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>> Professor Tim Olds: Three activities, sleep,
physical activity, screen time occupy 16 hours
of a child's day.
So if you take an average 10 year-old child they sleep
for about ten hours a day on average.
They spend about 2 hours in physical activity of one sort
or another and they spend
about 4 hours a day in front of a screen.
So what I'd like to do today is just briefly talk
about these three activities and for each time I'm going
to talk firstly about what the health consequences are
of these activities.
These are of interest to us
because we know there are strong associations
between how people use their time and health outcomes
and this is true of these three activities.
So I want to outline the health implications of having too much
or too little of these activities.
I'm going to talk about the type of kids who get a lot
or a little of these activities.
What type of kids spend a lot of time in front of screens?
What type of kids get a lot of physical activity?
Who gets enough sleep and who doesn't get enough sleep
and finally, I want to take you through historical perspective
to see what's happened to these activities
over the last 50 to 100 years.
Is it true that kids are sleeping more now
than they used to?
Is it true they're watching screens more now?
Do kids spend as much time in front of the radio as they do
in front of the television today?
Let's just start with the, I guess the most simple,
less controversial one physical activity.
We know that physical activity in both children
and adults is associated with a whole symphony, a whole gamut
of mental and physical health benefits.
Physical activity in kids is divided mainly
into three different parts,
locomotion which is mainly walking,
what we call active transport, sport, and play.
If we have a look at sport these are the most common sports
to Australia, so when you add up the average number of minutes
that kids spend in different sports around Australia boys
and girls average the most common one is soccer,
basketball, Aussie Rules, dancing, cricket
and there are a few others after that.
Tennis I think comes after netball.
When we have a look at locomotion almost all
of the time they spend moving around is walking.
There's a small slice of time spent cycling
and even smaller slice of time spent
in what we call new locomotions, which are things
like skateboarding and roller skating.
If you have a look at active play then play is divided
into what they do outdoors and what they do indoors
and you see most of the active play is done outdoors and less
of it is just mucking around or playing in the playground
at school that occupies the play side of things.
And finally, there's a small slice of activity
which doesn't fall into any of those categories
and it's mainly things such as chores, and the kind
of things they do at school which raises them
above that average sort of level but isn't sport or locomotion.
So that's what we mean by physical activity but what kind
of kids get different levels of physical activity?
The recommended amount, the recommended dose
of physical activity is 60 minutes for children each day.
So that children age 5 to 18,
it's recommended they get 60 minutes each day.
But how many kids meet those guidelines?
Well, it really depends on how you understand the guidelines.
If you mean they should get 60 minutes every day on all days
of the week there are only about 20 percent of kids get that.
If you mean they should get it on most days of the week,
4 or 5 days a week then about 50 percent,
46 percent of kids meet these guideline.
If you mean they should get 60 minutes on average,
so they could get 200 minutes one day then nothing the next
day then we find about 60 percent
of kids meet the guidelines, and the method which I use
which I think is the way it really should be done,
if you randomly choose a child
and randomly choose a day what's the probability they meet
the guidelines?
In that case about two-thirds of kids meet the guidelines.
So the bottom line is that by a sane interpretation
of the regulations most kids meet those guidelines.
Most kids are sufficiently active according
to what the government recommends.
I personally think those recommendations are too low.
I think it should be raised two hours a day
and there's a discussion about that now
but that's the situation as it stands.
We find that physical activity declines consistently with age
from age 9 through 16, and these data by the way,
come from the National Children's Nutrition
and Physical Activity Survey.
The red dots here are the data for boys,
the yellow dots are data for girls
and every study shows the boys are more active,
in terms of physical activity, than girls.
We'll see later on, by the way
that every study also shows the boys get more screen time
than girls.
So the boys are basically on or off.
They're either doing nothing, in front of a television
or a video game console, or they're being active.
Girls have a lot of the middle area
where they're moving around,
socialising with friends and so forth.
There's a marked difference
in the distribution activity amongst boys and girls.
So there are sex differences, there are age differences
in who gets physical activity.
There are also differences in relation to household income,
whether you come from a rich family or poor family.
But interestingly there aren't differences
in the overall levels of moderate
to vigorous physical activity,
of physical activity that kids get.
Whether they come from the wealthiest quarter of households
in Australia or from the poorest they all get
about the same number of total minutes of physical activity.
Where the differences arise when you look at different types
of physical activity and the big differentiator is sport.
This screen shows the average minutes per day of sport
that kids from different households get.
And the kids from the richest households get considerably
more sport.
It's about 13 minutes more sport each day, an hour-and-a-half
of sport each week than kids from the poorest households.
That's important from two levels.
Firstly, because sport is more intense than other types
of physical activity so the overall energy expenditure
of kids from wealthy households is greater
than the overall energy expenditure than kids
from poorer households but also sports are associated
with other benefits not entirely associated
with the energy content of the activity, for example,
sport involves a greater socialisation.
It involves progressive learning of skills
where they build on other skills.
So sport has benefits quite apart from the amount
of energy that's involved in in sports,
the major differentiator among socio-economic groups,
in terms of children's physical activity.
Another predictor of how much activity kids get is their
weight status.
So if you look at normal weight kids their total daily energy
expenditure here is about 2400.
It's a unit we call MET minutes it's roughly one kilocalorie.
