Getting too little sleep is a well known health hazard, raising the risk of a host of conditions, including obesity and heart disease.
But, now a team of scientists have warned getting too much sleep can also be bad for the heart.
Their findings reveal a fine line between a healthy night’s sleep and shut eye habits that could increase the risk of early death.
Anything less than four hours sleep is deemed detrimental to a person’s cardiovascular health.
A lack of sleep is known to be linked to stress responses that increase heart rate, blood pressure and the secretion of the hormone adrenaline – all risk facts for heart disease.
Yet, the new study, by experts in Norway and Taiwan, found those people who sleep for more than eight hours a night also faced a higher risk.
However, it is not yet known why spending more time between the sheets negatively impacts on the heart.
The study identified no increased risk with sleeping between four and six hours a night, or between six and eight hours.
Yet, researchers found the risk overall was greater for women than men.
Study author Dr Linn Beate Strand, of the Norwegian University of Science and Technology, said: ‘Our results show that enough, but not too much sleep, is important for a healthy lifestyle.’
Doctors asked 392,164 adults in Taiwan who came in for medical checkups between 1998 and 2011 how much they slept at night.
During a follow-up period, the scientists discovered that 711 of those patients died of cardiovascular disease.
The study found that the risk of heart disease increased 50 per cent for those who slept less than four hours a night, as compared to participants who slept between four and eight hours.
Those people who slept for shorter periods of time, had a less favorable risk factor for heart disease.
But even after adjusting for those factors, the risk was still found to be 36 per cent greater.
It is not known precisely why less sleep increases the heart disease risk.
However, less sleep is known to be associated with stress responses that increase heart rate, blood pressure and secretion of adrenaline.
All of those functions are known risk factors of cardiovascular disease.
Furthermore, sleep deprivation has been linked with the secretion of inflammatory responses.
Past studies also found that there is an association between short sleep duration, decreased insulin sensitivity, obesity and diabetes.
As for the effects of getting too much sleep, the scientists found that those who slept more than eight hours a night had a 53 per cent greater risk of dying from coronary heart disease.
After adjusting for other risk factors, the study found that the risk was still 28 per cent higher.
Dr Strand said: ‘We don’t know which mechanism can explain a direct causal link between long sleep duration and an increased risk of dying from coronary heart disease.’
The scientists noted that education and marital status were among the variables adjusted in the analysis.
The also adjusted their analyses for other risk factors, including age, sex, BMI, systollic blood pressure, blood glucose, blood lipids, smoking, alcohol use and more.
The increased heart disease risk for both short or long sleep duration primarily affected women.
Additionally, people over the age of 65 also had higher risks, the study found.
Dr Strand said: ‘Women are more prone to sleep problems than men, and previous studies have also shown that women who sleep a little or a lot may be at increased risk for cardiovascular disease.’
The study was published in the International Journal of Cardiology.