Many of us try, but often fail, to get eight hours’
sleep each night. This is widely assumed to be the
ideal amount – but some experts now say it’s too
much, and may actually be unhealthy.
We all know that getting too little sleep is bad. You
feel tired, you may be irritable, and it can contribute
to obesity, high blood pressure, diabetes, and heart
disease, doctors say. But too much sleep? You don’t
often hear people complaining about it.
However, research carried out over the past 10 years
appears to show that adults who usually sleep for less
than six hours or more than eight, are at risk of
dying earlier than those sleep for between six and
eight hours.
To put it more scientifically, there is a gradual
increase in mortality risk for those who fall outside
the six-to-eight-hour band.
Prof Franco Cappuccio, professor of cardiovascular
medicine and epidemiology at the University of
Warwick, has analysed 16 studies, in which overall
more than a million people were asked about their
sleeping habits and then followed up over time.
Cappuccio put the people involved into three broad
groups:
• those who said they slept less than six hours a night
• those who said they slept for between six and eight
hours
• those who said they slept for more than eight hours
His analysis showed that 12% more of the short
sleepers had died when they were followed up,
compared to the medium sleepers.
However, 30% more of the long sleepers had died,
compared to the medium sleepers.
That’s a significant increase in mortality risk, roughly
equivalent to the risk of drinking several units of
alcohol per day, though less than the mortality risk
that comes from smoking.
But can it really be true that getting nine hours’
sleep is worse for you than getting five?
There are different ways of looking at this.
Cappuccio was aware of the possibility that people
sleeping too long might be depressed, or might be
using sleeping pills. He corrected for this, though,
and found the association was still there.
His own theory is that people who sleep for more
than eight hours sometimes have an underlying
health problem that is not yet showing in other
symptoms.
So, it’s not the long sleep that is causing the
increased mortality risk, it’s the hidden illness.
But not everyone agrees. Prof Shawn Youngstedt of
Arizona State University carried out a small study
involving 14 young adults, persuading them to spend
two hours more in bed per night for three weeks.
They reported back that they suffered from
“increases in depressed mood” as Youngstedt puts it,
and also “increases in inflammation” – specifically,
higher levels in the blood of a protein called IL-6,
which is connected with inflammation.
The participants in the study also complained about
soreness and back pain. This makes Youngstedt
wonder whether the problem with long sleep is the
prolonged inactivity that goes with it.
He has now been carrying out an experiment where
long-sleeping and average-sleeping adults are asked
to spend an hour less in bed each night. The results
will be published soon, he says.
Anyone studying sleep has to contend with a number
of difficulties. One is that it’s often not possible to
measure sleep very accurately.
“We tend to rely on very simple methods of asking
people on average how many hours they sleep a
night. It has to be taken with a pinch of salt,” says
Cappuccio.
“Naturally, you have to rely on your memory, and…
you don’t know if you’re reporting time in bed or
time asleep and whether you’re accounting for naps,
and so forth.”
Apparently we have a general tendency to
overestimate how long we’ve been asleep. And when
it comes to quality of sleep, all experts seem to agree
it could affect your health, but it’s even harder to
measure than how long you sleep.
Another caveat is that babies, children and teenagers
all have different sleep requirements than adults.
But if it’s the case that less than six hours of sleep is
too little for an adult, and more than eight hours is
too much, what is the ideal amount – what do our
bodies want?
As we’ve reported before, there is a lot of evidence to
suggest that until the late 17th Century people did not
sleep in one long uninterrupted stretch, but in two
segments, separated by a period of one or two hours
in which they prayed, read, chatted, had sex, smoked,
went to the toilet or even visited neighbours.
That may be more natural than the current tendency
to sleep – or try to – in one stretch.
Putting this question to one side, and focusing on the
total number of hours spent asleep, Cappuccio says
three-quarters of people in the Western world sleep
between six and eight hours a night on average, the
range associated with the best results in terms of
length of life.
But can we say that eight hours are better than six?
The magic number, according to Dr Gregg Jacobs, of
the Sleep Disorders Center at the University of
Massachusetts Medical School may actually be seven.
“Seven hours sleep keeps turning up over and over
again,” he says.
He points, for example, to the National Sleep
Foundation’s annual poll of a random sample of
adults in the US
“The typical adult today [in that poll] reports seven
hours of sleep. And that actually seems to be the
median sleep duration in the adult population around
the world. That suggests there’s something around
seven hours of sleep that’s kind of natural for the
brain.”
But if you enjoy sleeping, spend a lot of time in bed
and feel good, you’re probably just fine. There’s no
hard evidence that extra time asleep, or just lying
down and relaxing, is going to kill you.