So about 2400 kilocalories for the average 9
to 16 year-old child who is of normal weight but if we look
at kids who are obese they get about 154 MET minutes,
154 kilocalories less, about 6 to 7 percent less
than the average normal weight child, so where does
that difference come from?
What are the obese kids not getting
that the lean kids are getting?
Well, the answer is basically sport.
Most that is made up by differences in sport.
Some is made up by differences in active play
and there are small or negligible amounts
in active transport, other types of physical activity,
and energy applied in areas other than physical activity.
So there are differences between, not in total minutes
of physical activity but differences in the type
of physical activity the kids from different weight stages get
and the main difference is made up of by differences in sport.
Now if you have a look at the differences
in that lean kids devote to different types of activity.
If you have a look at boys,
anything above the line here means
that lean kids spend more time doing these things.
These kids, anything below the line these kids spend more time
than lean kids.
And you see the big differences here are in team sports,
in partner sports, cycling, and the only area
where these kids get more activity is just
in general mucking around.
We find a similar sort of pattern with girls except
that dance is also another area
where leaner kids get more activity.
So there are very specific differences in the types
of activity that different kids get.
Well, what about trends in physical activity?
What's been happening?
Are kids less active now than they have been in the past?
Well, the short answer is we don't really know.
We don't have good measures of that.
We've got some pictures, some snapshots, for example,
this screen shows the percentage of children
who use active transport to get to school.
So they walk to school or cycle to school or skate to school
or whatever and it shows data from the United States,
from Canada, from Australia and from New Zealand,
and from the UK and you can see across all
of these studies there's a consistent decline.
You can't compare one to the other
because they used different definitions
and different populations but the decline is consistent,
so fewer kids are using active transport to get to school.
Fewer kids are walking to school.
They have opted to get a ride with their mom or dad.
So that's one consistent snapshot we've got
but really we don't have good pictures
of how overall physical activity has changed.
But we do have other measures.
We've got measures, for example of how the fitness
of children has changed and we've got measures
of how their weight has changed and also data
on how their energy intake, their food intake has changed.
Now if their food intake has increased maybe this is due
to increase in food intake rather
than the increase in physical activity.
We'll have a look at that.
But this shows data on kids' aerobic performance.
These data collected by my former PhD.
Student, Grant Tomkinson and he collected data
on 50 million children from more than 50 countries
around the world, combined them and had a look at the patterns
and this is the pattern that you get.
So this shows the percentage, the performance as a percentage
of performance in 1980.
We just chose the date 1980 just arbitrarily,
but the pattern you see is very clear that performance increases
until 1970 then after 1970 it declines very, very rapidly.
It declines at the rate of about 3 to 4 percent per decade.
That means that your kids are likely to be about 10
to 15 percent less fit than you were when you were their age
and that their children, if this trend than continues,
will be 30 percent less fit than you were at that age.
There's a slight sign, this data goes up to about 2000,
some signs in recent years,
the last 5 years there may be a slight up trend in that
but there's been a rapid decline in the physical fitness
of children over that time, the aerobic fitness
of children over that time.
So Grant's work has definitively shown that.
And it's not only aerobic fitness as well.
If you have a look at other types of fitness, speed,
so this is sprinting or quick, agility tests or power,
power is normally measured by jumping, vertical jumping
or standing long jumps, we find exactly the same pattern.
And anything above the line here means these things
were improving.
Anything below the line means they're getting worse.
If you follow the red dots here
for the aerobic performance we see the cross
over year was 1970 as I've shown you.
Things got better until 1970.
In terms of speed and power things are still getting better
around 1990 but that started to get worse since then.
So it seems across the board in children's fitness,
there's been a decline at least over the last 10 to 20 years.
That's not happy news.
What about kids' fatness?
What's been happening to the fatness of children?
We're used to reading in the papers
that there's been an exponential increase in children's fatness
and one of our studies looked at that.
We gathered data on the skin-fold thickness.
Take a pinch of fat, the skin-fold thickness of children
about 500 thousand children from around the world
from about the 1950s onwards and this is the pattern that we got.
We had a look at their percentage body fat.
We see consistent and exponential increase,
at least until the mid-90s and perhaps up to the year 2000.
So you certainly get an increase there but if you look
at more recent data we're finding quite a different trend.
This study shows recent trends in the fatness of children
from a number of different countries,
on the X-axis here is the year of measurement.
On the Y-axis is the percent of children classified
as overweight or obese using a standard measure.
And each of these dots comes from an individual study
and the lines joining the dots show the trends.
And you can see here that these lines are basically flat.
There's been no change at all in the prevalence of overweight
and obesity in children in Australia
and around the world in the last 15 years.
So the rapid increase from the early 1990s onwards
and no change from about 1995.
This is true in almost every country we've looked
at are developed countries.
This study is of particular interest.
This is a study of 3 million low income children
in the United States.
So I think if there were any group
where fatness is still increasing it would be there.
It's not, it's basically plateaued.
If you have a look at Australian data,
we collected every study ever done since 1985 a total
of about 285 thousand children and we had a look at patterns.
And this shows the prevalence of overweight and obesity in boys,
this is the top level here, we had a look at trends from 1985
through to 1996 and then from 1996 through to today
and we saw there was a rapid increase
of about 1 percent a year up to 1996 and after
that it flattened out.
There was only a modest non-significant increase
after that, a similar sort of partner with girls.
The pattern was even stronger.
That was overweight and obese.
