MICHAEL worries that we鈥檙e not getting enough. Jim thinks some of us are
getting too much. Diane, on the other hand, suspects some people are not doing
it at quite the right time of day.
The issue is sleep, how much of it we really need each day and when we should
take it. And these views hail not from idle chatterers in a bar but from leading
experts Michael Bonnet, Jim Horne and Diane Boivin, who鈥檝e spent years studying
how people and their bodies respond to different sleep regimes.
Each of their views comes complete with statistics and lab data in tow,
underscoring the fact that there are no simple, one-line answers to the question
of what makes a good night鈥檚 sleep. But then, the science wouldn鈥檛 trigger such
passionate debate if there were. And passions certainly run high. Especially
over that most basic sleep question of all: how much is enough?
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Michael Bonnet runs a sleep lab at Wright State University, near Dayton,
Ohio. Based on data from his own and other researchers鈥� labs, Bonnet says young
adults need 8.5 hours of sleep a night. And while older adults may need slightly
less (detailed studies haven鈥檛 been done), few experts recommend less than 7.5
hours. That would mean many of us aren鈥檛 getting enough: surveys in
industrialised countries typically show that about two-thirds of people sleep no
more than 7 hours a night.
Bonnet belongs to a camp of increasingly vocal researchers, based mainly in
the US, who believe we鈥檙e in serious danger of becoming chronically sleep
deprived thanks to our workaholic culture. Indeed, he argues, we are already
paying a heavy price for marginalising sleep. In the early 1990s, the US
National Commission on Sleep Research reported in the 1990s, it estimated that
accidents caused by tiredness cost the US a staggering $56 billion a year
in hospital bills, property damage, insurance and other costs. And in Britain
about a quarter of motorway accidents involve drivers falling asleep at the
wheel.
So you鈥檇 think Jim Horne, director of Loughborough University鈥檚 sleep lab,
and Britain鈥檚 leading expert on sleep, would also be busy trying to persuade
people to sleep more. Not so. In fact, Horne believes we could even sleep less
without damaging our health. He is is one of the leading members of a second
camp which holds that the problem of mass sleep starvation is more imaginary
than real.
If more of us are dozing at the wheel, that鈥檚 because more of us are using
motorways, and driving on motorways is very dull. And there鈥檚 no good evidence,
says Horne, that people sleep any less now than they did, say, a century
ago.
Two more polarised views it鈥檚 hard to imagine. So where鈥檚 the science? How do
researchers go about determining what counts as too little, or too much,
sleep?
One approach is the Multiple Sleep Latency Test. The rationale here is that
the more sleep starved you are, the faster you fall asleep during the day. To
take the test, you lie in a darkened room for 20 minutes, or until your
brainwaves show you have entered light sleep鈥攚hichever happens soonest.
Your MSLT score is the average of four or five of these measurements in a single
day. Scores of 10 minutes or longer are apparently nothing to worry about. But,
according to the American Sleep Disorders Association, scores between 5 and 10
minutes indicate 鈥渕oderate鈥� sleep deprivation, and scores below 5 鈥渟evere鈥�
deprivation. Bonnet thinks increasing numbers of people are falling into these
latter categories because they are simply not sleeping enough at night. An extra
couple of hours at night can boost your MSLT score by up to five minutes,
greatly sharpening your reaction times in the process, he argues.
Others, however, have a problem with the MSLT scores. Some individuals, Horne
says, fall asleep very easily even when they show no other symptoms of daytime
sleepiness, such as poor concentration. Perhaps much of the variation seen in
MSLT scores simply means some people are naturally inclined to fall asleep
faster than others.
But MSLT scores aren鈥檛 the only source of evidence to support the 鈥渟leep
starvation鈥� argument. Think about alarm clocks. If we鈥檙e all getting a natural
amount of sleep, why do so many of us need these devices to wake up on time?
Nobody disputes the need is real. A study in 1993, for example, by Thomas
Wehr and his colleagues at the National Institute of Mental Health in Bethesda,
Maryland found that people who were used to sleeping for eight hours a night
before being woken by an alarm clock will sleep an extra two or three hours when
the clock is removed. At issue is how one interprets those extra hours of
snatched slumber.
To Bonnet and other likeminded researchers, they show just how desperate our
bodies are to catch up on lost slumber. But to Horne, those extra hours of sleep
reveal something different鈥攖hat at heart, most of us are sleep gluttons.
Just as we tend to overeat given half a chance, so too do we oversleep. Our
regular sleep 鈥渄iet鈥�, enforced by alarm clocks, may be necessary to stop us
becoming 鈥渟leep fat鈥�.
