Science series. Dallas Campbell downs his toothbrush to discover what causes tooth decay and gum disease, and Dr Yan Wong explains why refreezing food is not a great idea.
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Tonight, Jem takes part in an experiment
to discover how electric light
may be playing havoc with our sleeping patterns.
It's morning light that is so important
for setting the body clock.
OK, this is it. This is truly grim.
And Dallas downs his toothbrush
to find out exactly what causes tooth decay and gum disease.
-Have a smell.
-Eurgh! It's stinky!
That's Bang Goes The Theory, revealing your world with a bang.
Electric light, something we take totally for granted.
The flick of a switch, we get ourselves some indoor sunshine.
But worryingly, scientists are beginning to understand
that living under artificial light may have an unexpected effect on our bodies.
No one really knew why until a recent discovery
revealed a whole new way in which our eyes work.
Our eyes are one of the best-studied organs in medical science
yet only recently did we discover they do far more than simply see.
Just a few years ago, researchers at Oxford University
found that our eyes have another, subconscious response to light,
one that deeply affects our daily lives.
If only I could get through this impossible dark room door.
I'm going to find out how it works from the man who discovered it,
Professor Russell Foster.
OK, I'm going to plunge you into darkness now.
OK, that's pretty dark now.
Professor Foster starts by demonstrating
the two ways our eyes consciously see.
These are the classic tests to find out if you're colour-blind.
Exactly. Can you recognise any numbers in there?
I could tell you it's black on the outside, then sort of white there,
and this is neither black nor white, but actual colours, there's none.
It's just shades.
So I'm now going to increase the light a little bit.
Now you can tell that there's like reds and browns appearing
and then there's sort of greens and blues.
-I'm going to go for that as a six.
-The most important part of the eye
are the light sensors or the photoreceptors.
There's the rods, which are used for dim light vision.
They're essentially brightness detectors.
And then the cones, which allow us to see colour.
In fact, there are three different types of cone in our eye.
Each of those cones is peaking broadly in the blue part
of the spectrum, the green part of the spectrum
and one in the orangey red part of the spectrum.
When you stimulate all those three receptors maximally,
as you would with sunlight, it appears white.
So to make artificial sunlight, surely all you need is to fool
the eye with the right mix of red, green and blue, isn't it?
Well, that's what we'd assumed.
Until Professor Foster made his stunning discovery.
A third type of light sensor in our eye.
A colleague came across a lady who had a very strange visual defect
whereby she'd lost all of her rod and cone cells.
She said she had no conscious light detection but we said,
"OK, just tell us when the lights were on and off." And quite remarkably, she could always do it.
-And so there's another, yet another light sensor in the eye.
Not the rods and not the cones, but it's a group of ganglion cells.
They have a peak in sensitivity in the blue part of the spectrum
and it's at a colour or a wavelength which basically matches
the blueness of a blue sky.
These special blue sensors are nothing to do with actually seeing.
We thought of these new receptors in the eye as body clock light sensors.
We have an internal body clock which is constantly adjusting
and fine-tuning every aspect of our physiology.
So it contributes to your overall alertness, your ability to constrict your pupil,
adjust your body clock, and probably a whole raft
of other things we're just discovering.
The Professor thinks these sensors evolved in our early ancestors,
allowing them to take subconscious time cues from sunlight.
And they worked perfectly, until engineers like me got involved.
For millions of years, the only lights we had, really,
were sunlight and firelight.
But with the advent of electricity, things changed fairly dramatically.
This electric arc actually gives off pretty good fake sunlight.
Look, if I split up its colours. It's a very even spread on the spectrum.
We've got red, yellow, green, blue, right the way up here.
It's almost identical to the range of colour in natural sunlight
with plenty of that blue that your body clock needs.
Trouble is, it's far too bright to use at home.
Plus, it's full of dangerous ultraviolet. Protective masks indoors? Just not a good look.
So I'll move on swiftly, just like mankind did,
to this, the incandescent bulb, the kind of standard lightbulb.
Electricity can make a thin wire very hot
and at a few thousand degrees, it'll start to glow white hot.
But this is no ordinary wire, this is tungsten wire,
which melts at well over 3,000 degrees Celsius.
I have to put a glass over the top of it,
and suck the air out of it, so that wire doesn't burn when it gets hot.
There you go. It's now sat in a vacuum.
There we go. That is a lightbulb. It's like a miniature star in a jar.
Although this looks like sunlight, the mix of colours is not the same.