If we just look at obesity
by itself then we find similar sorts of patterns,
an absolute flat line after 1996 for boys
and the same sort of pattern for girls.
So around the world for reasons we don't really understand
there's been no change in the prevalence of the overweight
and obesity in children over the last 15 years.
Well, if that's so, even if there's no increase
at the moment there was a significant increase
from at least the early '80s probably before
that through to 1995.
So why is that so?
Why would that happen?
Well, it could only happen for two reasons.
It could either happen because kids are eating more
or because they were being less physically active
or a combination of the two.
So we set out to have a look at the trends
and the energy intake, the food intake of children
over the last 100 years.
I'd like to show you the data we've got here.
Certainly there's a common belief that the main cause
of childhood obesity is the increase
in energy intake particularly, the increase
in fats and saturated fats.
So let's have a look at what the data shows us over time.
The first study we did and this is a study
with my other student Joe Stevenson.
The first study we did was just to have a look
at all those studies which actually commented on trends
in children's energy intake over the last 10 or 20 or 30 years.
So these are just ones that made that comment.
And these are all the reports down the side here.
Now I'm just going to show you this section
in explaining this screen that here
on the X-axis here is the year of measurement.
On the Y-axis is the average energy expenditure
within each study expresses the average within that study.
So if I have three measurements of 90, 100,
and 110 the average is 100 there.
Now the first thing you notice,
the first pattern you notice here is there is no pattern.
They're all over the chart.
Some go up and down.
Some go down and up.
Some go up down up.
Some just go down.
They're really all over the place so this one for example,
is typical from the U.S. We've got data here
from Sweden showing a downward trend.
It's simply all over the place.
When you actually put them together it shows a downward
trend of about one percent per decade on average.
That really surprised us because we expected to see increases
in the energy intake of children.
So what we then did was to go back and look
at every study ever done which commented,
which reported the energy intake of children.
It did not have to comment on trends.
It just reported the energy intake of children
and we found 2,754 studies and the earliest one came from 1884.
I mean we had to look at how those studies
when we combined those studies the kind of picture it painted
and I just want to show you some of the data we got here.
We analysed these at the age, by sex, by country label so we had
for example, ten year-old Swedish girls
or 15 year-old Australian boys, collected all the data we had
and said what were the trends going on?
I'll just show you some of them here.
Let's have a look at U.S. boys.
Where you would expect U.S. girls even more you'd expect
there to be a downward trend here.
So if you have a look at 12 year-old girls and we plot
that each one of these red dots here is a study,
an individual study, and the line shows the trend
and you see the trend is a downward trend,
a decline of 4 percent in energy intake per decade.
If you look at 13 year-olds exactly the same pattern
in the United States,
14 year-olds the same pattern again.
Lots and lots of studies all showing the same downward
trend there.
If you have a look at Australian data, Australian boys
for example, we find either a flat pattern,
slight downward trend there for the ten year-olds,
similar for 11 year-olds, 12s down, 13s down a bit more,
the same sort of pattern there.
Now it was not the same everywhere.
Some went up but on the whole it was a downward trend.
Now just summarise those, to put those together in a single sort
of screen for you let's have a look
at Australian boys for example.
Anything which is red and above the line shows an increase,
historical increase in energy intake, anything which is green
or below the line shows a decrease.
So you get a mixed picture.
Some go up, some go down.
If you look at the United States
or the UK we're finding a predominance
of a downward trend.
In the U.S. for example,
for every single age group shows a downward trend.
So the evidence, I think is quite compelling
that let's just say the evidence
that kids are eating more is very weak.
I personally think there's compelling evidence
that kids are eating less than they have in the past.
If that's so, if they're eating less
but still getting fatter then there must be a decrease
in the energy expenditure.
Kids are less active than they have been in the past.
And the reduction in activity has outweighed the increase,
the decrease in food intake.
Well, you might say okay, well,
if kids aren't eating more they must be eating more rubbish,
so let's have a look at trends in dietary fats.
So once again we had a look at every study ever done
of the dietary fat intake expressed in percentage
of total energy intake from the '80s.
This shows from the 1920s onwards and this is the pattern.
Every one of these dots represents an individual study.
It covers about 300 thousand children in total,
and this is the pattern.
It shows that fat intake peaked at about 1960 about 40 percent
of total energy intake and it's dropped now
to about 30 percent over that time.
This is consistent finding by the way
for both adults and children.
So the evidence is that kids are not eating more
and they're not eating more fat.
They're diet might have gotten worse in many other ways
and that suggests to me
that their energy expenditure has dropped a lot.
Their physical activity has dropped a lot over that time.
Well, why is that so?
How is it that kids' activity has dropped
so much over that time?
And I think this screen provides a lot of the answers.
It shows for 14 to 17 year-olds in the United States,
historical trends over the 20th century in the number
of hours they spent at school and the number
of hour they spend at work
and the yellow line here represents school
and the red line represents work.
And you see across that time they spend in school
and work combined about 35 hours a week.
That's been pretty constant.
It hadn't changed much but the mix of school
and work has changed dramatically.
They hardly do any work at all.
And the reason is that most kids, my father for example,
left school when he was 14, went to work in a man's job
and it was not until 1963 that the school leaving age
in Italy was raised from 13.
So most 13 year-olds and 14 year-olds
in Italy would be working on farms and in factories
or in domestic work and their energy expenditure therefore
would be much greater over that time.
