Nurse checking the report

If you’re not getting enough sleep, you may be increasing your heart disease risk, according to new research in the American Heart Association journal Hypertension.

To determine the impact of circadian rhythm (about 24-hour) disturbances on cardiovascular function in sleep-deprived people, researchers studied 26 healthy people ages 20 to 39. The study participants were restricted to five hours of sleep for eight days (sleep restriction) with fixed bedtimes (circadian alignment) or bedtimes delayed by 8.5 hours on four of the eight days (circadian misalignment).

In the study, sleep restriction with delayed bedtimes was associated with:

  • Increased heart rate during the day for fixed bedtimes and delayed bedtimes groups and even more so at night when sleep restriction was combined with delayed bedtimes.
  • Reduced heart rate variability at night.
  • Increase in 24-hour urinary norepinephrine excretion in the sleep-restricted, delayed-bedtime group. (Norepinephrine is a stress hormone that can constrict blood vessels, raise blood pressure and expand the windpipe.)
  • Reduced vagal activity related to heart rate variability during deeper sleep phases (NREM), which have a restorative effect on cardiovascular function in normal individuals. The vagal nerve’s main effect is lowering the heart rate.

“In humans, as in all mammals, almost all physiological and behavioral processes, in particular the sleep-wake cycle, follow a circadian rhythm that is regulated by an internal clock located in the brain,” said Daniela Grimaldi, M.D., Ph.D., lead author and a research assistant professor at Northwestern University in Chicago. “When our sleep-wake and feeding cycles are not in tune with the rhythms dictated by our internal clock, circadian misalignment occurs.”

Researchers said insufficient sleep is particularly common in shift workers, who represent 15 percent to 30 percent of the workers in industrialized countries.

“Our results suggest shift workers, who are chronically exposed to circadian misalignment, might not fully benefit from the restorative cardiovascular effects of nighttime sleep following a shift-work rotation,” said Grimaldi, who also collaborates with the Sleep Metabolism and Health Center of the University of Chicago where the study was conducted.

“In modern society, social opportunity and work demand have caused people to become more active during late evening hours leading to a shift from the predominantly daytime lifestyle to a more nocturnal one. Exposure to consecutive days of sleep loss can impair cardiovascular function and these negative effects might be enhanced when changes in feeding and/or sleep-wake habits lead to a circadian disruption,” she said.

Since shift work often can’t be avoided, researchers encourage a healthy diet, regular exercise and more sleep.

Next, researchers want to see whether people exposed to sleep loss with or without circadian misalignment can recover once they get consecutive days of sleep extension.