Increased mortality linked to longer sleeping times, study shows
Turns out sleeping in could kill you.
This is a surprise finding from a University of Sydney study that looked at lifestyle behaviours linked to an increased risk of death.
The other deadly sins are familiar: drinking too much, smoking, poor diet, inactivity and prolonged sitting. But researchers have found that sleeping more than nine hours a day can also increase the likelihood of meeting an early end.
Taken on its own, regular oversleeping meant a 44 per cent increased risk of death over the six-year study period. By contrast, sleeping fewer than seven hours a day meant a 9 per cent increased mortality risk.
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He said: "One of the possible explanations is 'reverse causality'. Long sleeping times could be indicative of an underlying, undiagnosed disease."
However, he says another explanation is more plausible. "In the survey, people were asked 'How long did you sleep?' This most likely elicits an answer to the question: 'How long were you in bed?'
"This says nothing about the quality of the sleep," Stamatakis said. "So, reported long sleep duration could in fact be indicative of fragmented, restless and poor-quality sleep."
And it is this, he says, which could be connected to increased mortality rates.
The study looked at more than 200,000 people aged 45 and older in New South Wales over a six-year period from 2006. It is one of the largest such studies undertaken, covering 11 per cent of the target population of NSW. It was published in PLOS Medicine on Tuesday.
The researchers found that a third of all deaths in this period were caused by unhealthy behaviours tracked by the study.
Surprisingly, it found that when combined with healthy behaviours, high alcohol intake on its own was the least risky single activity, with just an 8 per cent increased mortality.
"We have to be very, very careful about this one," Stamatakis said. "The cohort of this study [over 45s] has relatively low alcohol consumption.
"General population studies show exactly the opposite result. These show that harmful effects from alcohol start from moderate consumption levels."
Stamatakis said this study is definitely not a "licence to drink".
The researchers said what it does establish is "prolonged sitting and unhealthy sleep duration as two additional risk factors for all-cause mortality".
The study calculated mortality risk over the study period from each factor on its own, or a variety of combinations of the six health sins.
The study found that "combinations involving physical inactivity, sedentary behaviour and/or long sleep duration and combinations involving smoking and high alcohol consumption were most strongly associated with all-cause mortality."
People who engaged in all six risky behaviours were more than five times more likely to die during the study than the reference group of those who didn't smoke, ate well, exercised, drank moderately, slept well and kept active.
Stamatakis said the study did not take into account what is known as "social desirability bias". This is where respondents to questionnaires over-report positive social behaviours, such as eating fruit, and under-report socially negative behaviours, such as alcohol consumption.