0:00:02 > 0:00:04Tonight, Jem takes part in an experiment
0:00:04 > 0:00:06to discover how electric light
0:00:06 > 0:00:09may be playing havoc with our sleeping patterns.
0:00:09 > 0:00:11It's morning light that is so important
0:00:11 > 0:00:12for setting the body clock.
0:00:12 > 0:00:15OK, this is it. This is truly grim.
0:00:15 > 0:00:18And Dallas downs his toothbrush
0:00:18 > 0:00:21to find out exactly what causes tooth decay and gum disease.
0:00:21 > 0:00:24- Have a smell.- Eurgh! It's stinky!
0:00:24 > 0:00:29That's Bang Goes The Theory, revealing your world with a bang.
0:00:29 > 0:00:33Electric light, something we take totally for granted.
0:00:33 > 0:00:36The flick of a switch, we get ourselves some indoor sunshine.
0:00:36 > 0:00:39But worryingly, scientists are beginning to understand
0:00:39 > 0:00:43that living under artificial light may have an unexpected effect on our bodies.
0:00:43 > 0:00:47No one really knew why until a recent discovery
0:00:47 > 0:00:49revealed a whole new way in which our eyes work.
0:00:49 > 0:00:54Our eyes are one of the best-studied organs in medical science
0:00:54 > 0:00:59yet only recently did we discover they do far more than simply see.
0:00:59 > 0:01:02Just a few years ago, researchers at Oxford University
0:01:02 > 0:01:08found that our eyes have another, subconscious response to light,
0:01:08 > 0:01:11one that deeply affects our daily lives.
0:01:11 > 0:01:14If only I could get through this impossible dark room door.
0:01:14 > 0:01:18I'm going to find out how it works from the man who discovered it,
0:01:18 > 0:01:20Professor Russell Foster.
0:01:20 > 0:01:24OK, I'm going to plunge you into darkness now.
0:01:24 > 0:01:26OK, that's pretty dark now.
0:01:26 > 0:01:29Professor Foster starts by demonstrating
0:01:29 > 0:01:31the two ways our eyes consciously see.
0:01:31 > 0:01:35These are the classic tests to find out if you're colour-blind.
0:01:35 > 0:01:38Exactly. Can you recognise any numbers in there?
0:01:38 > 0:01:42I could tell you it's black on the outside, then sort of white there,
0:01:42 > 0:01:46and this is neither black nor white, but actual colours, there's none.
0:01:46 > 0:01:49It's just shades.
0:01:49 > 0:01:52So I'm now going to increase the light a little bit.
0:01:52 > 0:01:57Now you can tell that there's like reds and browns appearing
0:01:57 > 0:02:01and then there's sort of greens and blues.
0:02:01 > 0:02:05- I'm going to go for that as a six. - The most important part of the eye
0:02:05 > 0:02:08are the light sensors or the photoreceptors.
0:02:08 > 0:02:11There's the rods, which are used for dim light vision.
0:02:11 > 0:02:14They're essentially brightness detectors.
0:02:14 > 0:02:16And then the cones, which allow us to see colour.
0:02:19 > 0:02:23In fact, there are three different types of cone in our eye.
0:02:23 > 0:02:26Each of those cones is peaking broadly in the blue part
0:02:26 > 0:02:28of the spectrum, the green part of the spectrum
0:02:28 > 0:02:32and one in the orangey red part of the spectrum.
0:02:32 > 0:02:35When you stimulate all those three receptors maximally,
0:02:35 > 0:02:40as you would with sunlight, it appears white.
0:02:40 > 0:02:44So to make artificial sunlight, surely all you need is to fool
0:02:44 > 0:02:48the eye with the right mix of red, green and blue, isn't it?
0:02:48 > 0:02:51Well, that's what we'd assumed.
0:02:53 > 0:02:56Until Professor Foster made his stunning discovery.
0:02:56 > 0:02:59A third type of light sensor in our eye.
0:02:59 > 0:03:05A colleague came across a lady who had a very strange visual defect
0:03:05 > 0:03:08whereby she'd lost all of her rod and cone cells.
0:03:08 > 0:03:11She said she had no conscious light detection but we said,
0:03:11 > 0:03:16"OK, just tell us when the lights were on and off." And quite remarkably, she could always do it.
0:03:16 > 0:03:21- Wow.- And so there's another, yet another light sensor in the eye.
0:03:21 > 0:03:25Not the rods and not the cones, but it's a group of ganglion cells.
0:03:25 > 0:03:29They have a peak in sensitivity in the blue part of the spectrum
0:03:29 > 0:03:33and it's at a colour or a wavelength which basically matches
0:03:33 > 0:03:35the blueness of a blue sky.