And sleep fat, like excess body fat, may be bad for you, says Horne鈥攁nd
he doesn鈥檛 just mean it can lead to fuzzy thinking and lethargy. In 1979, a
six-year follow-up study of a million respondents to a survey by the American
Cancer Society revealed something more worrying鈥攕ignificantly higher
mortality rates (from all causes) among those who slept longer than the average
seven to nine hours.
But such findings are deeply controversial. Bonnet is sceptical of the
American survey because the study used a health questionnaire that only touched
on sleep habits. So far, no one has tried to conduct a more detailed study to
find out for sure鈥攑robably because there are too many other factors
involved.
Behind all these arguments is an unspoken assumption that how much sleep
someone gets is the only thing that matters. But even that may not be true. Even
if you鈥檝e had enough sleep, you鈥檙e likely to be irritable or fed up if you wake
up at the wrong time, according to groundbreaking new research by Boivin and her
colleagues at the Brigham and Women鈥檚 Hospital in Boston, which is backed up by
similar findings from Simon Folkard of Swansea University and his colleagues at
the University of Manchester. This research has been widely hailed as the first
clear demonstration that our internal body clocks directly affect our moods.
Previously, researchers have tended to regard daily mood swings as the handiwork
of external circumstances only.
The longer most healthy people stay awake, the more irritable and fed up they
tend to become. Sleep tends to make us feel brighter. What Boivin and her
colleagues have discovered is that its effectiveness as a mood brightener
depends on the timing of your sleep in relation to your daily body clock.
Normally, there is a sharp dip in body temperature, for instance, around 5
am, and a longer-lasting peak in body temperature some 8 hours later. Wake up at
the dip in the cycle and you鈥檙e more likely to feel irritable鈥攅ven after a
good 8-hour stretch. Wake up at the peak, when body temperature is at its
highest, and you鈥檙e more likely to feel cheerful.
To experience the biggest overall lift in mood over the course of a day, you
need to time your 16 or so hours of wakefulness to centre around the peak in
body temperature that normally occurs between 2 pm and 4 pm鈥攚hich is
precisely what a normal pattern of sleep and wakefulness does. The reverse
approach鈥攃entring your hours of wakefulness on the daily dip in body
temperature鈥攚ould be a recipe for ill-temper, according to the new
studies.
These ideas aren鈥檛 new. Biologists have long suspected that the timing of
sleep influences how cheerful people feel when they are awake. But until now,
there hasn鈥檛 been a way to prove it. The chief obstacle has been discovering how
to tease apart the stress-inducing effects of simply being awake for long
periods and the underlying effects on mood of the body clock.
Boivin and her colleagues solved such problems by imposing a 30-hour-day
lifestyle on human guinea pigs living in an environment lacking natural light
and darkness cues. In such circumstances, the body clock, with its ups and downs
in temperature, continues to run over 24 hours. But subjects go to bed and wake
up in line with the longer cycle. As a result, they end up spending their waking
hours at a different phase of their body clock every day.
Horne agrees that quality, not quantity, is what鈥檚 important for sleep, but
timing, he says, may not be the only thing that affects sleep quality. Horne
draws a distinction between deep, or 鈥渟low-wave鈥�, sleep, which he believes is
biologically essential and lighter forms of sleep which are more optional.
Usually, slow-wave sleep dominates the first 6 hours, optional sleep the later
hours. But the balance shifts after long bouts of sleep deprivation. Experiments
in Horne鈥檚 own lab, for example, show that people who have been awake for 72
hours need just 8 hours of sleep to recover most of their usual powers of
concentration鈥攂ut, importantly, slow-wave sleep dominates those 8 hours.
Evidence, says Horne, that it is the type, rather than the amount, of sleep that
really matters.
Horne also reckons people adapt to less sleep by sleeping more efficiently.
You fall asleep quicker, spend less time in the lighter phases of the sleep
cycle and wake less during the night. Just as we can safely cut down on
calories, so there is a margin within which we can safely reduce time spent
asleep.
But if about a quarter of our sleep has no vital biological purpose, as Horne
suggests, why haven鈥檛 we evolved to sleep less? Maybe, says Horne, the extra
sleep helps us to conserve energy. Or maybe it鈥檚 a way of killing unproductive
time or of staving off the anxieties that go with being conscious.
Whatever the answer, Horne is convinced that the secret of a good night鈥檚
rest is to get about 6 hours of uninterrupted sleep. What鈥檚 more, he says, there
are hidden dangers in telling people they need a lot more than that. Those who
have managed on 6 hours a night for most of their lives will lie in bed worrying
about their inability to sleep longer.
And that, says Horne, is a recipe for insomnia.