It has less in the way of blue and violet in it
than maybe bright daylight would have, so in light like this,
there's less of the colour those sky blue sensors respond to.
But traditional bulbs like this are too inefficient for moderate use.
Making artificial light through extreme temperatures,
it requires a relatively large amount of power for not that much light.
So in our energy efficient modern age,
we've moved towards lamps that operate
from an entirely different phenomenon.
Fluorescent lights work a bit like the Northern Lights,
where electrical energy gives the sky an eerie glow.
I'm pumping the air out of this tube to recreate the upper atmosphere.
A blast of a few thousand volts should make that low pressure air
produce an almost magical effect.
Look at that. I mean, it's a weird, pink light,
as you may expect from a kind of home-made aurora.
Of course, it's not magic. It's atomic emission of pure cold light.
I'm pretty chuffed with it. Though it's not much like sunlight yet,
but I can fix that. How do you go from that beautiful pink
to the classic white fluorescent we're used to?
Well, what you have to do is coat the inside of the tube with a powder,
a mix of chemicals called phosphors
that gives off a whole range of colours
when stimulated by the UV light that's also given off by those atoms.
Let's see how this goes.
It's a pretty white light.
All strip lights work like this,
and it's what's coiled up inside low-energy bulbs.
It's still made up of different colours, but this time,
instead of it being a smooth spectrum from red to violet,
instead it's distinct bands of colour.
The different bands are produced by different glowing powders.
Now, you only need a few bands to trick the eye into seeing white,
but unless the right sky blue is there,
there's nothing for those newly discovered receptors.
Our modern lives are a jumble of different artificial lights
and it could be playing havoc with our body clock.
I'm going to do a little experiment and I think it's a world first.
I'm going to see how much of that blue light
I'm exposed to over a typical 24 hours and when.
Which means carrying this kit around with me
to analyse the spectrum wherever I go.
I'm hoping Professor Foster can tell me what all this
might mean for my body.
OK, Jem, so what we've looked at here is the amount of light
in the blue, the blue skylight at 480 nanometres.
-It's very clear that you went outside just after nine o'clock
and the light levels have just rocketed.
-They've gone absolutely huge.
-I cycle to work.
It takes about half an hour. This day, I had to pop out and do a bunch of other stuff as well.
And that's really important, because it's morning light
that's so important for setting the body clock. So, wittingly or not,
you've seen light during the most important part of the day.
So in the winter, when you're kind of going to work and it's dark
and it's just getting light as you go into work quite often,
are you effectively giving yourself jetlag?
Your body's not sure what time of day it is.
There's increasing evidence that's exactly what we're doing.
I think there's an opportunity here. In the underground,
in the tubes, we could have augmented lighting,
we could actually try and provide a brighter morning light environment,
-which would help stabilise internal time.
-Anything that makes travelling
on the tube slightly better for you is a good thing.
During the day, I'm only getting bursts
of that all-important blue light when I go outdoors.
So what's the deal with the artificial lights I'm using?
-Here I am in the workshop.
-Oh, my goodness.
This has got to be fluorescent light. You can tell that
because of these sharp emission spectra in the blue,
the green and the red, but you've got very little blue.
So not only is it low, but it's actually lacking in blue light, which is what you want.
Is there an effect on me of having such low light levels at work?
The loss of blue light would have a distinct effect
on your levels of alertness.
Fluorescent lights give off very distinctive colours.
-But they're not the only lights in my life.
-So what time of day?
-This is midday.
-It's strange, because it's not fluorescent light,
cos there's no great big peaks. Is this a computer screen perhaps?
It's like talking to Derren Brown.
Yes, that probably is a computer screen.
You've got a nice blue enrichment there,
which means that if you were looking at a computer screen like this
at night, before you're going to bed, that blue enrichment
could actually increase alertness and so significantly delay
your tendency to fall asleep and go to bed.
My lights at home are different again. Can he identify those?
You don't have any big peaks in it, so it's not fluorescent light.
But it could be something like a halogen light,
and so you see the broad tungsten light,
relatively enriched in the red compared to the blue.
-You've got those little halogen lights?
-Yes, I have.
So if I wanted lighting in my home to make me feel alert,
or at work, to make me feel alert, I'd be looking to have
lighting that had a high enough proportion, and a high enough
intensity of this blue, but then I wouldn't want too much of that
in the evening, otherwise I'd stay alert when I wanted to go to sleep.
Exactly. And this represents a huge problem
for people who don't get out very much.
