Clinical Context

Sleep has been increasingly recognized as an important element of overall wellness, and a systematic review by Laksono and colleagues described the relationship between abnormal sleep duration and the risk for cardiovascular disease (CVD). The authors of this study combined evidence from 10 trials with a total of more than 360,000 adults, and their results were published in the February 7, 2022 issue of Sleep Disorders.^[1]

In 9 of the 10 included studies, sleep duration had a significant effect on cardiovascular (CV) outcomes. Short sleep duration was significantly associated with higher risks for hypertension, coronary heart disease, and a combined outcome of atrial fibrillation, myocardial infarction, and stroke. Long sleep duration was associated with higher risks for atrial fibrillation and coronary heart disease.

Although this research corroborates other studies linking abnormal sleep to worse CV outcomes, there has been little research focused on the relationship between sleep and atherosclerotic disease itself. The current study by Full and colleagues addresses this issue.

Study Synopsis and Perspective

Irregular sleep -- such as inconsistent sleep duration or sleep timing -- may increase the risk of developing atherosclerosis among adults older than age 45 years, 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 [CV] 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, Nashville, Tennessee, 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 February 21 in the Journal of the American Heart Association.^[2]

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 6 US communities who completed 7-day wrist actigraphy assessment and kept a sleep diary between 2010 and 2013.

For subclinical markers of CVD, participants underwent assessments of coronary artery calcium (CAC), carotid plaque presence, carotid intima-media thickness, and ankle-brachial index (ABI).

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 CVD risk factors and sleep characteristics, such as obstructive sleep apnea (OSA), sleep duration, and sleep fragmentation.

The mean age of the participants was 68.6 ± 9.2 years, and 53.6% were women. About 37.9% identified as White, 27.6% as Black, 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. Participants 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 (BMI).

For the study, sleep duration irregularity was defined as a sleep deviation [SD] of more than 120 minutes. Those participants who had a greater degree of sleep irregularity were more likely to have high CAC burden than participants whose sleep duration was more regular, defined as an SD of 60 minutes or less (> 300; prevalence ratio [PR] 1.33 [95% CI: 1.03, 1.71]), as well as abnormal ABI (< 0.9; PR 1.75 [95% CI: 1.03, 2.95]).

Further, participants with irregular sleep timing (SD > 90 minutes) were more likely to have a high CAC burden (PR 1.39 [95% CI: 1.07, 1.82]) in comparison with participants 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."

In additional analyses, Full and colleagues found that sleep duration regularity continued to be associated with high CAC burden and abnormal ABI when accounting for severe OSA, 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 CAC burden as compared with participants 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 wrote. 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, Tucson, Arizona, told Medscape Medical News.

Grandner, who was not involved with this study, has researched sleep irregularity and associations with CVD, 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.

Clinical Implications

• A previous systematic review by Laksono and colleagues found that short sleep duration was significantly associated with higher risks for hypertension, coronary heart disease, and a combined outcome of atrial fibrillation, myocardial infarction, and stroke. Long sleep duration was associated with higher risks for atrial fibrillation and coronary heart disease.
• In the current study by Full and colleagues, variability of sleep duration was associated with higher CAC score, more carotid plaque, and abnormal ABI. Variability of sleep timing was associated only with a higher CAC score.
• Implications for the healthcare team: The healthcare team should emphasize regular sleep, particularly in terms of sleep duration, to maximize CV health.

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