So I think the main reason for the shift in energy intake
and expenditure has to do with the change in mix of school
and work that kids are being involved in.
Let's move on to screen time.
Now screen time is one of the most cursed things
in modern society and I've got
to acknowledge there are actually some benefits
to screen time.
There's a suggestion that the increase in IQ,
the IQ increase is about 5 points per decade and has been
for about 100 years so it's pretty frightening
that your kids are going to be 15 IQ points brighter
than you are and you're probably 15 IQ point brighter
or do 15 IQ points better on tests of IQ than your parents.
And a lot of that is being put down to screens,
the fact that information comes so fast.
You've got to learn to process it.
The fact that we learn new visual graphical interfaces,
visual user interfaces, the matrix style way
in which information is presented
and there are other benefits too.
If it had not been for Thomas,
my wife is here, she can verify this.
If it has not been for Thomas the Tank Engine videos I would
have gone three years without ever having sex and even now,
even now when I hear the Fat Controller I feel a stirring
in my groin.
So it has advantages, screen time
but it also has a down side as well.
So firstly, where does the screen time fit
in the big picture?
Well, kids spend about 4 hours a day, about 16 percent
of their day in front of the screen of some sort
and two-thirds of that time in front of television
and the rest is pretty evenly divided between computer
and video games and the video games are almost entirely
passive video video games.
There's been a bit of an up-swelling in Wii
and Kinect and things like that.
They still constitute a fairly tiny proportion of the amount
of time that kids spend front of the screen.
So what's the problem with screen time?
Why is it an issue?
Well, one thing we know is that screen time is associated
with an increased risk of overweight and obesity.
We'll see in a moment that kids who are overweight
and obese get much higher screen times than kids who are lean.
And the prize mechanism for this looks something
like this firstly if you spend more time front
of the screen particularly television you're more likely
to snack.
Kids eat more snack food front of the television
and it seems they sort of pass, they don't notice
that it passes the observation threshold.
They're not eating mindfully during that time.
And of course while they watch television they're exposed
to ads for fast foods and energy dense foods as well
and that leads to increased energy intake
in the long-term and the short-term.
But screen time, that time has to be drawn from somewhere.
It's got to displace something
and to some extent it displaces physical activity.
So for every hour of screen time
in the data we have kids lose somewhere between 4
and 14 minutes of physical activity.
And that physical activity means
that it decreases energy expenditure.
When you've got decreased energy expenditure,
increase energy intake, you've also got one other thing too.
You've got long periods of sitting and long periods
of sitting has been associated with hormonal changes
and blood changes such as increase
in fasting blood glucose and a decrease in lipolytic,
in lipase, an enzyme responsible for storing and moving fat.
And all those things put together would increase.
So there's a good mechanistic flow chart there.
It makes sense that there should be a connection
between screen time and obesity.
And that's exactly what we find.
A second reason why we should be concerned about screen time is
that screen time is associated
with a lower health-related quality of life.
So what we did here was to have a look,
we used an instrument called the PedsQL which is the measure
of health-related quality of life
and basically how kids feel about themselves.
This is a psychosocial sub-scale so it's how well they feel
about themselves and how well they get on with others
and we had a look at kids who scored very highly
on that scale, high, low, and very low.
And we just had a look for the boys how much time they spent
in passive video games and these show the differences here.
So the kids who scored highly on health-related quality
of psychosocial life had low levels of video games.
The kids who scored very low had twice
as much time devoted to video games.
So there's a clear association between health-related quality
of life and video games in boys.
In girls there, the girls it was association, a bit weaker
but a significant association nonetheless between the amount
of time they spent in front of the television
and their health-related quality of life.
So those with the low health-related quality
of life spent more time in front of television.
Now we don't know which way that works.
We don't know whether it's because they feel bad
about themselves that they immerse themselves in the world
of war craft or whatever or it might work the other way,
that television is so depressing these days that they come out
and oh, I favour the later hypothesis myself.
So we are concerned about screen time
and so therefore guidelines have been set.
It's recommended that children in Australia, age 5 to 18,
get no more than 2 hours in front of a screen except
for educational purposes each day.
How many kids meet those guidelines?
Well, very, very few.
No matter how you measure it at best about a third
of kids meet those guidelines.
I think those guidelines are very unrealistic.
I don't think we have any hope at all of getting kids
to get their screen time under two hours.
I think the proliferation of the devices, the convergence
of different media make it very, very difficult to achieve that
but there are the guidelines as they stand.
So who watches more screen?
Is it all the kids, younger kids, fat kids,
lean kids, rich kids, poor kids?
This shows the relationship between age
and sex and screen time.
And what we find is that screen time peaks about age 13 or 14.
So if you've got a 13 or 14 year-old, hang on, there's light
at the end of the tunnel.
It will start to decline a bit thereafter.
It rises pretty steadily from about age 9 through to 13 or 14,
declines after that and the red dots here are for boys,
the yellow dots are for girl.
So boys get consistently more screen time
than girls in most media.
What about the household wealth?
Does that make any difference?
Well, it makes a little bit of difference.
If you have a look at computer time there's no difference
across the households.
We have like a video game time you see slightly
but not significantly increased times in all
but the wealthiest households.
And when you add television time we start
to find significant differences.
So kids from poorer households spend more time in front
of screens than kids from wealthy households.
That's a pretty consistent finding.
If we have a look at the difference between kids
from poor and wealthy households,
this is across the whole time use.
