'Sugar-ally sticks!' One of the old ladies has made a discovery and they all crowd round, clucking. We're in Glasgow's East End, and on the counter of Glickman's sweetie shop, beside the packets of sweet tobacco (cocoa and sugar-coated coconut), is a stack of brittle black liquorice sticks. The ladies each pick up a sugar-ally stick and a chorus breaks out:

Sugar ally water

Black as lum!

Gather up your pennies

You can all have some!

You make sugar-ally water, I'm told, by crumbling the sticks into a jug with a glass of hot water. Then you put it under your bed and leave it overnight. In the morning you've got a sweet liquorice water drink. 'You see, there was not these commercial soda drinks then,' says Netta Thomson. 'You'd never have a treat as good as sugar-ally water.' 'Well,' says 86-year-old Rena McNeil, looking dubious, 'there was alphabet cachous'. 'And aniseed balls,' says Irene Creighton. 'And sherbert straws,' says Stella Telford. 'Treacle toffees!', 'dolly mixture!', 'liquorice comfits!', 'soor plums!', 'lemonade rock!', 'lucky potatoes!' 'Oh, you were so posh! We called them lucky tatties!'

You suspect that the which-sweetie's-best argument hasn't changed much since Rena and her friends were in the playground at nearby Charlotte Street school seven decades ago. Glickman's Pure Confectionery has, since 1903, been the place where the children of Glasgow Cross came to spend their pocket money. The shop looks alien now, with its glittering shopfront full of highly coloured candy, standing in a sad row of prematurely shuttered small businesses, a failed property development - 'Future Homes!' - across the road. Glickman's is a throwback to a time when sweets came out of jars in paper bags, the letter K - as in kola kubes - was cool, and the consumption of sugar was pure, un-guilty pleasure.

Netta Thomson stops the litany of sweetie-naming. 'I'm not talking about sweets, I'm talking about the sodas,' she says, a little crossly. 'You'd get nothing as good as sugar-ally water.' 'Well, we'd get a small bottle of American cream soda,' says Irene. 'Between us, that would last a week. Five people. Nowadays, these bairns get a Coke each, every day.' 'Aye, and sweeties in their lunch box'. 'I'd get a halfpenny from my Dad on Friday, pay-day,' says Rena. What would she buy? 'A small bar of Cadbury's milk chocolate,' she says dreamily - 'Or buttermilk dainties. Mind you, that was before the war.' 'During the war,' says Irene, 'my mother would take a square of chocolate, and quarter it, a bit for each of us.'

'Anyway,' says Rena briskly, 'can't stop here gabbing. I've got my shopping to do.' With a flash of off-white dentures the ladies smile their goodbyes over the counter to Julie Birkett, great grand-daughter of the Isaac Glickman who founded the shop. They head off into the thin Glasgow sunshine, still talking, high on sugar and nostalgia.

Glickman's sits on the edge of Glasgow's Calton district, once a proud working-class neighbourhood that thrived in Glasgow's boom years in the 19th and early 20th century. Sweets helped Glasgow become the industrial giant it was. Sugar from the West Indies colonies came on ships built in the Clyde to be processed in refineries beside the river - and cheap, easily available sugar is the historical key to the Scots amazing sweets and sugared-drinks habit. The Calton is sad now, no longer famous for anything except as the place in the UK with the lowest life expectancy (53.9 years, which is seven years less than male life expectancy is in Iraq) and sugar is certainly not the most lethal of the addictions that shorten the lives of the people there. Yet it is of enormous concern to Scotland's health agencies. The grim statistics on obesity and tooth decay are a huge embarrassment - they are the unarguable evidence of ingrained poverty and poor education in a country that prides itself on the standard of its schools and its newly devolved prosperity.

And the statistics are shaming. Scottish children consume more fizzy drinks than anyone else in Europe and they have the worst teeth in Britain - with an average 'd3mft' count (that's the average number of decayed, missing or filled teeth) of 2.36 at five years old, rising to over three in Glasgow. (In England generally the d3mft figure is 1.47, and less than one in places like Surrey and Sussex). Almost half of all Scottish five year olds suffer from tooth decay and a Glaswegian 12-year-old has teeth similar - according to the World Health Organisation - to those of a 12-year-old in Kazakhastan or Cambodia. Glaswegians aren't ignorant of the problem - they've long called lemonade and chips 'the Glesca diet'. It's a city that's learned to laugh at its adversities.

The Scottish Executive has declared the people's teeth 'unacceptable'. A 2004 Executive consultation document states: 'Scotland's children still have too many diseased teeth. Dental disease still results in extreme pain and discomfort, infection, social embarrassment and interrupted work and education for a significant part of the Scottish population.' Over the next two years, £26 million will be spent in Scotland on oral-health education for children, on free packs of toothbrush and toothpaste in primary schools. There is more cash to address the quality of school food, and to provide free fruit in deprived areas. The sale of fizzy drinks in schools will be banned by next year - which makes sense, since most of the sugar modern children get is not from sweets but from drinks, with the average 330ml can containing 25-30g of sugar.

