By Mandy Oaklander
Getting too little sleep has been shown to have bad effects on the heart, and many studies have linked it to hypertension. 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.
Blood pressure didn’t change in either group, which could have been a result of the short study duration. But 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.