People who suffer from a lack of sleep and disordered sleep cycles could be increasing their chances of developing cardiovascular disease, according to a study in the American Heart Association’s Journal Hypertension.
The research carried out by scientists at Northwestern University in Chicago and the Sleep Metabolism and Health Center of the University of Chicago indicates that the hearts of shift workers and other people whose sleep patterns regularly vary from traditional hours of sleep may not refresh properly and that their involuntary bodily processes may malfunction.
This may help to explain observed increased cardiovascular risks detected in shift workers who account for 15 to 30 per cent of the working population in industrial countries. The researchers recommend that to counter this imbalance, shift workers should focus on a healthy diet, regular exercise and gaining more sleep.
Lack of sleep and disturbances of the circadian rhythm, the 24-hour cycle biological clock of humans, have been linked to the cardiovascular issues but the exact connection has not previously been determined. Good quality sleep is believed to be important in mental and physical health for humans.
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.”
Daniela Grimaldi, M.D., PhD, lead author and a research assistant professor from Northwestern University.
Grimaldi went on to say: “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.”
For the study, scientists recruited 26 healthy people aged between 20 and 39 years to investigate the impact of circadian misalignment. The participants were only allowed to sleep for five hours each day for eight days. The recommended daily amount of hours of sleep for adults is around seven to eight hours. Some of the people in the study had fixed sleep times that fit into normal circadian rhythms while other participants had circadian misaligned sleep patterns where their bedtimes were postponed by 8.5 hours for four of the eight days.
“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 Grimaldi. “When our sleep-wake and feeding cycles are not in tune with the rhythms dictated by our internal clock, circadian misalignment occurs.”
The study, supported by the National Institutes of Health, found that the participants with delayed bedtimes combined with sleep restrictions presented with:
- A raised heart rate for groups with fixed and delayed bedtimes with a greater increase for the group with sleep restriction combined with delayed bedtimes
- Less varied heart rates during the night
- An increase in excretion of the stress hormone norepinephrine in urine over 24 hours. Norepinephrine helps to narrow blood vessels, increase blood pressure and expand the windpipe
- Decrease in activity for the vagal nerve which helps to control the heart rate variability. It was especially lower during deep sleep, the period when the body is involved in restoring heart function
The study was carried out under lab conditions at the Sleep Metabolism and Health Center of the University of Chicago and further research would need to be carried out to determine whether the outcomes are replicated in a non-laboratory environment.
The researchers are hoping to investigate the impact of lack of sleep without changes in the circadian rhythm to observe how the body recovers.