In particular, a variation in sleep duration of more than 2 hours per night in the same week was tied to the development of hardened arteries.
“Poor sleep is linked with several cardiovascular conditions, including heart disease, hypertension, and type 2 diabetes,” says study author Kelsie Full, PhD, assistant professor of medicine at Vanderbilt University Medical Center.
“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 says.
The findings were published in theJournal of the American Heart Association.
Atherosclerosis is the buildup of fatty deposits, known as plaque, on artery walls. This can lead to narrowed arteries and reduced blood flow and oxygen in the body. The plaque can also burst and create a blood clot that blocks the artery, which can lead to a heart attack or stroke.
Between 2010 to 2013, the people in the study wore a wrist device that detected when they were awake and asleep for 7 days in a row, and they completed a 7-day sleep diary. They also completed a one-night sleep study to measure sleep disorders that involve breathing, sleep stages, and heart rate.
The research team looked at sleep duration, or the total amount of time spent in bed fully asleep in a night, and sleep timing, which was defined as the time the person fell asleep each night. They measured the presence of plaque in the arteries by assessing for coronary artery calcium (or calcified plaque buildup in arteries), carotid plaque (or fatty plaque buildup in neck arteries), carotid intima-media thickness (or thickness of the inner two layers of the neck arteries), and the ankle-brachial index (or narrow peripheral arteries), all of which indicate the presence of atherosclerosis.
Across the 7-day period, about 38% of participants had a sleep duration change of more than 90 minutes, and 18% had 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, work shift schedules or not work, and have a higher average body mass index.
Participants who had greater sleep duration irregularity, varying by more than 2 hours in a week, were 1.4-times more likely to have high coronary artery calcium scores than those who had more regular sleep durations that varied by 60 minutes or less. They were also more likely to have carotid plaque and an abnormal ankle-brachial index.
Those who had irregular sleep timing (that varied by more than 90 minutes in a week) were also 1.43-times more likely to have high coronary artery calcium burden than those with more regular sleep timing (that varied by 30 minutes or less).
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.
“Sleep is a naturally recurring phenomenon, and maintaining regularity helps provide stability and predictability to the body,” says Michael Grandner, PhD, associate professor of psychiatry and director of the Sleep and Health Research Program at the University of Arizona College of Medicine.
“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.”
“Sleep health is more than just getting enough sleep,” he says. “It also means getting quality sleep, at the right time, regularly.”