If you're in a nursing home, with relatively dim light,
you'll never get that bright exposure and the body clock
will tend to drift through time. And also the various rhythms,
so the rhythms that regulate your gut function or your brain function
or your liver function will then start to drift apart slowly,
and so you won't have very fine-tuned
and well ordered physiology under those circumstances.
I think that is a really, really interesting film.
Off the back of that, there's obvious things you can do to help.
Don't be looking at your computer before you go to sleep,
and if you can, in the morning, go out and get a bit of sunshine.
It makes sense. But armed with that knowledge, presumably we can start to develop
technologies that are geared to how we've actually evolved,
because clearly, as a species, we're not evolved to live
-in the world we've created for ourselves.
-You're bang on the money.
There are companies out there at the moment that are actually
developing artificial lights that change their spectra during the day
to sort of match what daylight does.
My view, though, no substitute for daylight.
Although our eyes adjust brilliantly to different light levels,
it can actually be thousands of times brighter outside
-than under domestic lights.
-You can't beat the sun.
But in a country like this with pretty grim winters,
anything you could do to help you feel better is a good thing.
For example, I do feel really rubbish in the winter,
so I bought a seasonal affective disorder lamps, you know those?
But after watching your film, I've realised why I was disappointed.
I was using them in the evening after college,
from seven to 11 o'clock or something,
and now I know to have used them in the morning
to actually kick off my body clock, yeah?
Exactly. The strong morning light makes the biggest difference.
Interesting stuff there. Next up, it's Dr Yan.
He's in the kitchen this week talking about refreezing.
We've all been there. You take out a frozen chicken dinner
and you don't eat all of it but you know not to refreeze it.
But do you know exactly why that is? Dr Yan is about to explain all.
Using six chicken breasts, a punnet of strawberries and some fresh carrots,
I'm going to get to the bottom of this domestic dilemma.
These two, I'm going to put straight back in the fridge.
These two I'm going to leave on the side. But these, well,
I'm going to put them in the freezer now but I'm going to defrost them
and refreeze them every day for the next five days.
The carrots and strawberries I'm going to put in the freezer, too.
That's not the normal place for this stuff but it'll all become clear.
Now all I need to do is wait.
Right, this should be done now.
We all know that water turns solid when it freezes.
It forms rigid crystals of ice.
Well, 75% of this chicken breast and in fact, 90% of these,
actually is water, so these are basically just solid blocks of ice,
and ice crystals can be nasty things if you're a carrot.
Food like this is made up of individual cells.
Imagine them as tiny balloons filled with water.
When they're not frozen, they keep the carrot nice and crunchy,
but that all changes when the cells begin to freeze.
Now, ice crystals inside the carrot act like microscopic needles,
puncturing the cells.
While it's frozen, you don't notice any difference,
but as it defrosts, the water all oozes out.
Which leaves the cells saggy and empty
and us with a floppy, leaky carrot. Eurgh.
And the strawberries, well, they're even worse. Look.
The effect on meat is not nearly so severe
but the same principle applies. But that's just it.
It's only physical damage. Not very nice to eat, maybe,
but totally harmless. There is something else
we need to worry about, though. Bacteria.
We all know that harmful bacteria on food can give you a dodgy tummy.
On something like this, you could easily expect there to be
10,000 bacteria per square centimetre.
But under the right conditions, bacteria can quickly multiply
to 10 or even 100 million per square centimetre,
and that's when they're likely to make you ill. So does freezing,
thawing and refreezing chicken make the bacteria any more harmful
than just leaving them in the fridge or out on the side?
Here we go. Every morning for five days, I'm going to take the chicken
out of the freezer to defrost and every night put it back in again
to refreeze. Then, I'm sending my refrozen chicken breast,
along with the one I left in the fridge
and the one that's been at room temperature the whole time, to be tested at a lab.
Now, here are the results.
The lab wouldn't actually send me back the samples
because they were so contaminated, but this is what they found.
Any coloured spots you see are harmful coliform bacteria.
These are the results from the fridge chicken. There's not that many spots.
There's a pair there and another two spots there
but, you know, that's not that many. I'd probably eat that one.
Here are the results from the chicken left out on the side.
Loads of bacteria. The blue one is E.Coli. You've probably heard of it.
You don't want to be eating lots of those. They thrive in a danger zone
between five and 55 degrees Celsius.
Now for the moment of truth. My refrozen chicken.
Whoa, look at that, there's loads of coloured dots.
