Getting to sleep at the same time each night helps the heart recover from the day and reduces the risk of heart disease, researchers have found.
A stable bedtime routine helps the heart filter out stress hormones – so people with chaotic sleep patterns are at greater risk of heart problems.
The study may explain why people who work night shifts or travel between time zones are more likely to suffer from heart problems later in life.
Scientists found people who did not get enough sleep and stayed up too late at night had a raised pulse and increased levels of harmful stress hormones.
Experts believe getting enough sleep, at the same time each night, allows the heart to rejuvenate.
Doctors have long warned that a lack of regular sleep raises the risk of obesity, diabetes, heart disease and even cancer.
But until now they have not been sure exactly why this is.
The new research, conducted by Northwestern University, Chicago, suggests allowing the heart to properly rejuvenate is key.
The research team believe this is strongly tied to an internal mechanism called the circadian rhythm.
Nearly all living things have this circadian rhythm or body clock - which synchronises bodily functions to the 24-hour pattern of the Earth’s rotation.
In humans, the clock is regulated by the bodily senses, most importantly the way the eye perceives light and dark and the way skin feels temperature changes.
The mechanism rules our daily rhythms, including our sleep and waking patterns and metabolism. It also determines if we are a ‘morning’ person or an ‘evening’ person.
There is growing evidence that altering this rhythm - for example by working antisocial hours or regularly traveling between different time zones - places a strain on the body clock and creates long term health problems.
Study author Dr Daniela Grimaldi, said: ‘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.
‘Our results suggest shift workers, who are chronically exposed to circadian misalignment, might not fully benefit from the restorative cardiovascular effects of night-time sleep following a shift-work rotation.
‘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.’
Her team carried out a sleep deprivation experiment on 26 healthy people, aged 20 to 39.
The study participants were restricted to five hours of sleep for eight days, with their bedtimes delayed by 8.5 hours on four of the eight days.
Their findings, published in the journal Hypertension, found disrupting sleep patterns in this way led to an increased heart rate.
They also found an increase in a stress hormone called norepinephrine, which can constrict blood vessels, raise blood pressure and expand the windpipe.
When people enter deep sleep, their heart beat is allowed to slow down - a process controlled by the vagal nerve.
But the participants in the study did not enter this state, showing reduced vagal activity and higher variability of heart beat.
Dr Grimaldi said: ‘In humans, as in all mammals, almost all physiological and behavioural processes, in particular the sleep-wake cycle, follow a circadian rhythm that is regulated by an internal clock located in the brain.
‘When our sleep-wake and feeding cycles are not in tune with the rhythms dictated by our internal clock, circadian misalignment occurs.’
Insufficient sleep is particularly common in shift workers, who represent 15 per cent to 30 per cent of the working population in industrialised countries.
It follows a large British study published in 2014 that suggested people in the UK get two hours less sleep a night than they did 60 years ago.
The authors of that study, from Oxford, Cambridge, Harvard, Manchester and Surrey universities, warned that people have become ‘supremely arrogant’ by ignoring the importance of sleep.
Professor Russell Foster, a neuroscience at the University of Oxford, said at the time: ‘We are the supremely arrogant species; we feel we can abandon four billion years of evolution and ignore the fact that we have evolved under a light-dark cycle.
‘What we do as a species, perhaps uniquely, is override the clock. And long-term acting against the clock can lead to serious health problems.’
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