A small new study published in the journal Hypertension finds that shortened sleep is connected to some negative markers, especially when it occurs outside of typical nighttime hours.
Of all the reasons to get a good night's sleep, protecting your heart might not be top of mind. But maybe it should be. Sleep duration has decreased 1.5 to 2 hours per night per person in the last 50 years. But several recent studies show links between shortened sleep duration, defined as less than six hours of sleep, and increased risk of cardiovascular disease—regardless of age, weight, smoking and exercise habits.
It's not completely clear why less sleep is detrimental to heart health, but researchers understand that sleeping too little causes disruptions in underlying health conditions and biological processes like glucose metabolism, blood pressure, and inflammation.
Among those studies, a 2011 European Heart Journal review of 15 medical studies involving almost 475,000 people, found that short sleepers had a 48% increased risk of developing or dying from coronary heart disease in a seven to 25-year follow-up period and a 15% greater risk of developing or dying from stroke during this same time.
Also, one 2008 study from the University of Chicago found a link between shortened sleep and increased coronary artery calcification (calcium deposits), "a good predictor of subsequent coronary artery disease," says researcher Diane Lauderdale, PhD, professor of epidemiology at the university's Pritzker School of Medicine.
Now, a small new study published in the journal Hypertension finds that shortened sleep is connected to some negative markers, especially when it occurs outside of typical nighttime hours.
In the study, which was conducted at a University of Chicago sleep lab, 26 healthy young adults were assigned to a week of shortened sleep, with just five hours of shut-eye each night. Half of the people slept during normal nighttime hours, and half slept during the day—a schedule familiar to shift workers, who don’t keep typical 9-5 work hours. The researchers measured blood pressure and heart rate during the day, urinary levels of norepinephrine, a stress hormone that can raise blood pressure, and heart rate variability, the variation of beat-to-beat intervals used as an indicator for cardiovascular risk.
For everyone in the study, sleep restriction resulted in a higher heart rate during the day. The group that slept during the day saw even more changes; they had higher levels of urinary norepinephrine and less heart rate variability at night, when they were awake. “There is a general awareness that when heart rate variability is reduced, this is a marker for increased cardiovascular risk,” says lead study author Dr. Daniela Grimaldi, research assistant professor at Northwestern University Feinberg School of Medicine.
“In the meantime, the only thing we can suggest to people is a combination of eating healthy food, doing physical activity, trying to sleep as much as they can and minimizing all the other lifestyle conditions that can lead to cardiovascular risk as well,” Grimaldi says.