Long sleeps linked with death and stroke
A new study has suggested adults who get more than eight hours of shut-eye a night are at risk of sleeping themselves into an early grave.
Long sleepers were 30 per cent more likely to die early than those who slept for six and eight, according to 10 years of research on sleeping habits and health.
And danger awaits short sleepers, too – 12 per cent more of them died compared to those in the six to eight group.
Middle-aged and older people who slept more than eight hours a night experienced a 45 per cent greater risk of stroke, according to a study.
University of Warwick professor Franco Cappuccio analysed 16 studies that surveyed a total of one million people around the world. He corrected for factors that may cause people to sleep for longer, such as depression or use of sedatives – but found the association with early death was still there.
A related study, recently published in the peer-reviewed journal Neurology, found middle-aged and older people who slept more than eight hours a night were also more susceptible to stroke – 45 per cent more likely, in fact. There was a 19 per cent increased risk of stroke for those who slept less than six hours.
These findings are seconded by Greg Jacobs from the University of Massachusetts, who says there is a wealth of evidence showing a U-shaped relationship between sleep duration and mortality – the further away from seven hours a night you are, the more likely to you are to die early.
"The research over the past 10 years suggests that sleeping eight hours a night may be a health risk," he told the BBC's More or Less radio programme. "Seven hours sleep keeps turning up over and over again."
Seven hours is also the median sleep duration for adults in many different parts and cultures of the world, Dr Jacobs said, which would appear to indicate it is the natural sweet spot.
BUT BEFORE YOU RESET YOUR ALARM - HEAR THIS
But the much-touted 'seven hours' is at the lower end of recently-revised United States guidelines, which recommend between seven and nine hours a night for adults aged between 18 and 64. As little as six or as many as 10 "may be appropriate", according to the US National Sleep Association – even as many as 11 hours for young adults aged 18 to 26.
There are a few important caveats when discussing sleep studies. The first is that they rely on participants' reported hours of sleep, which are notoriously unreliable. People have to rely on their memory and often find it hard to tell exactly how many hours they "slept" from how long they spent in bed, Professor Cappuccio said.
"It's very unusual to measure sleep very accurately. It has to be taken with a pinch of salt," he told the BBC.
Secondly, the study indicates a correlation between long sleep and early death, but not causation. Professor Cappuccio believes people who slept for longer were most likely affected by some otherwise pre-symptomatic health condition, for which the study could not control. Ergo, he says it is probably not the sleep itself causing health problems, but some other underlying issue.
Finally, these studies look at correlations in the broader population and should not be the basis of any individual decision-making, says Dorothy Bruck, sleep psychologist at the Sleep Health Foundation. People are better off following their own body's natural sleep patterns rather than the results of a large study, she says.
"Listen to what your body's telling you. While these things are interesting, they shouldn't change individual behaviour, because we've got no idea why these associations exist," she says.
Even the effect of chronic under-sleeping is up for debate. While numerous studies show an association with problematic alterations in metabolism, higher blood pressure and a greater risk of heart disease and diabetes, some scientists argue there are other factors involved and that sleep deprivation experiments place patients under too much stress to be reliable.
Jim Horne, a British sleep expert, has long been sceptical of rigid prescriptions around how much sleep people "need". Sleeping patterns had changed throughout history, humans were very adaptable and the notion of "sleep debt" was a largely modern invention, he told The Observer in 2006. "A lot of sleepiness is more imagined than real," he said.
People who habitually sleep five hours or less may be doing so due to other factors keeping them awake or stressing them out, Professor Horne told the BBC this year.
"Clearly it's not so much lack of sleep which is the problem, it's the fact that you are maybe having a stressed lifestyle," he said. Like Professor Bruck, he contends adults should generally sleep for the duration their body demands, rather than following prescriptions.
- Sydney Morning Herald