Lack of sleep and circadian rhythm disturbances have been linked to increased risk of heart diseases, but the cause is unclear. Researchers from Northern University in the US conducted a study to determine the impact of circadian rhythm disturbances on cardiovascular function in sleep deprived people.
The researchers studied 26 healthy people between the ages of 20 to 39. The study participants were restricted to five hours of sleep for eight days (sleep restriction) with either fixed bedtimes (circadian alignment) or bedtimes delayed by 8.5 hours on four of the eight days (circadian misalignment).
‘Shift workers should focus on getting at least 8 hours of sleep to improve both mental and physical health.’
The study showed that sleep restriction combined with delayed bedtimes when compared to sleep restriction without delayed bedtimes was associated with an increased heart rate during the day for both fixed bedtimes and delayed bedtimes groups. It was even more so at night when sleep restriction was combined with delayed bedtimes.
The researchers said that the participants experienced reduced heart rate variability at night; an increase in 24-hour urinary norepinephrine excretion in the sleep-restricted and delayed bedtimes group; and reduced vagal activity related to heart rate variability during deeper sleep phases (NREM). In normal individuals, the deeper sleep phases have a restorative effect on cardiovascular function.
Norepinephrine is a stress hormone that can constrict the blood vessels, elevate blood pressure and expand the windpipe. The vagal nerve lowers the heart rate, said researchers.
"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 from Northwestern University.
"When our sleep-wake and feeding cycles are not in tune with the rhythms dictated by our internal clock, circadian misalignment occurs," said Grimaldi.
Sleep deprivation is common among shift workers, who represent 15 to 30% of the working population in industrialized companies.
"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.
The study is published in the journal Hypertension.