If you regularly wake up and go to bed at different times, you could be at increased risk of heart attack and stroke.
According to new research in a health journal, sleep regularity, or how often you stick to the same sleeping and waking schedule, appears to be a stronger predictor of major cardiovascular events than sleep duration.
It is the first study of its kind to look at the effects of both sleep duration and sleep regularity on cardiovascular disease.
The authors found that the risk of heart attack, stroke, and heart failure all increased significantly in people with irregular sleep patterns, even if they got the recommended number of hours of sleep for their age.
Conversely, individuals who adhered most strongly to a regular sleep and wake schedule had a lower risk of major cardiovascular events.
“Sleep irregularity refers to frequently changing sleep schedules, like going to bed and waking up at different times each day, which can disrupt the body and negatively impact health. This research emphasizes the importance of prioritizing sleep regularity in public health guidelines and clinical care to support cardiovascular health.” researcher said.
Higher risk of cardiovascular event among irregular sleepers
The large study included more than 72,000 individuals between the ages of 40 and 79 with no history of major cardiovascular events.
All participants were part of the UK Biobank cohort, a biomedical database that includes de-identified data from half a million individuals in the United Kingdom.
Sleep is complex, so researchers attempted to control for a wide variety of factors that could affect the study’s outcomes, including age, sex, ethnicity, history of cardiovascular disease, and mental health. They also included important aspects of lifestyle that could affect sleep quality, such as self-reported sleep problems, whether or not the individual worked odd hours (night shifts), and even screen time.
Another strength of the study is that it did not rely on self-reported sleep data. Participants utilized activity trackers for seven days to record their sleep.
Based on the recorded sleep data, participants were given a “Sleep Regularity Index” (SRI) score; lower scores indicate irregular sleep patterns. Individuals in the cohort were further stratified according to their SRI score into three groups:
Regular: SRI of greater than 87.3
Moderately irregular: SRI of 71.6 to 87.3
Irregular: SRI of less than 71.6
The study found that irregular sleepers had a 26% increased risk of major cardiovascular events, and moderate irregular sleepers had a modest increase of 8%.
The next question for researchers was whether or not getting sufficient sleep could offset the risk of irregular sleep.
Unfortunately, they found that even getting the recommended number of hours wasn’t enough to reduce risk for irregular sleepers, but it did have an effect on those in the moderately irregular group.
“While both adequate sleep duration and regular sleep patterns are important, our findings show that meeting sleep duration recommendations alone does not eliminate the increased MACE risk for those with irregular sleep schedules,” said researcher.
In fact, regular sleep patterns were actually found to be protective against cardiovascular outcomes.
A minimum SRI score of 77.1 was associated with a 15% reduction in risk, with even greater benefit occurring with more regular sleep: an SRI of 80.8 yielded an 18% reduction.
Dangers of irregular sleep-wake cycles
While research has tended to focus on sleep duration, sleep regularity has consistently been linked to a host of negative health outcomes.
A 2023 study published in Sleep found that sleep regularity was a stronger predictor of overall mortality risk than sleep duration. Participants with higher SRI scores had as much as a 48% lower risk of all-cause mortality than those with the lowest SRI scores.
Andrew J. K. Phillips, MD, a sleep scientist and associate professor at the Flinders University College of Medicine and Public Health, was the senior author of that study.
He said, that this novel research on cardiovascular outcomes is consistent with his own research.
“There is a strong emerging body of evidence from not only my group but many research groups around the world showing that irregular sleep patterns are bad for our health. What we are seeing is that sleep regularity is not just a predictor of one area of health, but rather it seems to touch on a wide range of health outcomes, from mortality to diabetes to mental health,” Phillips said.
Phillips also authored a 2017 study that irregular sleeping was associated with poorer academic performance.
“Irregular sleep patterns likely lead to disruption of the body’s network of circadian (24-hour) clocks. These clocks regulate the timing of all kinds of physiological functions throughout the body, including cell metabolism,” he said.