0:03:35 > 0:03:40These special blue sensors are nothing to do with actually seeing.
0:03:40 > 0:03:45We thought of these new receptors in the eye as body clock light sensors.
0:03:45 > 0:03:50We have an internal body clock which is constantly adjusting
0:03:50 > 0:03:52and fine-tuning every aspect of our physiology.
0:03:52 > 0:03:57So it contributes to your overall alertness, your ability to constrict your pupil,
0:03:57 > 0:04:00adjust your body clock, and probably a whole raft
0:04:00 > 0:04:02of other things we're just discovering.
0:04:02 > 0:04:06The Professor thinks these sensors evolved in our early ancestors,
0:04:06 > 0:04:09allowing them to take subconscious time cues from sunlight.
0:04:09 > 0:04:14And they worked perfectly, until engineers like me got involved.
0:04:18 > 0:04:22For millions of years, the only lights we had, really,
0:04:22 > 0:04:25were sunlight and firelight.
0:04:25 > 0:04:29But with the advent of electricity, things changed fairly dramatically.
0:04:29 > 0:04:34This electric arc actually gives off pretty good fake sunlight.
0:04:34 > 0:04:39Look, if I split up its colours. It's a very even spread on the spectrum.
0:04:39 > 0:04:44We've got red, yellow, green, blue, right the way up here.
0:04:44 > 0:04:49It's almost identical to the range of colour in natural sunlight
0:04:49 > 0:04:52with plenty of that blue that your body clock needs.
0:04:52 > 0:04:56Trouble is, it's far too bright to use at home.
0:04:56 > 0:05:02Plus, it's full of dangerous ultraviolet. Protective masks indoors? Just not a good look.
0:05:02 > 0:05:05So I'll move on swiftly, just like mankind did,
0:05:05 > 0:05:08to this, the incandescent bulb, the kind of standard lightbulb.
0:05:08 > 0:05:12Electricity can make a thin wire very hot
0:05:12 > 0:05:17and at a few thousand degrees, it'll start to glow white hot.
0:05:17 > 0:05:21But this is no ordinary wire, this is tungsten wire,
0:05:21 > 0:05:24which melts at well over 3,000 degrees Celsius.
0:05:24 > 0:05:26I have to put a glass over the top of it,
0:05:26 > 0:05:30and suck the air out of it, so that wire doesn't burn when it gets hot.
0:05:33 > 0:05:36There you go. It's now sat in a vacuum.
0:05:39 > 0:05:46There we go. That is a lightbulb. It's like a miniature star in a jar.
0:05:46 > 0:05:51Although this looks like sunlight, the mix of colours is not the same.
0:05:51 > 0:05:53It has less in the way of blue and violet in it
0:05:53 > 0:05:57than maybe bright daylight would have, so in light like this,
0:05:57 > 0:06:00there's less of the colour those sky blue sensors respond to.
0:06:00 > 0:06:05But traditional bulbs like this are too inefficient for moderate use.
0:06:05 > 0:06:09Making artificial light through extreme temperatures,
0:06:09 > 0:06:14it requires a relatively large amount of power for not that much light.
0:06:14 > 0:06:17So in our energy efficient modern age,
0:06:17 > 0:06:20we've moved towards lamps that operate
0:06:20 > 0:06:22from an entirely different phenomenon.
0:06:22 > 0:06:26Fluorescent lights work a bit like the Northern Lights,
0:06:26 > 0:06:30where electrical energy gives the sky an eerie glow.
0:06:30 > 0:06:34I'm pumping the air out of this tube to recreate the upper atmosphere.
0:06:34 > 0:06:39A blast of a few thousand volts should make that low pressure air
0:06:39 > 0:06:41produce an almost magical effect.
0:06:43 > 0:06:48Look at that. I mean, it's a weird, pink light,
0:06:48 > 0:06:52as you may expect from a kind of home-made aurora.
0:06:52 > 0:06:56Of course, it's not magic. It's atomic emission of pure cold light.
0:06:56 > 0:07:01I'm pretty chuffed with it. Though it's not much like sunlight yet,
0:07:01 > 0:07:05but I can fix that. How do you go from that beautiful pink
0:07:05 > 0:07:07to the classic white fluorescent we're used to?
0:07:07 > 0:07:12Well, what you have to do is coat the inside of the tube with a powder,
0:07:12 > 0:07:16a mix of chemicals called phosphors
0:07:16 > 0:07:18that gives off a whole range of colours
0:07:18 > 0:07:23when stimulated by the UV light that's also given off by those atoms.
0:07:23 > 0:07:25Let's see how this goes.
0:07:28 > 0:07:30Oh!
0:07:30 > 0:07:33It's a pretty white light.