This is quite an interesting analysis here.
It shows across the entire gamut of time use,
what do rich kids do more of and what do rich kids do less of?
What we see is that poor kids tend to--
anything below the line poor kids are doing more of.
They tend to sleep a bit more.
They spend much more time in screen time, like television,
video games, no difference with computers.
So what do the rich kids do to make up for that time?
What are the rich kids doing more of?
Well, they're spending more time
at domestic things particularly, eating.
They sit down to eat meals with their parents.
They're with their families therefore they spend more time
doing that, a bit more time grooming.
They spend more time, as we mentioned before on sports,
team sports than non-team sports.
But what they spend most their time doing is studying,
school related activities.
And this is the one big difference between rich kids
and poor kids in this country.
They spend much more time at school related activities
and of course that affects their life opportunities right
through their lives.
So I think that's an important area to address.
There's also small differences in other types
of activities as well.
But essentially, there's a trade-off
in screen time and school time.
Kids from poorer families fill
in the school time they don't get with screen time.
What about weight status and screen time?
Is there significant relationships?
Yes, there are.
There's no difference in computer use.
There are no significant differences in video game use
but if you have a look
at overall television that's the big differentiator here
that obese kids get much more screen time
over an hour more screen time each day
than lean kids and thin kids.
That is a lot, an hour a day is 365 hours in a year.
That's pretty close to a quarter of a working year for an adult
that they sit in front of a screen.
That's a major difference, a major obesity related difference
in the way they spend their time.
Now we don't have much data on trends in screen time.
We don't really know whether kids are spending more time
front of the screen now than they were in the past.
We certainty suspect they are.
We only have data, our group,
only has data going back to 2000.
This shows the trends in screen time for television.
Total screen time in red, television in yellow,
blue we have video games and pink computer.
And these are non-significant trends.
We see no significant change.
There's a slight tendency for television to go down
and for computer and video games to go up.
I think that will be exacerbated in the future simply
because kids are not finding what's
on television very interesting and they can access
of much more interesting and varied content,
or indeed television content, from yesterday, today,
and probably tomorrow on their iPhones or on their iPads
or other convergent devices.
So we suspect that will be the trend in the future.
Let's finally move on to the big ticket item,
in time use and this is sleep.
So ten hours a day kids spend sleeping and it really is,
it's like one of the dark matter of use of time universe.
We know it's important.
We know there's more of it out in there somewhere
but we're just not seeing it ourselves.
What's happening with kids sleep?
Who sleeps and what's the importance of it?
The first thing to say about kids sleep is
that a pretty large proportion of kids are not happy
with the sleep they're getting.
These data comes from the Health of Young Victorian Study
which is a study led by Melissa Wake
from the Murdoch Children's Research Institute
and it just look at the percentage of respondents
who said they found their sleep quantity, that's in red,
very good, good, fairly bad, or really bad.
These are my kids here by the way.
They sleep very well, too well.
Most kids are fairly happy with it but you see about 25 percent
of kids rated their sleep quantity
as being bad or very bad.
And if you look at sleep quality we find the same sort
of patterns.
So roughly one child in five around Australia is unhappy
with the amount of sleep they're getting.
They think they should be sleeping more.
And I suspect most parents think their kids should be sleeping
more as well.
What's the problem with not getting enough sleep?
Well the answer is basically everything.
So that inadequate childhood sleep has been associated
with the whole suite of negative health implications later
on in life.
It's been associated with greater risk
of sociopathic behaviour, of alcohol and drug addiction,
of suicide, of depression.
We know that acutely restricted sleep causes immunosuppression.
It increase your susceptibility to opportunistic infections
such as colds and viruses.
It's associated, in particular, as you'll see in a moment
with the greater risk of overweight and obesity.
It's also associated with poorer school performance.
It's a very simple study.
It's from the United States.
They had simply asked kids when they went to bed on school days
and non-school days, a usual school day, non-school day
and whether they normally got As or Bs or Cs or Ds
or Fs on their grades.
And this shows the pattern here.
The kids that reported they got As typically went
to bed much earlier both on school days and non-school days
than kids who got lower grades.
This, by the way, is an American study but look
at the bedtimes here, even the kids that got
As are going to bed at midnight.
These are kids, I think 14 to 17 from the States at midnight
and the other ones are going to bed at 1:30 in the morning,
so very late bedtimes there.
Bedtimes in the U.S. are generally much later than here.
And American kids sleep less,
about an hour less a day than Australian kids.
So there's big differences there.
And the lowest sleep is of all are the Japanese.
The Japanese and Chinese have very low sleep times.
So it's important for school performance.
It's important for a whole range of things, short-term memory,
memory consolidation but also scores on standard tests.
Now this particular study, that's an American researcher,
and he got kids under two conditions in sleep laboratory.
In one condition he had them in bed for 11 hours.
They did not actually sleep the whole of 11 hours
but they had 11 hours of sleep opportunity and he tested them
on a test called the Torrance Test of Creative Thinking.
It just shows degree of flexibility and ingenuity
and creativity and the way you think.
And these red bars here show the scores
when they had 11 hours of opportunity sleep.
They slept I think, on average for about 9 and a half
or 10 hours of their 11 hours.
And then he restricted their sleep.
He only gave them 5 hours in bed.
So acutely restricted sleep
and the yellow bars show their scores with just the 5 hours
and all of these tests, all but one, I think,
there's significant difference.
