Poor sleep is linked to an increased risk of dying from heart disease or stroke among people who have a cluster of interrelated risk factors known as metabolic syndrome, according to a study published Wednesday in the Journal of the American Heart Association.
Specifically, the study found that people with metabolic syndrome were twice as likely to die from heart disease and stroke than people without it — if they also failed to get more than six hours of sleep.
If they exceeded six hours of sleep, the risk was smaller.
“If you have several heart disease risk factors, taking care of your sleep and consulting with a clinician if you have insufficient sleep is important if you want to lower your risk of death from heart disease or stroke,” said Julio Fernandez-Mendoza, the study’s lead author and a sleep psychologist at Pennsylvania State University (Penn State), in a released statement.
A common combination
As background information in the study points out, about one-third of American adults have metabolic syndrome, a combination of various factors that increase an individual’s risk of heart disease, stroke and type 2 diabetes.
For the current study, those factors included — in addition to high blood pressure and high fasting blood sugar — a body mass index (BMI) higher than 30, elevated total cholesterol and high triglyceride levels. An individual had to have at least three of those five risk factors to be diagnosed with metabolic syndrome.
Some research has also suggested that not getting enough sleep may increase the negative health impact of metabolic syndrome, particularly on early death. But the reliability of those findings was limited by the way sleep duration was determined — through the self- reports of the studies’ participants. People’s perceptions of how much sleep they get are often unreliable.
The current study measured sleep duration more objectively. Fernandez-Mendoza and his colleagues randomly selected 1,344 adults (average age 49) from among a larger group of people who had agreed to spend a night in a sleep lab as part of the Penn State Adult Cohort, a study of sleep disorders. Almost 40 percent of them had metabolic syndrome.
The participants were followed for an average of 17 years. Over that period, 22 percent of them died. When the researchers compared how much sleep they had recorded in the lab with their likelihood of dying prematurely, they found a distinct correlation. People with metabolic syndrome who were not short sleepers — who had slept longer than six hours in the lab — were 1.49 times more likely to die of stroke than people without the syndrome. But people with metabolic syndrome who were short sleepers — who slept less than six hours — were 2.1 times more likely to die of either stroke or heart disease.
In fact, the short sleepers with metabolic syndrome were twice as likely as people without the syndrome to die from any cause.
The increased risk was associated with all five metabolic-syndrome factors, but it was greatest among people who had high blood pressure and/or high fasting blood sugar.
It also occurred even after the researchers adjusted for sleep apnea — a disorder marked by pauses in breathing during sleep — a known risk factor for heart disease.
Limitations and implications
The study comes with several important caveats. Most notably, it is an observational study, which means it can show only a correlation, not a direct causal link, between poor sleep and an increased risk of premature death among people with metabolic syndrome. Furthermore, sleep duration was based on a single night in a sleep lab.
Other limitations include the demographic makeup of the study’s participants: They all came from one region of the country (central Pennsylvania) and were predominantly white (88 percent).
Still, the study’s findings underscore the important role that sleep plays in health — a role that is often underappreciated. As the American Heart Association noted in a scientific statement released last fall, most Americans get too little sleep, despite mounting evidence that chronic short sleep and sleep disorders have an adverse impact on obesity, high blood pressure, type 2 diabetes and heart disease.
FMI: The current study can be read in full on the website for the Journal of the American Heart Association. For tips on how to get a good night’s sleep, go to the National Sleep Foundation’s website.