0:07:33 > 0:07:35All strip lights work like this,
0:07:35 > 0:07:38and it's what's coiled up inside low-energy bulbs.
0:07:38 > 0:07:41It's still made up of different colours, but this time,
0:07:41 > 0:07:45instead of it being a smooth spectrum from red to violet,
0:07:45 > 0:07:48instead it's distinct bands of colour.
0:07:48 > 0:07:52The different bands are produced by different glowing powders.
0:07:52 > 0:07:55Now, you only need a few bands to trick the eye into seeing white,
0:07:55 > 0:07:58but unless the right sky blue is there,
0:07:58 > 0:08:03there's nothing for those newly discovered receptors.
0:08:03 > 0:08:06Our modern lives are a jumble of different artificial lights
0:08:06 > 0:08:09and it could be playing havoc with our body clock.
0:08:09 > 0:08:12I'm going to do a little experiment and I think it's a world first.
0:08:12 > 0:08:15I'm going to see how much of that blue light
0:08:15 > 0:08:20I'm exposed to over a typical 24 hours and when.
0:08:20 > 0:08:22Which means carrying this kit around with me
0:08:22 > 0:08:25to analyse the spectrum wherever I go.
0:08:43 > 0:08:46I'm hoping Professor Foster can tell me what all this
0:08:46 > 0:08:49might mean for my body.
0:08:49 > 0:08:53OK, Jem, so what we've looked at here is the amount of light
0:08:53 > 0:08:55in the blue, the blue skylight at 480 nanometres.
0:08:55 > 0:09:00- OK.- It's very clear that you went outside just after nine o'clock
0:09:00 > 0:09:02and the light levels have just rocketed.
0:09:02 > 0:09:05- They've gone absolutely huge. - I cycle to work.
0:09:05 > 0:09:10It takes about half an hour. This day, I had to pop out and do a bunch of other stuff as well.
0:09:10 > 0:09:13And that's really important, because it's morning light
0:09:13 > 0:09:17that's so important for setting the body clock. So, wittingly or not,
0:09:17 > 0:09:20you've seen light during the most important part of the day.
0:09:20 > 0:09:23So in the winter, when you're kind of going to work and it's dark
0:09:23 > 0:09:27and it's just getting light as you go into work quite often,
0:09:27 > 0:09:29are you effectively giving yourself jetlag?
0:09:29 > 0:09:31Your body's not sure what time of day it is.
0:09:31 > 0:09:34There's increasing evidence that's exactly what we're doing.
0:09:34 > 0:09:38I think there's an opportunity here. In the underground,
0:09:38 > 0:09:40in the tubes, we could have augmented lighting,
0:09:40 > 0:09:44we could actually try and provide a brighter morning light environment,
0:09:44 > 0:09:49- which would help stabilise internal time.- Anything that makes travelling
0:09:49 > 0:09:53on the tube slightly better for you is a good thing.
0:09:53 > 0:09:55During the day, I'm only getting bursts
0:09:55 > 0:09:58of that all-important blue light when I go outdoors.
0:09:58 > 0:10:02So what's the deal with the artificial lights I'm using?
0:10:02 > 0:10:05- Here I am in the workshop. - Oh, my goodness.
0:10:05 > 0:10:08This has got to be fluorescent light. You can tell that
0:10:08 > 0:10:13because of these sharp emission spectra in the blue,
0:10:13 > 0:10:17the green and the red, but you've got very little blue.
0:10:17 > 0:10:22So not only is it low, but it's actually lacking in blue light, which is what you want.
0:10:22 > 0:10:28Is there an effect on me of having such low light levels at work?
0:10:28 > 0:10:31The loss of blue light would have a distinct effect
0:10:31 > 0:10:33on your levels of alertness.
0:10:33 > 0:10:37Fluorescent lights give off very distinctive colours.
0:10:37 > 0:10:41- But they're not the only lights in my life.- So what time of day?
0:10:41 > 0:10:45- This is midday.- It's strange, because it's not fluorescent light,
0:10:45 > 0:10:49cos there's no great big peaks. Is this a computer screen perhaps?
0:10:49 > 0:10:53It's like talking to Derren Brown.
0:10:53 > 0:10:55Yes, that probably is a computer screen.
0:10:55 > 0:10:57You've got a nice blue enrichment there,
0:10:57 > 0:11:00which means that if you were looking at a computer screen like this
0:11:00 > 0:11:04at night, before you're going to bed, that blue enrichment
0:11:04 > 0:11:07could actually increase alertness and so significantly delay
0:11:07 > 0:11:10your tendency to fall asleep and go to bed.
0:11:10 > 0:11:14My lights at home are different again. Can he identify those?
0:11:14 > 0:11:18You don't have any big peaks in it, so it's not fluorescent light.
