Irregular Sleep-Wake Cycles Are Associated With Higher Disease Risk

Going to bed and waking up at different times each day may increase the risk of cardiovascular and metabolic illnesses, including heart disease and type 2 diabetes. So concludes the first study to consider the relationship between disease risk and a minute-by-minute measure of sleep regularity.

We spoke with the study’s lead author, Assistant Professor in Psychiatry and Behavioral Sciences at Duke University Jessica Lunsford-Avery, Ph.D., to learn more about the implications of this research.

The study, which was published in Scientific Reports, found that people with irregular sleep patterns tended to have higher blood sugar, higher blood pressure, and a higher projected risk of heart attack or stroke within the next decade compared to those with more regular sleep-wake cycles. Participants with irregular sleep cycles were also more likely to report stress and depression.

While previous research has found that extremely irregular sleep-wake cycles (such as those brought on by shift work or jet lag) are associated with poorer health outcomes, this study suggests sleep irregularity doesn’t need to be that severe in order to provoke ill effects.

“We have known for some time that individuals with extremely irregular sleep patterns — such as individuals engaged in rotating shift work — are at an elevated risk for heart and metabolic diseases,” Lunsford-Avery told Mattress Clarity via email. “What is novel about this study is that we used an extremely sensitive measure of sleep regularity — a minute-by-minute measure — so our findings suggest that even subtle changes in bed- and wake-times may have an impact on your health.”

What’s more, the research suggests that irregular sleep-wake cycles may be an even greater predictor of poor health outcomes than insufficient sleep.

RELATED: Too Little And Too Much Sleep Could Affect Heart Health

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Measuring Sleep Patterns Down To The Minute

Most people associate irregular sleep patterns with extreme scenarios such as shift work or jet leg. In reality, Lunsford-Avery says, “Irregular sleep patterns are actually quite common. For example, many individuals tend to go to sleep and wake up later on weekends than weekdays. Work schedules, family obligations, and leisure activities may all impact the regularity of sleep patterns.”

This study suggests even these subtle shifts in a person’s bed and wake times are associated with an increase in cardiometabolic risk.

Researchers from Duke Health and the Duke Clinical Research Institute worked with 1,978 adults who were enrolled in the Multi-Ethnic Study of Atherosclerosis (MESA). Participants ranged from ages 45 to 84 and fell into four racial/ethnic groups. All participants were free of cardiovascular disease and diagnosed sleep disorders at the time of the study.

Participants were asked to employ a number of testing methods, including devices that tracked sleep-wake cycles down to the minute, psychiatric health assessments, cardiometabolic health assessments, and self-reports relating to daytime sleepiness and bed- and wake-time preferences (e.g. night owls vs. morning larks).

The results suggested that irregular sleep patterns were often associated with going to bed later, but they were not necessarily equated with insufficient sleep quantity. Irregular sleep patterns were also linked with reduced physical activity, increased daytime sleepiness, reduced light exposure, and an increase in reported levels of stress and depression.

Perhaps most notably, the results suggest that the greater a person’s sleep irregularity, the higher their 10-year risk of developing heart disease, high blood pressure, obesity, diabetes, stroke, heart attack, and other indicators of cardiovascular and metabolic issues.

While these results are significant, so far they imply correlation and not causation.

“From our study we cannot definitively conclude that irregular sleep/wake patterns results in risk for heart disease and diabetes,” Lunsford-Avery says. “It may be that experiencing some of these risk factors… disrupts sleep regularity, or it could be a vicious cycle.”

She notes that there are several processes by which irregular sleep patterns may increase the risk of cardiometabolic disease — although whether this occurs directly or indirectly is not yet known. “For example, in our study, individuals with more irregular sleep/wake times tended to be less physically active, more stressed, and more depressed — all of which could contribute to poorer heart and metabolic health,” she says.

Still, more research is needed to determine exactly how irregular sleep patterns might be linked to cardiometabolic diseases. “Hopefully, future studies will clarify the processes linking irregular sleep patterns to risk for heart and metabolic illnesses,” Lunsford-Avery says.

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Improving Health Outcomes

Based on this study, the researchers suggest that measures of sleep regularity may be useful for predicting cardiometabolic risk.

“Researchers have known for some time that getting enough sleep is important to many aspects of human health,” Lunsford-Avery says. “What was interesting in our study is that sleep regularity was even more strongly associated with heart and metabolic risk factors than the length of sleep in this group of individuals. Sleep regularity was also unrelated to how long you sleep, meaning that even if you are getting “enough sleep” but at irregular times, you may still be at risk for these illnesses.”

Consequently, the study’s authors suggest that improving sleep regularity may offer one strategy for preventing and intervening in the advancement of cardiometabolic diseases. Says Lunsford-Avery, “Keeping your bedtimes and rise times as consistent as possible may be beneficial for supporting heart and metabolic health.”

[Editor’s Note: The content provided on this site is for general informational purposes only. Any information provided is not a substitute for professional medical advice. We encourage you to consult with the appropriate health expert if you have concerns.]

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Laura Newcomer

Laura Newcomer is the Editorial Controller at Mattress Clarity, where she occasionally writes sleep news. She's worked as a professional writer and editor for over a decade and has been published in or on outlets such as TIME, Washington Post, Inc., Entrepreneur, Huffington Post, Women's Health, and many more. Her primary areas of interest include sleep, fitness, nutrition, eco-friendly living, education, and all things wellness.

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