There's fewer red ones than in the chicken left out on the side
but there are three E.Coli there and, together with the others,
enough to make you ill. The temperature's made the difference.
Every time this chicken was defrosted, parts of it
entered that temperature danger zone, from the first few minutes.
And they stayed there until the chicken was put back in the freezer
many hours later, allowing the bacteria to multiply the whole time.
So it's not the freezing or refreezing that's the problem,
it's the time the bacteria spend in the danger zone
while the food defrosts. And it's not just raw meat, either.
The same applies to re-freezing old cooked food.
The bacteria will still be there lying in wait.
I've just noticed a really interesting phenomenon.
Dr Yan, he's done a few experiments in kitchens
over the last few years, and every time, he's in a different kitchen.
-Not only is he a brilliant scientist, he's also a property magnate.
-Nothing would surprise me about Dr Yan.
What I didn't quite get, surely with all those bacteria,
once you cook it, get it to a couple of hundred degrees,
-it kills the bacteria anyway?
-The heat does kill them
but it's not the bacteria themselves that cause illness,
it's the toxins they release as they're metabolising in your body.
So, for example, nasty E.Coli. You can kill the actual bacteria
in the heat of the food, and you can break down some of the toxins that it produces, but not all of them,
-and it's the remaining toxins that make you ill.
We're going to stay on the Dr Yan lovefest theme.
Here is his weekly brainteaser. What is this?
-The moon on a piece of paper.
-Not the actual moon, a picture of it.
Very bright. That's not actually the conundrum.
How many times would I have to fold this piece of paper in equal parts
in order for it to be able to reach that moon 250,000 miles above me?
That's maybe 0.1mm thick. You are looking at thousands
of trillions of times thicker. I don't even think you could do it.
It's fewer than you think because actually, it's an exponential.
Cryptic clue. The answer's actually the answer to the ultimate question.
If that's confused your brain like it has mine, don't worry,
Dr Yan explains it perfectly well on our website, as always, /bang.
OK, coming up next, it's oral hygiene.
Now, like most people, I brush my teeth twice a day
to avoid getting fillings, but it turns out
that the main cause of tooth decay isn't due to lack of brushing.
And if you don't believe me, I've got 2,000 years of evidence to prove it.
Meet my three new friends, all former London residents.
This is a female Roman skull and if you look at the teeth,
there's a bit of wear and tear, but no tooth decay at all.
Surprisingly, very good condition. Fast forward to a mediaeval skull
and despite the lack of electric toothbrushes at the time,
again, very good teeth, no sign of any decay.
Cut to a post-mediaeval skull, and it's not pretty.
You can see here, very bad tooth decay. An abscess here.
It's not looking good. But why is that? One word, sugar.
This person's generation was the first in history
that could easily get hold of it, and they loved it.
And although they were probably no worse at brushing,
the sweet tooth alone was enough to set in the rot.
Allow me to demonstrate with this tooth-shaped cake.
When you eat something delicious and sugary like this,
it's not just you that gets a treat,
because inside our mouth, it's full of bacteria.
Most of the time, it's harmless and causes us no trouble.
Until, that is, you decide to eat or drink something sugary.
The bacteria thrive on sugar and as they digest it,
they create acid as a by-product.
It's this acid that is the problem because as it bathes the teeth,
it starts to dissolve the enamel.
This process is called demineralisation
and it happens every time you eat or drink something sugary.
Enamel is actually one of the strongest parts of the body,
but under attack from acid, mineral ions are removed
and that lattice structure is weakened.
If it continues to come into contact with acid,
eventually it'll collapse and that's when you get a cavity.
The acid gets to work in minutes.
Brushing at night can't undo the damage,
while brushing straightaway can even make it worse.
Thankfully for us, we have a natural weapon against tooth decay.
It's called saliva and it helps to neutralise
and wash away that acid, but it also contains mineral ions,
replacing the ones that are lost through acid erosion,
remineralising and helping strengthen
that latticework structure of the teeth.
But if you keep on eating sugary snacks,
your saliva can't keep up with the repair work.
What starts as a small cavity gets deeper and deeper.
And if the cavity expands and reaches the inner,
living part of the tooth, the dentine,
it's going to get painful because that's where your nerves are.
Most of us at this point are going to consider a trip
to the dentist, but if left unchecked, you're going to get
full-blown tooth decay and, eventually, your tooth will fall out.
The best way to avoid decay, then, is to avoid sugar.
So what's with all the brushing?
I'm going to find out by hanging up my toothbrush for five days.
