People who toss and turn at night are twice as likely to suffer a heart attack, a major study suggests.
Scientists said fragmented sleep should be considered an early warning sign of future health problems.
A study of nearly 13,000 people found that people who woke up repeatedly in the night were 99 per cent more likely to suffer from ischaemic heart disease – the medical term for a heart attack or severe angina.
People who took more than half an hour to fall asleep had a 52 per cent increased heart attack risk and 48 per cent increased risk of a stroke.
And those who got less than six hours of sleep a night were 24 per cent more likely to have a heart attack.
Japanese scientists said fragmented sleep should be considered an early warning sign of future health problems
Experts are not sure whether poor sleep actually causes heart problems, or whether people who are ill and already suffering symptoms are simply getting worse sleep.
But either way they warn that having a restless night should be considered a red flag for more serious concerns.
Study leader Dr Nobuo Sasaki, of Hiroshima University in Japan, said: ‘Poor sleep in patients with ischaemic heart disease may be characterised by shorter sleep and brief moments of waking up.’
Why does the link exist?
His study only looked at statistical trends, rather than the reasons behind the link between sleep and heart problems.
But Dr Sasaki, who yesterday presented his findings at the European Society of Cardiology congress in Barcelona, suspects poor sleep disrupts the way the body runs its core functions – pulse, breathing and blood pressure.
This combined system is called the ‘sympathetic nervous system’, which operates without us having to consciously think about it.
The system is run by a part of the brain called the adrenocortical axis, which is highly sensitive to hormone imbalances and fluctuations in stress.
Poor sleep may raise blood pressure
Dr Sasaki thinks poor sleep – particularly the stress of waking up at night – may have an impact on this sensitive part of the brain, which in turn could raise heart rate and blood pressure, increasing strain on the heart.
Dr Sasaki concluded: ‘Our results support the hypothesis that sleep deterioration may lead to cardiovascular disease. Poor sleep in patients with ischaemic heart disease may be characterised by shorter sleep and brief moments of waking up.’
He added: ‘Difficulty maintaining sleep reflects an increase in sleep fragmentation, which refers to brief moments of waking up and causes overactivity of the sympathetic nervous system and adrenocortical axis.’
What have other studies found?
Previous research, published by the University of California San Francisco last year, suggests people who do not sleep all the way through the night are at a 29 per cent increased risk of developing an irregular heartbeat.
Sleep problems have also been linked to increased risk of cancer, obesity, diabetes and Parkinson’s.
Experts believe this is because the brain needs time to ‘reset’ and ‘recalibrate’ each night, which is why we spend nearly third of our lifetimes sleeping.
If this doesn’t happen it can have a detrimental impact on crucial bodily systems, and our health suffers as a result.
Less sleep than ever before
Yet a large study published in 2014 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.’