0:11:18 > 0:11:21But it could be something like a halogen light,
0:11:21 > 0:11:23and so you see the broad tungsten light,
0:11:23 > 0:11:26relatively enriched in the red compared to the blue.
0:11:26 > 0:11:29- You've got those little halogen lights?- Yes, I have.
0:11:29 > 0:11:33So if I wanted lighting in my home to make me feel alert,
0:11:33 > 0:11:36or at work, to make me feel alert, I'd be looking to have
0:11:36 > 0:11:40lighting that had a high enough proportion, and a high enough
0:11:40 > 0:11:44intensity of this blue, but then I wouldn't want too much of that
0:11:44 > 0:11:47in the evening, otherwise I'd stay alert when I wanted to go to sleep.
0:11:47 > 0:11:50Exactly. And this represents a huge problem
0:11:50 > 0:11:52for people who don't get out very much.
0:11:52 > 0:11:55If you're in a nursing home, with relatively dim light,
0:11:55 > 0:11:58you'll never get that bright exposure and the body clock
0:11:58 > 0:12:02will tend to drift through time. And also the various rhythms,
0:12:02 > 0:12:06so the rhythms that regulate your gut function or your brain function
0:12:06 > 0:12:11or your liver function will then start to drift apart slowly,
0:12:11 > 0:12:13and so you won't have very fine-tuned
0:12:13 > 0:12:17and well ordered physiology under those circumstances.
0:12:17 > 0:12:21I think that is a really, really interesting film.
0:12:21 > 0:12:25Off the back of that, there's obvious things you can do to help.
0:12:25 > 0:12:29Don't be looking at your computer before you go to sleep,
0:12:29 > 0:12:32and if you can, in the morning, go out and get a bit of sunshine.
0:12:32 > 0:12:37It makes sense. But armed with that knowledge, presumably we can start to develop
0:12:37 > 0:12:40technologies that are geared to how we've actually evolved,
0:12:40 > 0:12:43because clearly, as a species, we're not evolved to live
0:12:43 > 0:12:48- in the world we've created for ourselves.- You're bang on the money.
0:12:48 > 0:12:51There are companies out there at the moment that are actually
0:12:51 > 0:12:54developing artificial lights that change their spectra during the day
0:12:54 > 0:12:56to sort of match what daylight does.
0:12:56 > 0:12:59My view, though, no substitute for daylight.
0:12:59 > 0:13:03Although our eyes adjust brilliantly to different light levels,
0:13:03 > 0:13:06it can actually be thousands of times brighter outside
0:13:06 > 0:13:08- than under domestic lights. - You can't beat the sun.
0:13:08 > 0:13:12But in a country like this with pretty grim winters,
0:13:12 > 0:13:15anything you could do to help you feel better is a good thing.
0:13:15 > 0:13:19For example, I do feel really rubbish in the winter,
0:13:19 > 0:13:22so I bought a seasonal affective disorder lamps, you know those?
0:13:22 > 0:13:26But after watching your film, I've realised why I was disappointed.
0:13:26 > 0:13:28I was using them in the evening after college,
0:13:28 > 0:13:31from seven to 11 o'clock or something,
0:13:31 > 0:13:34and now I know to have used them in the morning
0:13:34 > 0:13:36to actually kick off my body clock, yeah?
0:13:36 > 0:13:40Exactly. The strong morning light makes the biggest difference.
0:13:40 > 0:13:42- And coffee.- And coffee. - Very important.
0:13:42 > 0:13:45Interesting stuff there. Next up, it's Dr Yan.
0:13:45 > 0:13:48He's in the kitchen this week talking about refreezing.
0:13:48 > 0:13:51We've all been there. You take out a frozen chicken dinner
0:13:51 > 0:13:54and you don't eat all of it but you know not to refreeze it.
0:13:54 > 0:13:58But do you know exactly why that is? Dr Yan is about to explain all.
0:14:00 > 0:14:04Using six chicken breasts, a punnet of strawberries and some fresh carrots,
0:14:04 > 0:14:07I'm going to get to the bottom of this domestic dilemma.
0:14:07 > 0:14:11These two, I'm going to put straight back in the fridge.
0:14:11 > 0:14:13These two I'm going to leave on the side. But these, well,
0:14:13 > 0:14:17I'm going to put them in the freezer now but I'm going to defrost them
0:14:17 > 0:14:20and refreeze them every day for the next five days.
0:14:20 > 0:14:23The carrots and strawberries I'm going to put in the freezer, too.
0:14:23 > 0:14:29That's not the normal place for this stuff but it'll all become clear.
0:14:29 > 0:14:31Now all I need to do is wait.
0:14:36 > 0:14:38Right, this should be done now.
