Sleeping and waking up at different times is associated with an increased risk of heart attack and stroke, even for people who get the recommended amount of sleep, according to new research.
While most previous research has measured the impact of sleep length on human health, less is known about the effects of changes to the sleep cycle, said researchers in a statement published Tuesday.
To address this, for seven days scientists tracked activity data from 72,269 participants aged 40 to 79 who had never suffered a major adverse cardiovascular event.
They calculated each person’s Sleep Regularity Index (SRI) score, with higher scores denoting more regular sleepers.
The team then tracked incidents of cardiovascular death, heart attack, heart failure and stroke over eight years and found that irregular sleepers were 26% more likely to suffer one of these events than those with a regular sleep cycle. Irregular sleep means the variations in the time someone goes to sleep and wakes up.
The 26% calculation also takes into account a number of factors, including age, physical activity, alcohol consumption and smoking that could have influenced the findings. However, it was an observational study and, as such, can only establish a link rather than cause and effect: we can’t know for sure if irregular sleep patterns caused the increased risk.
Researchers also noted that those with a higher SRI score (more regular sleepers) were more likely to get the daily recommendation of seven to nine hours of sleep per night for 18-64 year olds, and seven to eight hours for those over the age of 65, with 61% of regular sleepers doing so compared to 48% of irregular sleepers.
But even those irregular sleepers who got the recommended amount of sleep had a higher risk of suffering a major cardiovascular event.
“Our results suggest that sleep regularity may be more relevant than sufficient sleep duration,” the study said.
As for reducing the risk of cardiovascular events, Chaput highlighted the fact that high blood pressure is a leading risk factor.
“Readers should prioritize seven to nine hours of consistent, restorative sleep per night, as poor sleep can contribute to high blood pressure,” he said.
“Bedtimes and wake-up times don’t need to be exactly the same every day, but it’s best to keep them within 30-60 minutes of your usual schedule to support your body’s natural circadian rhythm,” added Chaput.
“Small variations are fine, but consistent sleep patterns improve sleep quality, boost mood and cognitive function, and lower the risk of health issues like heart disease and diabetes,” he said.
Chaput also warned against relying on catching up on sleep at the weekends.
“It’s possible to recover some sleep by sleeping longer on weekends, but it doesn’t fully undo the negative effects of chronic sleep deprivation during the workweek,” he said.
“While extra weekend sleep can temporarily improve mood and cognitive function, irregular sleep patterns can disrupt your body’s circadian rhythm and lead to long-term health risks like obesity, diabetes and heart disease,” added Chaput, who is currently developing healthy sleep guidelines in collaboration with the World Health Organization.
“I believe it’s a crucial next step to ensure sleep is valued as an essential component of well-being, rather than dismissed as a waste of time in our society,” he said.
Naveed Sattar, a professor of cardiometabolic medicine at the University of Glasgow in Scotland, who was not involved in the research, said that while there are associations between the sleep cycle and cardiovascular health, the study used “overly causal” language.
“It’s very hard to say,” said Attar, adding that he “would be cautious in attributing causality here.”
The study was published in the Journal of Epidemiology & Community Health.