that while the association between chronic poor sleep quality and sleep deprivation and incident cardiovascular disease has certainly been well established, and the findings fit within those prior findings, the study was observational only, and “the risk for unmeasured confounding remains.” “For example, people who have typical sleep times after 12:00 am may also engage in other behaviors that may predispose them to higher cardiovascular risk, or there may be other underlying conditions or risk factors in those with very early or very late sleeping onset times that were not measured that can be alternative explanations for individuals’ increased risk,” she explains. Furthermore, occupational data was available, but the timeline of the measurement was years before the sleep data were collected and no stress or alcohol use data was available either. Lastly, the studied cohort was predominantly white and more affluent, and may not be generalizable to the overall population, she notes. “So collectively, while certainly thought-provoking and hypothesis-generating, there are several individual factors that remain unknown or unmeasured which may form alternative explanations for the association described, and potential generalizability concerns require further replication of these results,” she explains. “The study is a good reminder, though, that good sleep habits and quality may act as buffers for stress, and cardiovascular health.” Dr. Darren P. Mareiniss, MD, FACEP, Assistant Professor of Emergency Medicine, Sidney Kimmel Medical College - Thomas Jefferson University in Philadelphia, PA, agrees. “Prior studies have shown that later bedtimes correlate with obesity. This current study simply shows that sleep onset and bedtimes may be linked with cardiovascular disease,” he explains. However, he also points out that there are many potential confounders in the data. “This study does not provide proof that a specific bedtime causes better heart health. The authors, in their discussion, admit this and state that ‘[a]lthough the findings of this article do not show causality, they mandate further research into sleep timing as an independent cardiac risk factor, particularly for women.’ As the authors note, this requires further study,” he notes. Dr. Alcibiades Rodriguez, MD, Director of the Comprehensive Epilepsy Center—Sleep Center, NYU Langone Health, expresses the same concerns. “Are people with regular sleep schedules healthier or because they are healthier, follow a better schedule?” he says, questioning the observational study. “Even it was adjusted for some risk factors, it may not adjust for all.” Next up: 13 Tips for Improving Sleep
Sources
European Heart Journal Digital Health: Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort studyEuropean Society of Cardiology: Bedtime linked with heart healthDarren P. Mareiniss, MD, FACEP, Assistant Professor of Emergency Medicine, Sidney Kimmel Medical College - Thomas Jefferson UniversityKim Smolderen, PhD, clinical psychologist, associate professor and co-director Vascular Medicine Outcomes (VAMOS) Program at Yale School of MedicineAlcibiades Rodriguez, MD, Director of the Comprehensive Epilepsy Center – Sleep Center, NYU Langone Health