There's a definite drop in performance on their tests
of creativity and intelligence and so forth
when these kids had their sleep restricted, acutely restricted.
But most studies show the same sort of thing.
That applies not only to memory of things they learned,
you know, the capitol of China and so forth.
It also applies to motor learnings.
So when they learned a sports skill,
they're learning is impaired unless they have a good sleep
after they've learned it.
From this particular study they learned a motor task.
That's the training and they were tested.
That was 9 a.m. They were tested at 10 a.m.
and at 10 p.m. the same night.
Then they had a sleep and they were tested again
at 10 a.m. the next day.
So they wanted to see whether having sleep
by itself increased their ability to perform this task.
And this is their score on the task.
So after the first training session they had a score
indicated by the yellow bar.
It increased a little bit after a 12 hour wait but it was only
after they had a good sleep that night
and were tested the next morning that you got a rapid
and significant improvement
in their ability to perform that task.
And they tried it with different combinations.
Here for example, they had the sleep immediately
after they learned the task.
There's the learning and once again you got a much better
performance on the task after the sleep.
So sleep is important for memory consolidation, not only of facts
and things of that sort but also for motor tasks as well.
So certainly sleep is important.
This is overwhelming evidence
that sleep is very important for kids.
As I mentioned sleep's been associated with the greater risk
of overweight and obesity
and there are good mechanisms for this.
It could be that fatness causes poor sleep through mechanisms
such as sleep apnea, difficulty in breathing when you're asleep.
It could work the opposite way,
that reduced sleep causing fatness and some
of the mechanisms here are hormonal changes,
there have been changes in thyroid stimulating hormone
in thyroxin, in hormones which regulate appetite
such as ghrelin and leptin.
So there are great mechanistic reasons for believing the kind
of hormonal disruptions we get
when sleep is restricted could lead to weight gain
or it could be some third factor.
For example, kids who stay
up late may increase their screen time
and decrease their physical activity.
So we don't know exactly what the causes are
but we do know there's a strong association
between short sleep and obesity.
And this just shows three studies.
The first study is a French study by Locard
and he just had a look at the odds ratio,
the risk of being obese for kids that got more than 12 hours
down to less than 12 hours sleep and he found that kids
that got less than 12 hours sleep had a greatly increased
risk of overweight or obesity, roughly five times the risk.
A similar sort of study from Gupta, 11 to 16 hours
in the United States high versus low sleep greatly increased risk
of overweight and obesity, and a study by von Kries
from Germany just had a look at the percentage of children
who are obese who got low amounts of sleep
and high amounts of sleep
and it was roughly three times greater percentage of kids
in the low sleep zone than in the high sleep zone.
So the evidence is pretty consistent
across different countries and different studies.
Well, who gets sleep in Australia?
What happens with age and sex and so forth?
Well, a number of different studies, one of our studies here
in blue, a French study by Bresard and a Swiss study
by Iglowstein show the same sorts of patterns.
Sleep declines with age.
It declines on average at about ten minutes per year.
So, ten year-old kids get about ten hours sleep.
Eighteen year-olds get about eight and a half hours sleep
on average, across school and non-school days.
It also changes according to the kind of day.
So a typical pattern, particularly as kids get older,
is had they sleep less and less on school days
and have big catch up sleeps
on non-school days particularly Friday night and Saturday night.
So here we looked at different day types.
These are days when they wake up on a school day and go to bed
on a school day down to when they go to bed and they wake
up on a non-school day and go to bed on a non-school day.
And this is the pattern that you get.
So typically this is a Monday, Tuesday, Wednesday,
Thursday pattern, Friday pattern,
Saturday pattern, Sunday pattern.
Sunday is the day when they get the least sleep.
Sundays you'll see is the problematic day
for sleep for children.
It's what distinguishes sleep patterns in kids.
If we have a look at the average amount
of time here we see the difference between days
when they wake up on a school day and days when they wake
up on a non-school day, so Friday night
or Saturday night is 41 minutes, a big difference in sleep there.
So when they wake up on a school day they get much less sleep
then they do when they wake up on non-school day.
This shows sleep time and how it changes with age but bearing
in mind these different types of days.
So if you have a look at non-school, non-school days.
These are the weekend days like Saturday or Sunday.
We find it hardly changes at all across age.
So 10 year-olds sleep just as much
as 18 year-olds on these days.
But on the other days there's a rapid decline with age.
On school days the rate of decline is 15
to 17 minutes per day across that time.
So there are different rates of change according
to what type of day it is.
There are small differences in sleep according
to the socio-economic status of the household.
So we find particularly, on non-school, this is a Saturday,
here on Saturdays we find the kids
from very rich households sleep more
than kids from poor households.
And I think a lot of these patterns we're seeing represent
the kind of regulation or control or routine
that exists more in rich households
than in poor households.
In poor households, often single parent households there's not
that control, there's not that regulation and routine.
It's a major of the chaos,
if you like that you find in these households.
We also find differences in sleep across people
with different weight status.
And this is particularly true on the Sundays here.
This shows the pattern on Sundays.
You see that these kids here get more than 60 minutes less sleep
on Sunday nights than kids who are very thin.
Sunday night is the big discriminator.
If you could intervene just
in one day it would be Sunday nights you would intervene.
Get the parents to get kids to go to bed earlier
on Sunday nights the world would be a much better place.