0:14:38 > 0:14:42We all know that water turns solid when it freezes.
0:14:42 > 0:14:44It forms rigid crystals of ice.
0:14:44 > 0:14:48Well, 75% of this chicken breast and in fact, 90% of these,
0:14:48 > 0:14:52actually is water, so these are basically just solid blocks of ice,
0:14:52 > 0:14:56and ice crystals can be nasty things if you're a carrot.
0:14:56 > 0:14:59Food like this is made up of individual cells.
0:14:59 > 0:15:01Imagine them as tiny balloons filled with water.
0:15:01 > 0:15:05When they're not frozen, they keep the carrot nice and crunchy,
0:15:05 > 0:15:09but that all changes when the cells begin to freeze.
0:15:09 > 0:15:13Now, ice crystals inside the carrot act like microscopic needles,
0:15:13 > 0:15:15puncturing the cells.
0:15:20 > 0:15:22While it's frozen, you don't notice any difference,
0:15:22 > 0:15:25but as it defrosts, the water all oozes out.
0:15:29 > 0:15:32Which leaves the cells saggy and empty
0:15:32 > 0:15:36and us with a floppy, leaky carrot. Eurgh.
0:15:36 > 0:15:40And the strawberries, well, they're even worse. Look.
0:15:40 > 0:15:44The effect on meat is not nearly so severe
0:15:44 > 0:15:47but the same principle applies. But that's just it.
0:15:47 > 0:15:50It's only physical damage. Not very nice to eat, maybe,
0:15:50 > 0:15:54but totally harmless. There is something else
0:15:54 > 0:15:57we need to worry about, though. Bacteria.
0:15:57 > 0:16:01We all know that harmful bacteria on food can give you a dodgy tummy.
0:16:01 > 0:16:04On something like this, you could easily expect there to be
0:16:04 > 0:16:0710,000 bacteria per square centimetre.
0:16:07 > 0:16:10But under the right conditions, bacteria can quickly multiply
0:16:10 > 0:16:14to 10 or even 100 million per square centimetre,
0:16:14 > 0:16:18and that's when they're likely to make you ill. So does freezing,
0:16:18 > 0:16:22thawing and refreezing chicken make the bacteria any more harmful
0:16:22 > 0:16:25than just leaving them in the fridge or out on the side?
0:16:25 > 0:16:31Here we go. Every morning for five days, I'm going to take the chicken
0:16:31 > 0:16:34out of the freezer to defrost and every night put it back in again
0:16:34 > 0:16:39to refreeze. Then, I'm sending my refrozen chicken breast,
0:16:39 > 0:16:41along with the one I left in the fridge
0:16:41 > 0:16:45and the one that's been at room temperature the whole time, to be tested at a lab.
0:16:45 > 0:16:47Fantastic.
0:16:47 > 0:16:48Now, here are the results.
0:16:48 > 0:16:51The lab wouldn't actually send me back the samples
0:16:51 > 0:16:55because they were so contaminated, but this is what they found.
0:16:55 > 0:16:58Any coloured spots you see are harmful coliform bacteria.
0:16:58 > 0:17:02These are the results from the fridge chicken. There's not that many spots.
0:17:02 > 0:17:04There's a pair there and another two spots there
0:17:04 > 0:17:08but, you know, that's not that many. I'd probably eat that one.
0:17:08 > 0:17:11Here are the results from the chicken left out on the side.
0:17:11 > 0:17:15Loads of bacteria. The blue one is E.Coli. You've probably heard of it.
0:17:15 > 0:17:19You don't want to be eating lots of those. They thrive in a danger zone
0:17:19 > 0:17:23between five and 55 degrees Celsius.
0:17:23 > 0:17:27Now for the moment of truth. My refrozen chicken.
0:17:27 > 0:17:30Whoa, look at that, there's loads of coloured dots.
0:17:30 > 0:17:33There's fewer red ones than in the chicken left out on the side
0:17:33 > 0:17:36but there are three E.Coli there and, together with the others,
0:17:36 > 0:17:40enough to make you ill. The temperature's made the difference.
0:17:40 > 0:17:43Every time this chicken was defrosted, parts of it
0:17:43 > 0:17:46entered that temperature danger zone, from the first few minutes.
0:17:46 > 0:17:50And they stayed there until the chicken was put back in the freezer
0:17:50 > 0:17:54many hours later, allowing the bacteria to multiply the whole time.
0:17:55 > 0:17:59So it's not the freezing or refreezing that's the problem,
0:17:59 > 0:18:02it's the time the bacteria spend in the danger zone
0:18:02 > 0:18:05while the food defrosts. And it's not just raw meat, either.
0:18:05 > 0:18:08The same applies to re-freezing old cooked food.
