Fragmented sleep is bad enough on its own. Whether it's noisy neighbors, a crying baby or the rumble of garbage trucks, being woken up in the middle of the night is no fun. Loss of sleep is more than a nuisance, however; it brings on inflammation. Now a look at middle-aged and older adults finds that the inflammation it causes seems to play a role in the stiffening and clogging of arteries.
Poor sleep has been linked to a host of ills, from heart disease to Alzheimer's. While there remains the chicken and egg question — which came first — it has become clear that sleep problems and many other health issues are often found together.
The focus here was on the buildup of plaque, sticky material that can eventually close off blood flow entirely, in the blood vessels of over 1,600 middle-aged and older people. This buildup is sometimes called atherosclerosis and often begins in early adulthood.
People with fragmented sleep tended to have more calcium in the walls of the heart's arteries, a sign that plaque is building up there.
Using information from the Multi-Ethnic Study of Atherosclerosis (MESA), an ongoing United States-based study, begun in the year 2000 and designed to look at developing heart and blood vessel disease before there are obvious signs and symptoms of it, Vallat and team found that people whose sleep was more fragmented tended to have a higher coronary artery calcification (CAC) score, a test that measures the amount of calcium in the walls of the heart's arteries, a sign that plaque is building up there.
They also showed an increase in two types of white blood cells, neutrophils and monocytes, an indication that inflammation was on the rise.
To isolate the effect of sleep quality on inflammation and plaque buildup, the study controlled for age, ethnicity, gender, body mass index, sleep disorders, blood pressure and high-risk behaviors such as smoking. Of course it's not possible to control for everything, but this served to increase the likelihood that poor sleep and the buildup of plaque influence each other and are not a spurious association.
Disrupted sleep was linked to higher concentrations of the monocytes and neutrophils that are known to be key players in atherosclerosis.
Interestingly, this linkage did not show up in peoples' own subjective accounts of sleep quality. It only appeared when sleep was measured using actigraphy (wrist monitors) for seven nights or polysomnography (one night). Polysomnography records people's brain waves, the oxygen level in their blood, heart rate and breathing, as well as eye and leg movements. In other words, people's own accounts of how much and how well they are sleeping may not reflect the true quality of their sleep.
People interested in tracking their sleep habits should use objective measures, such as actigraphy or polysomnography, the authors suggest, for the same reason people tracking their blood pressure need to have measurements taken using a blood pressure cuff.
This doesn't settle the question of whether fragmented sleep might be causing low-grade inflammation or if increased inflammation might be worsening people's sleep. It does show that they tend to happen together, and it does offer one more reason to pay attention to whether you're getting enough sleep.