Varied Nightly Bedtime, Sleep Duration Linked to CVD Risk

Patrice Wendling

March 02, 2020

People who frequently alter the amount of sleep and time they go to bed each night are twofold more likely to develop cardiovascular disease, independent of traditional CVD risk factors, new research suggests.

Prior studies have focused on shift workers because night shift work will influence circadian rhythm and increase CVD risk. But it is increasingly recognized that circadian disruption may occur outside of shift work and accumulate over time, particularly given modern lifestyle factors such as increased use of mobile devices and television at night, said study coauthor Tianyi Huang, ScD, MSc, of Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts.

"Even if they tend to go to sleep at certain times, by following that lifestyle or behavior, it can interfere with their planned sleep timing," he said.

"One thing that surprised me in this sample is that about one third of participants have irregular sleep patterns that can put them at increased risk of cardiovascular disease. So I think the prevalence is higher than expected," Huang added.

As reported today in the Journal of the American College of Cardiology, the investigators used data from 7-day wrist actigraphy, 1 night of at-home polysomnography, and sleep questionnaires to assess sleep duration and sleep-onset timing among 1,992 Multi-Ethnic Study of Atherosclerosis (MESA) participants, aged 45 to 84 years, who were free of CVD and prospectively followed for a median of 4.9 years.

A total of 786 patients (39.5%) had sleep duration standard deviation (SD) > 90 minutes and 510 (25.6%) had sleep-onset timing SD > 90 minutes.

During follow-up, there were 111 incident CVD events, including myocardial infarction, coronary heart disease death, stroke, and other coronary events.

Compared with people who had less than 1 hour of variation in sleep duration, the risk for incident CVD was 9% higher for people whose sleep duration varied 61 to 90 minutes (hazard ratio [HR], 1.09; 95% confidence interval [CI], 0.62 - 1.92), even after controlling for a variety of cardiovascular and sleep-related risk factors such as body mass index, systolic blood pressure, smoking status, total cholesterol, average sleep duration, insomnia symptoms, and sleep apnea.

Moreover, the adjusted CVD risk was substantially increased with 91 to 120 minutes of variation (HR, 1.59; 95% CI, 0.91 - 2.76) and more than 120 minutes of variation in sleep duration (HR, 2.14; 95% CI, 1.24 - 3.68).

Every 1-hour increase in sleep duration SD was associated with 36% higher CVD risk (95% CI; 1.07 - 1.73).

Compared with people with no more than a half hour of variation in nightly bedtimes, the adjusted hazard ratios for CVD were 1.16 (95% CI, 0.64 - 2.13), 1.52 (95% CI, 0.81 - 2.88), and 2.11 (95% CI, 1.13 - 3.91) when bedtimes varied by 31 to 60 minutes, 61 to 90 minutes, and more than 90 minutes.

For every 1-hour increase in sleep-onset timing SD, the risk of CVD was 18% higher (95% CI; 1.06 - 1.31).

"The results are similar for the regularity of sleep timing and the regularity of sleep duration, which means that both can contribute to circadian disruption and then lead to development of cardiovascular disease," Huang said.

This is an important article and signals how sleep is an important marker and possibly a mediator of cardiovascular risk, said Harlan Krumholz, MD, of Yale School of Medicine in New Haven, Connecticut, who was not involved with the study.

"What I like about this is it's a nice longitudinal, epidemiologic study with not just self-report, but sensor-detected sleep, that has been correlated with well-curated and adjudicated outcomes to give us a strong sense of this association," he told | Medscape Cardiology. "And also, that it goes beyond just the duration — they combine the duration and timing in order to give a fuller picture of sleep."

Nevertheless, Krumholz said researchers are only at the beginning of being able to quantify the various dimensions of sleep and the degree to which sleep is a reflection of underlying physiologic issues, or whether patients are having erratic sleep patterns that are having a toxic effect on their overall health.

Questions also remain about the mechanism behind the association, whether the increased risk is universal or more harmful for some people, and the best way to measure factors during sleep that can most comprehensively and precisely predict risk.

"As we get more information flowing in from sensors, I think we will begin to develop more sophisticated approaches toward understanding risk, and it will be accompanied by other studies that will help us understand whether, again, this is a reflection of other processes that we should be paying attention to or whether it is a cause of disease and risk," Krumholz said.

Subgroup analyses suggested positive associations between irregular sleep and CVD in African Americans, Hispanics, and Chinese Americans but not in whites. This could be because sleep irregularity, both timing and duration, was substantially higher in minorities, especially African Americans, but may also be as a result of chance because the study sample is relatively small, Huang explained.

The authors note that the overall findings are biologically plausible because of their previous work linking sleep irregularity with metabolic risk factors that predispose to atherosclerosis, such as obesity, diabetes, and hypertension. Participants with irregular sleep tended to have worse baseline cardiometabolic profiles, but this only explained a small portion of the associations between sleep irregularity and CVD, they note.

Other possible explanations include circadian clock genes, such as clock, per2 and bmal1, which have been shown experimentally to control a broad range of cardiovascular functions, from blood pressure and endothelial functions to vascular thrombosis and cardiac remodeling.

Irregular sleep may also influence the rhythms of the autonomic nervous system, and behavioral rhythms with regard to timing and/or amount of eating or exercise.

Further research is needed to understand the mechanisms driving the associations, the impact of sleep irregularity on individual CVD outcomes, and to determine whether a 7-day SD of more than 90 minutes for either sleep duration or sleep-onset timing can be used clinically as a threshold target for promoting cardiometabolically healthy sleep, Huang said.

"When providers communicate with their patients regarding strategies for CVD prevention, usually they focus on healthy diet and physical activity; and even when they talk about sleep, they talk about whether they have good sleep quality or sufficient sleep," he said. "But one thing they should provide is advice regarding sleep regularity and [they should] recommend their patients follow a regular sleep pattern for the purpose of cardiovascular prevention."

In a related editorial, Olaf Oldenburg, MD, Luderus-Kliniken Münster, Clemenshospital, Münster, Germany, and Jens Spiesshoefer, MD, Institute of Life Sciences, Scuola Superiore Sant'Anna, Pisa, Italy, write that the observed independent association between sleep irregularity and CVD "is a particularly striking finding given that impaired circadian rhythm is likely to be much more prevalent than the extreme example of shift work."

They call on researchers to utilize big data to facilitate understanding of the association and say it is essential to test whether experimental data support the hypothesis that altered circadian rhythms would translate into unfavorable changes in 24-hour sympathovagal and neurohormonal balance, and ultimately CVD.

The present study "will, and should, stimulate much needed additional research on the association between sleep and CVD that may offer novel approaches to help improve the prognosis and daily symptom burden of patients with CVD, and might make sleep itself a therapeutic target in CVD," the editorialists conclude.

This research was supported by contracts from the National Heart, Lung, and Blood Institute (NHLBI), and by grants from the National Center for Advancing Translational Sciences. The MESA Sleep Study was supported by an NHLBI grant. Huang was supported by a career development grant from the National Institutes of Health.

Krumholz and Oldenburg have disclosed no relevant financial relationships. Spiesshoefer is supported by grants from the Else-Kröner-Fresenius Stiftung, the Innovative Medical Research program at the University of Münster, and Deutsche Herzstiftung; and by young investigator research support from Scuola Superiore Sant'Anna Pisa. He also has received travel grants and lecture honoraria from Boehringer Ingelheim and Chiesi.

J Am Coll Cardiol. Published online March 2, 2020. Abstract, Editorial

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