0:18:08 > 0:18:11The bacteria will still be there lying in wait.
0:18:11 > 0:18:15I've just noticed a really interesting phenomenon.
0:18:15 > 0:18:18Dr Yan, he's done a few experiments in kitchens
0:18:18 > 0:18:22over the last few years, and every time, he's in a different kitchen.
0:18:22 > 0:18:27- Not only is he a brilliant scientist, he's also a property magnate.- Nothing would surprise me about Dr Yan.
0:18:27 > 0:18:31What I didn't quite get, surely with all those bacteria,
0:18:31 > 0:18:34once you cook it, get it to a couple of hundred degrees,
0:18:34 > 0:18:37- it kills the bacteria anyway? - The heat does kill them
0:18:37 > 0:18:40but it's not the bacteria themselves that cause illness,
0:18:40 > 0:18:45it's the toxins they release as they're metabolising in your body.
0:18:45 > 0:18:49So, for example, nasty E.Coli. You can kill the actual bacteria
0:18:49 > 0:18:55in the heat of the food, and you can break down some of the toxins that it produces, but not all of them,
0:18:55 > 0:18:59- and it's the remaining toxins that make you ill.- Interesting.
0:18:59 > 0:19:02We're going to stay on the Dr Yan lovefest theme.
0:19:02 > 0:19:06Here is his weekly brainteaser. What is this?
0:19:06 > 0:19:10- The moon on a piece of paper.- Not the actual moon, a picture of it.
0:19:10 > 0:19:13Very bright. That's not actually the conundrum.
0:19:13 > 0:19:18How many times would I have to fold this piece of paper in equal parts
0:19:18 > 0:19:21in order for it to be able to reach that moon 250,000 miles above me?
0:19:21 > 0:19:24That's maybe 0.1mm thick. You are looking at thousands
0:19:24 > 0:19:28of trillions of times thicker. I don't even think you could do it.
0:19:28 > 0:19:33It's fewer than you think because actually, it's an exponential.
0:19:33 > 0:19:38Cryptic clue. The answer's actually the answer to the ultimate question.
0:19:38 > 0:19:42If that's confused your brain like it has mine, don't worry,
0:19:42 > 0:19:46Dr Yan explains it perfectly well on our website, as always, /bang.
0:19:46 > 0:19:49OK, coming up next, it's oral hygiene.
0:19:49 > 0:19:51Now, like most people, I brush my teeth twice a day
0:19:51 > 0:19:54to avoid getting fillings, but it turns out
0:19:54 > 0:19:58that the main cause of tooth decay isn't due to lack of brushing.
0:19:58 > 0:20:01And if you don't believe me, I've got 2,000 years of evidence to prove it.
0:20:01 > 0:20:07Meet my three new friends, all former London residents.
0:20:07 > 0:20:10This is a female Roman skull and if you look at the teeth,
0:20:10 > 0:20:13there's a bit of wear and tear, but no tooth decay at all.
0:20:13 > 0:20:17Surprisingly, very good condition. Fast forward to a mediaeval skull
0:20:17 > 0:20:21and despite the lack of electric toothbrushes at the time,
0:20:21 > 0:20:23again, very good teeth, no sign of any decay.
0:20:23 > 0:20:27Cut to a post-mediaeval skull, and it's not pretty.
0:20:27 > 0:20:32You can see here, very bad tooth decay. An abscess here.
0:20:32 > 0:20:36It's not looking good. But why is that? One word, sugar.
0:20:36 > 0:20:39This person's generation was the first in history
0:20:39 > 0:20:43that could easily get hold of it, and they loved it.
0:20:43 > 0:20:46And although they were probably no worse at brushing,
0:20:46 > 0:20:50the sweet tooth alone was enough to set in the rot.
0:20:50 > 0:20:53Allow me to demonstrate with this tooth-shaped cake.
0:20:53 > 0:20:56When you eat something delicious and sugary like this,
0:20:56 > 0:20:58it's not just you that gets a treat,
0:20:58 > 0:21:01because inside our mouth, it's full of bacteria.
0:21:01 > 0:21:04Most of the time, it's harmless and causes us no trouble.
0:21:04 > 0:21:08Until, that is, you decide to eat or drink something sugary.
0:21:08 > 0:21:12The bacteria thrive on sugar and as they digest it,
0:21:12 > 0:21:14they create acid as a by-product.
0:21:14 > 0:21:18It's this acid that is the problem because as it bathes the teeth,
0:21:18 > 0:21:20it starts to dissolve the enamel.
0:21:20 > 0:21:23This process is called demineralisation
0:21:23 > 0:21:26and it happens every time you eat or drink something sugary.
