Sugar: One big kick in the teeth

20 November 2015

Interview with

Professor Jimmy Steele, Newcastle University and Newcastle Hospitals NHS Foundation Trust

Sugar is bad for us on many accounts but the two big effects are on our teeth andTeeth our waistlines. But why does it have this effect? How is the sweet stuff different from the other foods we eat? If we follow that journey of a chocolate bar the first place it ends up is in your mouth, coating your nashers in sugar. Professor Jimmy Steele is a dentist and told Kat Arney what happens to your teeth...

Jimmy - Well when you take that chocolate bar into your mouth and you start chewing it up, and it's delicious, it's not just you that's metabolising that chocolate bar that you're eating.  Because your mouth, of course, is full of a multitude of bacteria, different species of bacteria and much of these bacteria are actually in plaque on your teeth.  So they form that sort of sticky white material, which is really why you brush your teeth.  Your brush your teeth to get that plaque off your teeth but there are parts of your mouth, even if you are brushing really well it's very difficult to get rid of that plaque.  For example, where your teeth meet each other you just can't get our toothbrush down there. 

And so the plaque - the bacteria in the plaque - will take the sugar and will convert it into an acid, and at the sites where they do that, the ph drops and, when it hits 5.5, then the tissue of your teeth, which is actually very highly mineralised - in fact the enamel of your teeth is entirely mineral tissue - it starts to dissolve, and if that happens often enough, and frequently enough, then it starts to break down and that's what causes a cavity.

Kat - So, is this basically binge eating on sugar or is this continuous eating of sugar?  You know, I'm trying to think would it be better for me if I just had an entire bag of toffees in one go or just eat loads and loads of toffees all the time...

Jimmy - Although neither is a particularly good plan the advice I would give to you is if you really have to eat the same amount, you'd actually possibly be slightly better off if you eat it all at once, because this happens over time, so the formation of cavity actually takes really quite a long time, it's not sort of instantaneous.  So what happens is, when the sugar goes into your mouth, it goes into the plaque and the ph drops.  What then happens is saliva will tend to adjust that and take it back to a neutral ph over a period of time, maybe let's say half an hour or an hour it might come back up to normal.  But, if every thirty minutes you pop another toffee into your mouth, or a square of chocolate or whatever it is you fancy, maybe a cup of tea with spoonful sugar in it, if you do that repeatedly then the ph rarely, or never gets above 5.5, and so the period of exposure to this acidity is longer and continuous.  Now if have lots of sugar all at once, the ph will really go down, so it's bad to have a lot of  it, but it's arguably even worse if you spread it out over time and regularly take your sugar.

Kat - So you've mentioned putting sugar in your tea.  My personal vice, things like toffee and chocolate, but there's also sugar in fruits.  I did very healthily have an apple before this show.  I mean is the sugar in fruit different from the sugar that's in a chocolate bar?

Jimmy - Well, as far as your mouth is concerned, actually it is because as you heard earlier on when Ian was talking, he was talking about free sugars.  And the free sugars that are in your chocolate bar when it goes into your mouth are very, very available to the bacteria in the mouth but the sugars that still inside the cells of the apples - now some of that as you chew it might be released  - but a lot of that apple will stay as cellular form and you swallow it, and so that's actually much less damaging.  That sugar can't escape unless you mush it all out into your mouth, and so as far as your teeth are concerned, it's actually free sugars that are particularly damaging.

Kat - But you mentioned that the microbes in our mouth turn the sugar into acid, but there's also acid in fruits.  Is that the same kind of acid, is that also as damaging for our teeth?

Ian - Well it is, but it operates in a different way because a little spot of plaque if you like on your teeth  - reduces the ph at that site.  The difference with acidic drinks, for example, even very healthy things like orange juice are quite acidic, the difference with them is that they wash over your whole mouth.  So one of the classic bits of advice we give as dentists is: if you're going to have a glass of orange juice that's fantastic, it's good for you and all that but for goodness sake don't brush your teeth immediately afterwards because they may be temporarily demineralised.  Now they will remineralise very, very quickly, just with the saliva in your mouth. But if you brush your teeth just straight away when they are just a little bit soft then you may take off a little microlayer, and that's what happens.

Kat - So broadly we do hear that we're all eating more sugar, we're eating too much sugar.  Has this actually impacted on the nation's teeth.

Jimmy - Well, 50 years ago, we were in dental decay epidemic and that was really going on, I suppose, until the 70s and 80s, and since then we've actually seen a steady reduction in dental decay.  Probably one of the biggest things that happened was that fluoride went into toothpaste round about the start of the 1970s.  But a lot of other things have happened as well, we look after our mouths better, we have less decayed teeth lying around in our mouths and as they get restored the bugs in our mouth change a little bit.  So it's quite a complicated picture, but it has reduced very remarkably and, actually, in fact Britain's now a very good place from the point of view of low levels of decay when we compare ourselves to equivalent nations around the world.

Kat - Is sugar such a baddie.  If all our teeth are generally getting better, should we still be concerned and tell kids "don't eat so many sweets" and all that kind of thing?

Jimmy - So what's really happened, actually, is the prevalence, in other words the percentage of the population who are affected has reduced quite remarkably but there's still lots, and lots, and lots of people who are affected.  So, about one in three people in adults and something pretty similar in children, have at least one decayed tooth in their mouth at any given time.  So that's still quite a high percentage, and if you take the people who have some decay in their mouth, the amount of decay that they have really has not changed, certainly in the last decade if you're in that group.  So, although the size of the group's reduced, the amount of decay within the group is just as bad as it ever was and about one in seven children - from the most recent survey, which was very recent actually, published earlier this year - about one in seven children has very bad decay with infections, sepsis or multiple teeth affected.  So it's still a pretty severe condition if you've got it.

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