The sugar content in soft drinks is one of the junk food industry's great dirty statistics - even 'healthy' apple or blackcurrant juices like Sainsbury's Blue Parrot Café range can contain as much as 14mg of sugar per 100ml. The blackcurrant Ribena that we all happily glugged on as children - 'because it's good for you' - has more sugar in it (34.56g, or seven teaspoons, in the modern 288ml carton) than does Coca-Cola. The fact that Ribena's parent, Glaxo Smith Kline, also sells 600 million tubes of toothpaste a year, is one of mega-industry's charming ironies.

But one Edinburgh NHS children's dentist told me that she thinks the efforts to change Scottish diets have now been proven just about useless. 'It's clear now that education just hasn't worked.' This is echoed by the social policy researcher Peter Marsh, who says: 'The people responsible for selling health messages have a fundamental lack of understanding about what motivates children and adolescents. You don't condition out these preferences by restriction - you just increase the preference. As a parent I know that banning foods doesn't work - the only thing that does is increasing the variety of foods that's on offer.' For the dentist - who won't be named - the only governmental effort that could make a real difference would be putting fluoride in Scottish drinking water. This was rejected in Scotland in the Seventies, when many English cities began doing it, and again two years ago, both times on the grounds that universal application of fluoride infringed the right to choose. Scots children have bled for that bit of whimsy ever since, and it's been pretty painful for the taxpayer, too.

Things are slowly improving. Scottish teeth were so bad a generation ago that a lot of people just decided they'd be better off without them - 'A girl,' the Edinburgh dentist says, 'would often have all her teeth pulled when she was 18, and get a nice set of dentures, so as not to be a trouble to her husband when she married.' This may sound like legend, but it's a fact that in 1972 an amazing 44% of Scots over 16 had no teeth at all.

Even today the Scots are fairly toothless - one in six Scots women and one in seven men have lost all their teeth by their mid-50s. But, for at least a decade, Scots' teeth have been improving - even though sugar consumption is up, massively. According to the Scottish Health Education Board a child in a deprived area now eats '60 teaspoons', or 300g of sugar, every day. The intake is even higher if you add in all the hidden sugars, according to research carried out by the nutritionist Maisie Steven for her book The Good Scots Diet. She calculates the average active schoolchild's intake at 425g - of which sweets make up just 90g, and drinks 125g. This is remarkable enough - but Smith says that's four times the sugar intake of Scots children in 1939, and nearly double what it was in 1982.

And, though the blame link between sugar and fat is less simple than that between sugar and bad teeth, the Scots waddle ahead of all the United Kingdom when it comes to being overweight. According to NHS statistics, one in five 12 year-olds is obese and one in three is overweight; two-thirds of adult men are said to be overweight or obese (though here we get into hotly disputed areas as to what levels of 'overweight' are actually dangerous). Another factor, hardly discussed in the UK, is research that has emerged at the University of North Carolina which seems to link a strong liking for sugar with alcoholism.

As anyone over 50 in Scotland will tell you, the link between sugar and health was not something they thought about when they were young. Isabel Mitchell, a retired senior nurse and health policy analyst, remembers with happiness her sweet-filled childhood in Dundee - 'dolly mixtures were what I really loved!' Her sugar craving was more easily satisfied because her grandfather owned a newsagent, and she and her sister got to vacuum up the bottoms of the sweetie jars. By the age of 11, Isabel, who is a very trim lady now, was a 'sturdy' child, as the Scots politely put it. 'I had a bit of a rash once, and my mother took me to see this young doctor, who told her that I should be cutting down on the sugar. It was his way of being kind to me, to attribute the rash to the sweeties, rather than that I was chubby. But that was in 1951, and it was a revelation. No one had ever said that to anyone, that sugar was bad for us.'

My mother grew up in rural Ayrshire during the Second World War, and she vividly remembers the driving lust for sugar in all its forms, and particularly for chocolate, which was very rare since the cocoa had to come by ship through submarine-infested seas. Once she and my uncles spent all their pocket money on some strange chocolate they found in amazing abundance in the shop at the nearby railway station - Choc-Lax - it was called. They gobbled it up: 'We were suffering all day!'

'Medicinal sweets' like that were off the ration, and thus the saving of many small businesses - and many sweet-fanciers - during the lean years of the war and after, for rationing of sweets continued till 1953. Irene Birkett remembers the queues stretching down the street each time her grandfather produced a batch of his Glickman's Famous Cough Tablet - no more than a hard fudge with liquorice and aniseed in it, but the medical label allowed Isaac Glickman to get non-rationed sugar and thus his business boomed. Irene and Julie still make the cough tablet at Glickman's - 'It's for winter, but some people eat it all year round!'

