What Losing An Hour's Sleep
Really Does To Your Children
How many hours' sleep does your child get a night? However much
it is, it's likely to be less than you had as a child.
While many parents - thanks to baby gurus - obsess about babies'
sleep, this tails off after the nursery years.
The result is that modern children, from primary school age right
up to secondary, get on average an hour less sleep each night
than they did 30 years ago.
Research suggests that half of all pre-teens get less than seven
hours' sleep on weekday nights, and only slightly more than six
hours when they reach secondary school.
Why is this happening? The common 21st-century afflictions: over-scheduling
of activities, burdensome homework, lax bedtimes and TVs and mobile
phones in the bedroom.
Plus parental guilt: home from work late, wanting time with the
children, reluctant to play the tyrant by ordering them to bed.
Until now, we could ignore the lost hour - if we were even aware
it existed - because we did not know its true cost to children.
But using newly developed technological and statistical tools,
sleep scientists have been able to isolate and measure its impact.
Because children's brains are a work in progress until the age
of 21, and much of that work is done while asleep, this lost hour
appears to have an impact on children it simply doesn't have on
The surprise is not merely that sleep matters - but how much
it matters. Not just to academic performance and emotional stability,
but to seemingly unrelated phenomena, such as the obesity epidemic
and the rise of attention deficit disorder.
Some scientists claim sleep problems during formative years can
cause permanent changes in brain structure. It's even possible
that many of the hallmark characteristics of being a teenager
- moodiness, depression and binge drinking - are symptoms of chronic
A few years ago, Dr Avi Sadeh at Tel Aviv University sent 77
third and fifth year pupils home with instructions to go to bed
earlier or stay up later for three nights.
Each child was given an actigraph - a wristwatch-like device
that allowed researchers to see how much sleep they were getting.
The team found that the first group managed to get 30 minutes
more sleep a night. The other group got 31 minutes less.
After the third night, a researcher tested the children using
a computerised version of an IQ test.
Dr Sadeh discovered that a slightly sleepy fifth former performed
in class like a third-former - the loss of just one hour's sleep
is equivalent to the loss of two years of cognitive maturation
Dr Sadeh's findings are consistent with other researchers' work
- which point to the academic consequences of small sleep differences.
With the benefit of MRI scans, researchers are starting to understand
exactly how sleep loss impairs a child's brain.
Tired children can't remember what they just learned, for instance,
because their brain cells lose their 'plasticity', becoming incapable
of forming new connections necessary to encode a memory.
A different mechanism causes children to be inattentive in class.
Sleep loss debilitates the body's ability to extract glucose from
Without this, one part of the brain suffers more than the rest
- the prefrontal cortex, which is responsible for what's known
as Executive Function - orchestrating your thoughts to fulfil
a goal and perceiving the consequences of your actions.
A tired brain gets stuck on a wrong answer and can't come up
with a more creative solution, repeatedly returning to the answer
it already knows is wrong.
Both these mechanisms weaken a child's capacity to learn during
the day. But the most exciting science concerns what the brain
is up to when a child is asleep.
Dr Matthew Walker, an academic from California, explains that
during sleep the brain shifts what it learned that day to more
efficient storage regions of the brain. Each stage of sleep plays
its own unique role in capturing memories.
For example, studying a foreign language requires learning vocabulary,
remembering new sounds and motor skills to enunciate the new word.
The vocabulary is processed by one area of the brain early in
the night during slow-wave sleep, a deep slumber without dreams.
Meanwhile, memories that are emotionally laden get processed
during REM, or dreaming sleep.
Children's sleep is different in terms of its quality from adult
sleep because they spend more than 40 per cent of it in slowwave
stage (adults spend just
This is why a good night's sleep is so important to children
for long-term learning.
But perhaps most fascinating is the way emotions associated with
a memory affect where it gets processed.
Negative memories get processed by one area of the brain, the
amygdala; positive or neutral memories get processed by another,
Sleep deprivation hits the hippocampus harder than the amygdala.
The result is that sleep-deprived people fail to recall pleasant
memories, yet remember gloomy memories very well.
And what of the hidden role sleep plays in the obesity epidemic?
In the past three decades, childhood obesity has tripled. For
a long time, we all focused on one culprit - television.
The connection to obesity seemed so obvious that few people thought
it even needed to be supported scientifically.
But here's the fascinating thing: researcher Elizabeth Vandewater
at the University of Texas found that obese children watch no
more TV than thin children.
In fact, while obesity has increased exponentially since the
Seventies, children watch only seven more minutes of TV a day.
While they do average a half-hour of video games and internet
surfing on top of television viewing, the leap in obesity began
in 1980, before home video games and the invention of the web.
So something other than television is making children fatter.
Five years ago, already aware of an association between sleep
apnoea and diabetes, Dr Eve Van Cauter, a sleep researcher, discovered
a ' neuroendocrine cascade' that links sleep to obesity.
Sleep loss increases the hormone ghrelin, which signals hunger,
and reduces leptin, which suppresses appetite. It also elevates
the stress hormone cortisol, which stimulates your body to make
Human growth hormone is also disrupted - normally secreted as
a single big pulse at the beginning of sleep, it is essential
for the breakdown of fat.
It's drilled into us that we need to be more active to lose weight.
So it confuses us to hear that a key to staying thin is to spend
more time doing the most sedentary inactivity humanly possible
- sleep. Yet this is what scientists are finding.
All the studies point the same way: children who sleep less are
fatter than those who sleep more.
How sleep impacts on hormones is an entirely different way of
explaining what makes people fat or thin - we normally think of
weight gain as a straightforward calories consumed/calories burned
equation. But even by that familiar formula, the relation of sleep
to weight makes sense.
While few calories are being burned in bed, at least a child
is not eating. In addition, children who don't sleep well are
often too tired to exercise. So the net calorie burn after a good
night's rest is higher.
Most of us have coped on too little sleep for years and managed
to get by. But given this new research, when it comes to our children's
developing brains, are we willing to take the risk?
February 23, 2010