Parents would have more chance to have fun.
Well, are kids really sleeping less?
Everyone thinks kids are sleeping less.
Everyone thinks this.
We decided to have a look at the literature.
This is done by one of my honour students, Lisa Mitchrichoni
and initially, we just had a look at all those studies
that dealt with the energy intake, the food intake,
all those studies which commented on trends
in kids sleep and we found about 54 studies I think
and every single one of those studies said
that kids were sleeping less than they used to.
But when we looked at the evidence they provided
for that we found that it all came
down to just two actual studies.
They all referred eventually to two studies.
One was one study which we did which had a look at changes
in the sleep patterns of kids in Australia on school days
and another was a study which looked at sleep in children,
37 children in the United States measured in the late 1930s
and compared them to a group of children measured in 1995.
That is all the evidence they had
for declines in children's sleep.
So we decided to go further
and once again find every single study ever done of the sleep
of children and we found data on about 700 thousand children
from 20 countries around the world
and these are the patterns that we got.
This shows the change in sleep over the week.
This is in minutes per year, so that each year
over the last 100 years kids have been sleeping 45
seconds less.
These differences are most found in older kids
than in younger kids, so older kids have been losing
about a minute of sleep each year.
It doesn't sound like much, 45 seconds a year
but what it means is that your kids will be sleeping 25 minutes
less each day than you did when you were their age
and those kids will be sleeping 50 minutes less each day
than their grandparents did.
So it's quite a dramatic change in the amount of sleep they get.
That's close to 300 hours of sleep a year
that they've lost in two generations.
So it's a rapid change in the sleep of kids.
And two things we know make this possible.
If you have a look at the amount of time
that countries spend sleeping, there are two big determinants.
One is electricity and the other is coffee.
So there's a direct relationship between electrification
and the caffeinisation of societies.
Caffeine now makes it possible for us to stay up
and electricity gives us something
to do if you do stay up.
This is the Australian study which we did.
One of the studies that was cited in literature
and we just had a look at compared data from 1985 to data
from 2004 and it just shows,
this is the bedtime, over this time.
And so the leading edges are the bedtime and this is wake-up time
for boys, girls, and all kids.
We see that across the board they've lost about 30 minutes
of sleep over those 19 years
but the sleep is entirely lost in bedtime.
They don't get up any earlier, they go to bed later.
And that's an event you find all over the world.
It's later bedtime which is causing lower sleep.
Well, one interesting question we should ask is all this due
to not having enough sleep or is it just the fact
that kids are going to bed later?
And we conducted a study to have a look at this
and what we did was to get data on about 10 thousand kids
who knew their bedtimes, their wake-up times, their sleep times
and we divide them into four groups with the early,
early group, this is early to bed, early to rise group.
So they went to bed on average at 9:20,
got up at three minutes past seven.
These are age adjusted, by the way,
they had about 9 hours 43 minutes sleep.
The early to bed, late to rise group, this is the group
that got the most sleep, over ten hours.
The late to bed, early to rise, this is the group
that got the least sleep, and finally the late
to bed, late to rise group.
Now the interesting thing
about this group although their bedtimes were
about an hour later and their rise times were
about an hour later they got almost exactly the same amount
of sleep, within a few minutes, as the early
to bed, early to rise group.
So we wanted to compare the early to bed, early to rise
with the late to bed, late to rise, same amount of sleep,
bedtimes and wake times differ.
Does it make a real difference?
And the answer is yes.
So if you had a look at the percentage of children
who are overweight and obese in these different groups we found
that the late to bed, early to rise, late to bed,
late to rise were significantly more likely to be overweight
or at least 30 percent as opposed
to a little bit over 20 percent.
So that's in spite of having the same sleep duration the bedtimes
are a critical thing, similar sorts of other patterns
with other measures of overweight and obesity.
They're at greater risk of being overweight or obese
and their standardised weight
for height score is also much greater.
So what is it about it?
Well, one thing we found was there was different exposure
to physical activity.
So kids who were late to bed,
late to rise got much less physical activity than kids
who were early to bed, early to rise when we measured
that in minutes, this is the number of steps
that they took using a pedometer.
This is minutes of reported physical activities,
same sort of pattern, a similar sort of pattern
when we had a look at their daily energy expenditure.
When we took sleep out of the equation,
exactly the same sort of pattern there.
So it's the late to bed, late to rise group had less
and the odds ratio for having low physical activity was much
greater for the late to bed, late to rise group,
similar sorts of patterns with screen time.
So the kids who were late to bed,
late to rise had much greater screen time, spent more time
on the computer, video games, screen time in general,
and were at much greater risk
of not meeting the guidelines for screen time.
But a less interesting study, something we've just published
and we had a look at the energy intake, the eating habits
of kids who were late bedtimes
and this shows the number of bad extras.
This is basically junk food or snack food they had
and you see the kids who were late to bed
in both cases had a much higher intake of junk food than kids
who were early to bed, early to rise.
There were non-significant trends in vegetable intake
and trends in fruit intakes,
significant trends in fruit intakes.
So they had a worse diet.
So what's going on here?
If I put it all together I think it works like this.
This is the kids' diet.
They start off and basically they have,
the kids have breakfast.
Breakfast is normally a nutritionally,
a pretty good meal.
It normally has a bit of fruits, some cereal, some milk.
It's nutritionally pretty sound.
It's the late night meals where kids eat fast food.
