New research suggests that varying sleep timing, particularly at weekends, could be an early warning sign for serious heart conditions including stroke and heart failure. The study, presented at the American Heart Association's Scientific Sessions 2026 in Chicago, has not yet been peer-reviewed.
Experts found that changing the time you go to bed, such as staying up late on weekends, could be detrimental to health. Varying the length of sleep too much, such as having a long lie-in or skipping going to bed, may also have a negative effect.
Study of Over One Million Nights of Sleep
The research analysed data from more than one million nights of sleep and concluded that maintaining a consistent sleep schedule may be an important factor in protecting the heart. Researchers analysed sleep data from more than 10,000 adults who wore an activity tracking device as part of the National Institutes of Health's All of Us research programme.
The study examined sleep quantity (total hours slept each night), sleep quality (time spent in light, deep and REM sleep), and how long a person was awake after first falling asleep. Researchers also looked at whether sleep duration, bedtime and wake-up time changed from night to night over around six months, as well as usual sleep and wake times, and any indications of a natural tendency to be a night owl or early bird.
Key Findings on Heart Risks
The results showed that changes in sleep timing from night to night over about a six-month period were linked to a 20%-23% higher risk of serious issues, including heart attack, stroke and heart failure. Every 29-minute increase in how much a person's sleep length varied from night to night was also linked with a higher risk, including a 29% higher risk of having a disease of the heart muscle, which leaves the heart unable to pump enough blood through the body, and a 20% higher risk of heart failure.
Having a greater number of complete "sleep cycles" each night led to a 28% lower risk of atrial arrhythmia, a common type of irregular heartbeat. In contrast, an unusually long sleep cycle was linked to a 55% higher risk of heart attack or stroke.
Expert Comment and Study Details
Lead researcher Dr Nguyen Minh Tuan Viet, a neuroscientist and postdoctoral research fellow at Boston Children's Hospital and Harvard Medical School in the US, said: "While we often focus on getting a full eight hours of sleep every night, having a regular sleep schedule – consistent bedtimes, wake times, and sleep duration from night to night – is a practical, actionable step anyone can take that may help protect their heart and blood vessels."
Dr Viet added: "Sleep irregularity is often due to weekends – we get to sleep a little bit later on a Friday night; or people have shift work. This may not be good for your heart health. Sometimes the quality of sleep is something we cannot control. But the regularity, consistent bedtimes throughout the week and waking up at the same time every morning, is something some people can control."
People in the study had an average age of 53, and about seven in 10 were women. None had heart or metabolic disease at the start of the study. Sleep was tracked for around six months and then people were followed for almost four years to see if they suffered heart issues.
