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. 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.

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.

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.

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

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.