OK, this is it. This is truly grim.
This is the last time I'm going to brush my teeth
for the next five days, so don't come anywhere near me.
It's day three. This is the third day I haven't brushed my teeth
and people are avoiding me, crossing the street as I walk past.
The smell is becoming unbearable almost.
-Are your teeth clean?
What do you think about Daddy's teeth?
Oh, dear, it's now day four of not being able to brush my teeth,
and I think they're looking pretty horrible.
They certainly feel fuzzy and grim.
-Have a smell.
-Eurgh, it's stinky.
This is horrible.
Everywhere I go, I kind of feel people are looking at me funny.
More funny than normal.
OK, no sugary snacks and my teeth haven't turned black,
but they are a bit furry. To find out what's going on,
I've come to Liverpool University's dental school.
They're pioneering a new camera that reveals the damage done
by five days of neglect. Not rot, but plaque.
It's difficult to see the plaque,
because it's white on white teeth.
If you look very closely, you can see some.
I'm a bit worried about that bit. That's a bit of last night's curry.
I think that's a bit of food debris.
But if we have a look at a different image we've taken
with our special camera, which is using fluorescence now,
then we can see some really quite heavy areas of plaque.
-So this orange stuff, that's plaque?
-That's quite a lot, isn't it?
-There is really quite a lot there.
Plaque is down to those same bacteria that produce acid.
Faced with a filthy mouth, they go wild,
billions of them forming a sticky, gooey mess all over your teeth.
It won't harm your teeth like acid does,
but if you don't brush away the plaque, it eventually hardens
and this time, it's your gums that pay the price.
So this is all stuff that's taken up residence
in my mouth over the last five days. It's hooked up to the microscope
and I'm looking at this stuff, I can actually see things wriggling about.
-What's that there?
-These long, slender, cigar-shaped rods
are probably fusobacterium.
We've got probably some streptococci here,
the round-shaped bacteria.
But we've also got some of these motile bacteria,
-likely to be spirochetes.
-It's a wonder I'm still alive!
-They're like little tadpoles swimming around.
I thought I felt something in my mouth, I thought there was something odd going on!
-So, really, this is the cause of all of our problems, isn't it?
That can lead to problems with your gums,
perhaps leading on to loose teeth and eventually tooth loss.
So the moral of the story is brush your teeth, I think?
-Brush your teeth well.
-OK, so there you go.
-Jem, teeth, fillings. Any fillings?
-Two, maybe three, actually.
-My dad's a dentist, so I'm a bit embarrassed to admit this,
-but it's three. Sorry, Dad.
-No fillings. Dentally perfect.
-Oh, for goodness' sake.
More worrying than that still, your VT suggested
that brushing your teeth immediately after eating sweets
-does more harm than good.
-If you think about it,
the acid is already eroding away at the enamel.
Add a toothbrush to that, you're aggravating the problem.
Ideally, you need to wait an hour between the sweet and the brushing.
See, that makes a lot of sense.
It's kind of counterintuitive but it makes a lot of sense.
Here's something for you. What is the best food to eat, for your teeth?
-What's the one food to eat?
-A massive toothpaste sandwich.
-Which makes a lot of sense.
-Or something that neutralises the acid.
The best food you can eat for your teeth is actually cheese.
It's full of calcium and phosphorus, good minerals for your teeth.
It's also alkaline so it helps neutralise the acid,
and if you use a strong cheese, like a vintage cheddar,
it produces lots of saliva, which helps fight tooth decay.
And there's plenty more about teeth at /bang.
Just follow the links to the Open University
where you can find out how teeth evolved.
And how doctors are using fluorescence to detect disease.
Next week, Dr Yan is messing around with radioactive waste.
You may be surprised to discover
just how radioactive some things are.
And I'm off to Amarillo in Texas to investigate
a potential global shortage of helium.
You may be thinking, "So what?", but there is more to helium
-that just making your voice go squeaky.
-All interesting stuff.
I'm also going to be checking out new airport security
that you're going to have to be dealing with on your next flight.
This device finds hidden weapons through your clothes.
Interested? That's coming up next week as well as a new BBC project
called 'So You Want To Be A Scientist.'
We're looking for budding amateur researchers.
More about that next week. See you then.
Subtitles by Red Bee Media Ltd
E-mail [email protected]
Dallas downs his toothbrush to discover what causes tooth decay and gum disease, Yan explains why refreezing food is not a great idea, and Jem investigates new research that electric lights can play havoc with the way we sleep.