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Irregular sleep — such as inconsistent sleep duration or sleep timing — may increase the risk of developing atherosclerosis among adults older than age 45, a new report suggests.
In particular, variation in sleep duration of more than 2 hours per night in the same week was tied to higher rates of atherosclerosis.
“Poor sleep is linked with several cardiovascular conditions, including heart disease, hypertension, and type 2 diabetes,” lead author Kelsie M. Full, PhD, MPH, assistant professor of medicine at Vanderbilt University Medical Center, told theheart.org | Medscape Cardiology.
“Overall, we found that participants who slept varying amounts of hours throughout the week (meaning that one night they slept less, one night they slept more) were more likely to have atherosclerosis than participants who slept about the same amount of time each night,” she said.
The study was published online February 15 in the Journal of the American Heart Association.
Full and colleagues examined data from 2032 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) Sleep Ancillary Study, which included adults between the ages of 45 and 84 years in six US communities who completed 7-day wrist actigraphy assessment and kept a sleep diary between 2010 and 2013.
For subclinical markers of cardiovascular disease, participants underwent assessments of coronary artery calcium, carotid plaque presence, carotid intima-media thickness, and ankle-brachial index.
The research team assessed sleep duration, or the total number of minutes of sleep in a night, and sleep timing regularity, which was determined on the basis of the time someone initially fell asleep each night. They adjusted for cardiovascular disease risk factors and sleep characteristics, such as obstructive sleep apnea, sleep duration, and sleep fragmentation.
The average age of the participants was 68.6 years, and 53.6% were women. About 37.9% identified as White, 27.6% as Black or African American, 23.4% as Hispanic American, and 11.1% as Chinese American.
During the 7-day period, about 38% of participants experienced a change in sleep duration of more than 90 minutes, and 18% experienced a sleep duration change of more than 120 minutes. Those who had irregular sleep were more likely to be non-White, current smokers, have lower average annual incomes, have work shift schedules or did not work, and have a higher average body mass index.
For the study, sleep duration irregularity was defined as a standard deviation [SD] of more than 120 minutes. Those participants who had a greater degree of sleep irregularity were more likely to have high coronary artery calcium burden than those whose sleep duration was more more regular, defined as an SD of 60 minutes or less (> 300; prevalence ratio, 1.33 [95% CI, 1.03 – 1.71]), as well as abnormal ankle-brachial index (< 0.9, prevalence ratio, 1.75, [95% CI, 1.03 – 2.95]).
Further, those with irregular sleep timing (SD > 90 minutes) were more likely to have a high coronary artery calcium burden (prevalence ratio, 1.39 [95% CI, 1.07 – 1.82]) in comparison with those with more regular sleep timing (SD < 30 minutes).
“The biggest surprise to me was that 30% of the participants in the study had total sleep times that varied by more than 90 minutes over the course of the week,” Full said. “This is consistent with prior studies that suggest that a large proportion of the general public have irregular sleep patterns, not just shift workers.”
Investigating Next Steps
In additional analyses, Full and colleagues found that sleep duration regularity continued to be associated with high coronary artery calcium burden and abnormal ankle-brachial index when accounting for severe obstructive sleep apnea, average nightly sleep duration, and average sleep fragmentation.
Notably, when sleep duration was added, all participants with more irregular sleep durations (SD > 60 minutes) were more likely to have a high coronary artery calcium burden, as compared with those with regular sleep durations (SD < 60 minutes). The results remained when participants who reported shift work, including night shift work, were excluded.
Additional studies are needed to understand the mechanisms, the study authors write. Night-to-night variability in sleep duration and sleep timing can cause desynchronization in the sleep-wake timing and circadian disruption.
“A key issue highlighted in this study is that sleep irregularity itself, independent of how much sleep people were getting, was related to heart health. Sleep is a naturally recurring phenomenon, and maintaining regularity helps provide stability and predictability to the body,” Michael Grandner, PhD, associate professor of psychiatry and director of the Sleep and Health Research Program at the University of Arizona College of Medicine, told Medscape Medical News.
Grandner, who wasn’t involved with this study, has researched sleep irregularity and associations with cardiovascular disease, diabetes, obesity, and many other adverse outcomes.
“When people have very irregular sleep schedules, it may make it harder for the body to optimally make good use of the sleep it is getting, since it such a moving target,” he said. “The unique angle here is the ability to focus on regularity of sleep.”
The study was supported by the National Heart, Lung, and Blood Institute and the National Center for Advancing Translational Sciences of the National Institutes of Health. One author received grants and consulting fees from pharmaceutical companies unrelated to the research. The other authors and Grandner have disclosed no relevant financial relationships.