Adults over age 45 who sleep an inconsistent number of hours a night and fall asleep at different times may be at higher risk of developing atherosclerosis, according to new research published in the Journal of the American Heart Association.
The study, which included a racially and ethnically diverse sample of over 2,000 adults with an average age of 69, found that those with irregular sleep habits were more likely to develop the disease, characterized by the buildup of plaque on the artery walls, than people with more consistent sleep habits.
“This study is one of the first investigations to provide evidence of a connection between irregular sleep duration and irregular sleep timing and atherosclerosis,” says Kelsie Full, PhD, MPH, study lead author and assistant professor of medicine in the division of epidemiology at Vanderbilt University Medical Center, in a press release.
Between 2010 and 2013, the participants wore a wrist device that detected when they were asleep and awake, and they completed a sleep diary for seven consecutive days. In addition, participants completed a one-night, in-home sleep study to measure sleep disorders involving breathing, sleep stages, waking after sleep onset, and heart rate. Sleep duration was defined as the total amount of time spent in bed fully asleep, while sleep timing was described as the time a person falls asleep each night.
The greatest irregularity in the number of hours participants slept was a variation of over two hours within one week. Those with the greatest irregularity in sleep timing varied the time they fell asleep by over 90 minutes within one week.
Researchers gauged the presence of plaque in the arteries by measuring calcified fatty plaque buildup in arteries (coronary artery calcium); fatty plaque buildup in neck arteries (carotid plaque presence); thickness of the inner two layers of the neck arteries (carotid intima-media thickness); and narrowed peripheral arteries (the ankle brachial index).
Data evaluated also included information from participant health records and questionnaires, such as age, sex, race and ethnicity, education, yearly income, work schedule, smoking status, alcohol consumption, physical activity, body mass index, blood pressure, and sleep habits.
The analysis found:
- Participants with irregular sleep durations that varied by over two hours within a week were 1.4 times more likely to have high coronary artery calcium scores compared to those with more consistent sleep durations within a week. The score measures the amount of calcified plaque in the arteries, which is the main underlying cause of cardiovascular disease events such as heart attacks and strokes.
- Participants with irregular sleep durations that varied by over two hours within a week were 1.12 times more likely to have carotid plaque and nearly twice as likely to have abnormal results from an ankle brachial index, a test of systemic atherosclerosis and stiffness in the blood vessels, comparing blood pressure at the ankle to blood pressure in the arm.
- No associations were found between sleep duration irregularity and abnormal carotid intima-media thickness.
- Participants with more irregular sleep timing, varying over 90 minutes within a week, were 1.43 times more likely to have high coronary artery calcium scores compared to those with more regular sleep timing, varying 30 minutes or less within a week.
- There was little evidence linking sleep timing irregularity with other cardiovascular disease markers.
“Maintaining regular sleep schedules and decreasing variability in sleep is an easily adjustable lifestyle behavior that can not only help improve sleep but also help reduce cardiovascular risk for aging adults,” says Full in the press release.
The cross-sectional nature of the study—the fact that sleep and atherosclerosis were measured at the same time—represents a limitation of the analysis because researchers were not able to assess if greater sleep irregularity causes the development of atherosclerosis. The results, however, are novel and support continued research to better understand sleep irregularity and the development of cardiovascular disease risk, according to the authors.
Photo caption: Atherosclerosis blockage forming
Photo credit: American Heart Association