0:21:28 > 0:21:31Enamel is actually one of the strongest parts of the body,
0:21:31 > 0:21:36but under attack from acid, mineral ions are removed
0:21:36 > 0:21:39and that lattice structure is weakened.
0:21:39 > 0:21:42If it continues to come into contact with acid,
0:21:42 > 0:21:46eventually it'll collapse and that's when you get a cavity.
0:21:47 > 0:21:49The acid gets to work in minutes.
0:21:49 > 0:21:52Brushing at night can't undo the damage,
0:21:52 > 0:21:56while brushing straightaway can even make it worse.
0:21:56 > 0:21:59Thankfully for us, we have a natural weapon against tooth decay.
0:21:59 > 0:22:02It's called saliva and it helps to neutralise
0:22:02 > 0:22:06and wash away that acid, but it also contains mineral ions,
0:22:06 > 0:22:10replacing the ones that are lost through acid erosion,
0:22:10 > 0:22:12remineralising and helping strengthen
0:22:12 > 0:22:16that latticework structure of the teeth.
0:22:16 > 0:22:18But if you keep on eating sugary snacks,
0:22:18 > 0:22:21your saliva can't keep up with the repair work.
0:22:21 > 0:22:24What starts as a small cavity gets deeper and deeper.
0:22:24 > 0:22:28And if the cavity expands and reaches the inner,
0:22:28 > 0:22:30living part of the tooth, the dentine,
0:22:30 > 0:22:34it's going to get painful because that's where your nerves are.
0:22:34 > 0:22:37Most of us at this point are going to consider a trip
0:22:37 > 0:22:40to the dentist, but if left unchecked, you're going to get
0:22:40 > 0:22:45full-blown tooth decay and, eventually, your tooth will fall out.
0:22:45 > 0:22:49The best way to avoid decay, then, is to avoid sugar.
0:22:49 > 0:22:52So what's with all the brushing?
0:22:52 > 0:22:56I'm going to find out by hanging up my toothbrush for five days.
0:22:56 > 0:22:59OK, this is it. This is truly grim.
0:22:59 > 0:23:02This is the last time I'm going to brush my teeth
0:23:02 > 0:23:06for the next five days, so don't come anywhere near me.
0:23:06 > 0:23:10It's day three. This is the third day I haven't brushed my teeth
0:23:10 > 0:23:14and people are avoiding me, crossing the street as I walk past.
0:23:14 > 0:23:18The smell is becoming unbearable almost.
0:23:18 > 0:23:20- Are your teeth clean? - Yeah.- Let's see.
0:23:20 > 0:23:23What do you think about Daddy's teeth?
0:23:25 > 0:23:27Yucky.
0:23:27 > 0:23:32Oh, dear, it's now day four of not being able to brush my teeth,
0:23:32 > 0:23:35and I think they're looking pretty horrible.
0:23:35 > 0:23:38They certainly feel fuzzy and grim.
0:23:38 > 0:23:41- Have a smell.- Eurgh, it's stinky.
0:23:41 > 0:23:44This is horrible.
0:23:44 > 0:23:49Everywhere I go, I kind of feel people are looking at me funny.
0:23:49 > 0:23:51More funny than normal.
0:23:54 > 0:23:58OK, no sugary snacks and my teeth haven't turned black,
0:23:58 > 0:24:02but they are a bit furry. To find out what's going on,
0:24:02 > 0:24:06I've come to Liverpool University's dental school.
0:24:06 > 0:24:11They're pioneering a new camera that reveals the damage done
0:24:11 > 0:24:14by five days of neglect. Not rot, but plaque.
0:24:14 > 0:24:18It's difficult to see the plaque,
0:24:18 > 0:24:20because it's white on white teeth.
0:24:20 > 0:24:22If you look very closely, you can see some.
0:24:22 > 0:24:26I'm a bit worried about that bit. That's a bit of last night's curry.
0:24:26 > 0:24:29I think that's a bit of food debris.
0:24:29 > 0:24:32But if we have a look at a different image we've taken
0:24:32 > 0:24:37with our special camera, which is using fluorescence now,
0:24:37 > 0:24:42then we can see some really quite heavy areas of plaque.
0:24:42 > 0:24:45- So this orange stuff, that's plaque?- That's plaque.
0:24:45 > 0:24:48- That's quite a lot, isn't it? - There is really quite a lot there.
0:24:48 > 0:24:52Plaque is down to those same bacteria that produce acid.
0:24:52 > 0:24:55Faced with a filthy mouth, they go wild,
0:24:55 > 0:24:59billions of them forming a sticky, gooey mess all over your teeth.
0:24:59 > 0:25:02It won't harm your teeth like acid does,
0:25:02 > 0:25:05but if you don't brush away the plaque, it eventually hardens
0:25:05 > 0:25:08and this time, it's your gums that pay the price.