They snack a lot and so forth.
So if you have a look at the, and also in the mornings
when the kids do their physical activities they go off
and do their swim classes or their early training
or they walk to school, whatever that's when they become active
and at night is when they get the screen time.
They play video games.
They watch television.
So if you look at the early, early pattern.
The early to bed, early to rise these are kids
that get all the good things in the morning.
Great opportunity for physical activity, much better,
much sounder nutrition and they miss out on the bad things
at the end of the night.
If you look at the late, late pattern
on the other hand, we find the opposite.
They miss out on the good things.
They don't have time to eat breakfast.
They go off to school without having done any
physical activity.
They wake late and they're driven to school
to get to there on time.
At the other end of the night they have much more opportunity
to eat fast food and to snack
and to accumulate high levels of screen time.
I think that's what's happening.
I think the critical thing is not so much sleep duration,
the critical thing is bedtime.
So if there was one thing which I would advise parents to do is
to do everything they possibly can to get their kids to go
to sleep early on Saturdays or Sunday nights rather.
Now one solution is, just to finally wrap
up with a suggestion of how we might deal
with this sleep issue, one solution is to have a look
at school starting time.
So there's a big debate on in the United States at the moment
as to whether the schools should start later for older the kids
because you know what happens
with older kids is they have what's called the phase shift.
So you've probably noticed yourselves that sleep comes
in waves, waves of about 90 minutes.
You get very, very tired.
You get through that wave then you begin to feel okay,
90 minutes later another wave hits you
and it's actually difficult to go to sleep if you get
through one wave you're alert and everything.
Well the same happens with kids but what happens
at puberty is the phase sift is set back one wave.
So at 9 o'clock they're just not tired.
They only get tired at 10:30 or 12 o'clock
when the next wave hits.
And this is due to hormonal changes or changes
in the hormone melatonin.
It's a physiological thing which is associated with puberty.
There's not much we can do about it.
They're simply not tired at night yet they have to get
up the next morning to go to school.
Every child, almost every child in Australia gets up between 7
and 7:15 on school days.
There was a terrific study done across the U.S., Canada,
and Australia which had a look at how much time it took
between a child waking up and the time they left the door,
went outside the front door to go to school
and every country was exactly 82 minutes.
That's what it takes to get a child up, get them fed,
get them awake, get them toileted and you know,
get some is food into them,
make sure they've got their books and send them off.
So these kids go to bed late because they're not sleepy.
They have to get up early because they've got to get
to school so the idea is just start school time later.
So what's the evidence that late school time does any good?
Well the evidence is pretty good.
There's this terrific study that was done
at the U.S. Armed Forces Academy
where they control for everything.
And they basically had three different conditions.
They rotated the lecturers and they rotated the conditions
for them and they had a start of 7 o'clock, 7:30, and 7:50.
Schools in, by the way, the United States start much earlier
than schools in Australia, not normally this early,
this is an Armed Force Academy but schools start times
in the States are typically 8 o'clock, 8:30.
And it shows a clear difference in academic scores.
Academic scores improved as school start time is put back,
even by small changes of 20 or 30 minutes.
Similar sorts of results in this study here
by American Paediatric Sleep Researcher Judith Owens,
and it just shows the percentage of children,
they did a randomised, a trial where they started these kids
at 8 o'clock and this is the percentage of kids
that reporting they are too tired
for school work, too tired for sports.
They fell asleep in class.
They arrived late.
Interesting, almost all children say they're too tired
for school work.
But when they put it back to 8:30 this is the result
that they got so big and significant drops
across the board in all these things.
So kids reported three felt much better.
And objective major such as the number of kids not turning
up at school, the number of kids who went to the nurse
for sickness, and so forth also dropped off as well.
So the evidence seems pretty clear
that delaying school times will help a lot.
Another inventive techniques used, we know that one thing
that can reset your phase shift is to expose you to bright light
and one of the theories is the reason why the kids this phase
shift is they're exposed light of screens,
particularly the blue light of computer screens.
But if they're exposed
to a bright white light you can actually reset the phase shift
and so what they tried to do in this study is in schools
to expose kids to bright white light hoping it would reset
their biological clock and they used a placebo
which was a red light.
The red light does nothing it's only the bright blue white light
which is supposed to work.
And they tested two measures of mood how energetic they if felt
and how their mood would say in general and this shows the pre
and post scores were bigger when they used the red light
and there was no significant differences there
and that was what you'd expect.
It's just a placebo that doesn't do anything.
And this is when they used the white light these are
in the yellow bars here.
So they found tragically,
that once again there was absolutely no significant
difference at all.
So it didn't work in the least, neither the exposure
to the red light or to the other white light works so we're back
to looking at school times there.
Well, taking a pretty quick trip and a pretty in depth trip
through these three activities, through physical activities,
screen time, and sleep it's interesting some years ago I was
at my kids primary school and they had a sleigh
of the old textbooks they used and I picked
up the hygiene textbook from 1927
and the first thing I learned was there are three important
ingredients for a child's health.
They should get plenty
of physical activity in the open air.
They should eat lots of fruit and vegetables
and they should get lots of sleep.
And so in those 85 years we've really made no advancement
at all.
It's exactly the same advice which I give now.
I just want to finish by thanking, these are just some
of the people within the team.
Almost all of the data I presented here is not my work.
It's their work so I want to thank those.
Thank very much.
[ Applause ]