0:25:10 > 0:25:12So this is all stuff that's taken up residence
0:25:12 > 0:25:16in my mouth over the last five days. It's hooked up to the microscope
0:25:16 > 0:25:20and I'm looking at this stuff, I can actually see things wriggling about.
0:25:20 > 0:25:24- What's that there?- These long, slender, cigar-shaped rods
0:25:24 > 0:25:27are probably fusobacterium.
0:25:27 > 0:25:30We've got probably some streptococci here,
0:25:30 > 0:25:33the round-shaped bacteria.
0:25:33 > 0:25:37But we've also got some of these motile bacteria,
0:25:37 > 0:25:42- likely to be spirochetes. - It's a wonder I'm still alive!
0:25:42 > 0:25:45- They're like little tadpoles swimming around.- They are.
0:25:45 > 0:25:50I thought I felt something in my mouth, I thought there was something odd going on!
0:25:50 > 0:25:54- So, really, this is the cause of all of our problems, isn't it?- It is.
0:25:54 > 0:25:56That can lead to problems with your gums,
0:25:56 > 0:26:01perhaps leading on to loose teeth and eventually tooth loss.
0:26:01 > 0:26:03So the moral of the story is brush your teeth, I think?
0:26:03 > 0:26:06- Brush your teeth well. - OK, so there you go.
0:26:06 > 0:26:11- Jem, teeth, fillings. Any fillings? - Two, maybe three, actually.
0:26:11 > 0:26:14- Liz?- My dad's a dentist, so I'm a bit embarrassed to admit this,
0:26:14 > 0:26:18- but it's three. Sorry, Dad. - No fillings. Dentally perfect.
0:26:18 > 0:26:20- Oh, for goodness' sake.- Actually...
0:26:20 > 0:26:24More worrying than that still, your VT suggested
0:26:24 > 0:26:28that brushing your teeth immediately after eating sweets
0:26:28 > 0:26:30- does more harm than good. - If you think about it,
0:26:30 > 0:26:34the acid is already eroding away at the enamel.
0:26:34 > 0:26:37Add a toothbrush to that, you're aggravating the problem.
0:26:37 > 0:26:41Ideally, you need to wait an hour between the sweet and the brushing.
0:26:41 > 0:26:42See, that makes a lot of sense.
0:26:42 > 0:26:45It's kind of counterintuitive but it makes a lot of sense.
0:26:45 > 0:26:49Here's something for you. What is the best food to eat, for your teeth?
0:26:49 > 0:26:53- What's the one food to eat? - A massive toothpaste sandwich.
0:26:53 > 0:26:57- Which makes a lot of sense.- Or something that neutralises the acid.
0:26:57 > 0:27:00The best food you can eat for your teeth is actually cheese.
0:27:00 > 0:27:05It's full of calcium and phosphorus, good minerals for your teeth.
0:27:05 > 0:27:07It's also alkaline so it helps neutralise the acid,
0:27:07 > 0:27:10and if you use a strong cheese, like a vintage cheddar,
0:27:10 > 0:27:13it produces lots of saliva, which helps fight tooth decay.
0:27:13 > 0:27:16And there's plenty more about teeth at /bang.
0:27:16 > 0:27:19Just follow the links to the Open University
0:27:19 > 0:27:22where you can find out how teeth evolved.
0:27:22 > 0:27:27And how doctors are using fluorescence to detect disease.
0:27:27 > 0:27:31Next week, Dr Yan is messing around with radioactive waste.
0:27:31 > 0:27:33You may be surprised to discover
0:27:33 > 0:27:35just how radioactive some things are.
0:27:35 > 0:27:38And I'm off to Amarillo in Texas to investigate
0:27:38 > 0:27:41a potential global shortage of helium.
0:27:41 > 0:27:44You may be thinking, "So what?", but there is more to helium
0:27:44 > 0:27:47- that just making your voice go squeaky.- All interesting stuff.
0:27:47 > 0:27:50I'm also going to be checking out new airport security
0:27:50 > 0:27:54that you're going to have to be dealing with on your next flight.
0:27:54 > 0:27:57This device finds hidden weapons through your clothes.
0:27:57 > 0:28:02Interested? That's coming up next week as well as a new BBC project
0:28:02 > 0:28:04called 'So You Want To Be A Scientist.'
0:28:04 > 0:28:07We're looking for budding amateur researchers.
0:28:07 > 0:28:09More about that next week. See you then.
0:28:09 > 0:28:11- Bye-bye.- Bye-bye.- Take care.
0:28:14 > 0:28:18Subtitles by Red Bee Media Ltd
0:28:18 > 0:28:21E-mail subtitling@bbc.co.uk