The ration for children was a quarter pound of sugar each: my mother and her brothers would stretch out their share in the kitchen, making it into toffee or Scottish tablet, adding bicarbonate of soda to bulk it out and give it bubbles like the inside of a Crunchie bar. 'We brushed our teeth every night, but I think that was about hygiene and breath: we didn't really link it with looking after our teeth. And we expected every annual visit to the dentist in Edinburgh to be agony - you knew you'd get fillings every year, two or three of them.

'But there was a cult of children needing sweeties - and good and kind adults would carry them in their pockets to give to you. And a lot of them were I suppose the worst - boiled sweets - the things I loved like black stripit balls, Berwick cockles and acid drops. But we had no idea.'

Sugar is part of modern Scots history. Every Scot over a certain age gets the same rosy glow when they talk of the sweets of their childhood, of how a quarter-pound of small mint imperials got you 52 sweets. And a glance at the old cookbooks show that sugar has long been a key to Scottish cooking - as garlic was to the people of the Mediterranean, or chilli to the Thais. Shops like Glickman's in Glasgow or the fabulous Candy Box in the seaside resort town of Largs, which stocks an amazing 250 varieties of traditional sweet shops in jars, are testaments to that proud culture and those traditions. And if there's one thing all those Scots sweet-lovers will tell you, after lovingly naming their favourites, it's how happy the sweets made them, even in the hardest times.

Most historians put down sugar's dominance in the Scottish diet to poverty and climate. 'Cold lessens the ability to perceive sweetness,' says Tim Richardson in his excellent book Sweets: A History of Temptation, and suggests this is why Scots and other nations of the far North eat so much more sugar. But this seems oversimple. Stana Nenadic, senior lecturer in economic and social history at Edinburgh University, told me: 'It's very lazy to explain the consumption of sugar as being a matter of poor people in a cold country who need their calories. By the 18th century, enjoyment of sugar was ingrained in the elite culture in Scotland and, as usual, that percolates down to the lesser social strata.' She points to accounts of the fabulous rum-punch parties given by Glasgow merchants of the early 18th century, where sugar, lemons and rum were consumed in amazing quantities. All of these ingredients were flowing into the Clyde from the West Indies, and making those Glasgow ship-owners, refiners and merchants rich.

By the late 18th century, according to one disapproving historian at the time, every farm labourer's wife was taking sugar in their tea. As clergyman David Davies wrote in 1795, 'It appears a very strange thing, that the common people ... should be obliged to use, as part of their daily diet, two articles imported from the opposite sides of the earth.' Sugar was being used by the British in a quantity and a way that no other European nation enjoyed, because they did not have the sugar-producing colonies. And our sugar habit grew very quickly. Economists of the 19th century complained of how the British managed to consume almost all the sugar flowing from the Caribbean: virtually none was re-exported.

The Clyde was the centre of the trade in the nineteenth century and, after sugar-import taxes were halved in 1874, the business got even bigger. By 1878, 16 of Scotland's 17 sugar refineries were around Glasgow: the Clyde town of Greenock was known as 'Sugaropolis' and it was there that Abram Lyle, later of Tate and Lyle, invented Golden Syrup, as a way of using up surplus sugar at a time of glut. (Greenock lost its last sugar refinery 12 years ago, but it's still home to Scotland's last great sweet factory - Drysdale &Gibb, home both of the children's brand Millions and the 'boilings' that have hardly changed in 150 years.) Later the Clyde refined the product of Scotland's sugar-beet industry, which was subsidised by government up until the 1970s.

As a result, for 200 years there was a lot of cheap sugar around the Clyde. Glasgow, followed by the west of Scotland and then the whole country, put it to use, developing the astonishing range jams, puddings, cakes and sweets whose remnants we see today. Sugar, the cheap, easily-digested energy source, fuelled Scotland. By the beginning of the 20th century, jam - which is up to 65 per cent sugar - had become a staple in the diet: the 'jilly piece', a jam sandwich, the basis of a working man's lunch. (And so the best marmalade still comes from Dundee.) And, of course, the problems we ascribe to excessive consumption of sugar followed. Even today, it's notable that national dental-decay rates in five-year-olds spike in places like Bristol and Merseyside, which were also centres of the sugar trade. (These also have inner-city areas known for their deprivation - but Newcastle, a port city which did not have a sugar trade, has a much lower d3mft rate.)

But even if sugar was the aspirational food ingredient of the 18th and early 19th century, its association with poverty became clear in the 20th - first by social historians and activists during Glasgow's long decline, and then in the late Sixties, by health campaigners. But the links between sugar consumption, poor health and bad teeth are still blurred. The Scottish Executive's current strategy document - Towards Better Oral Health in Children seems unable to make up its mind. 'Dental disease in childhood may be broadly attributed to a high sugar diet ... ' it states. But, two paragraphs later: 'Deprivation is a key influence in the emergence of dental and oral disease.' So which gives you bad teeth? Being poor or eating too many sweets?

If you delve into the vast mess of statistics produced in Scotland on oral health, one sure fact can eventually be pulled out, clean and shining: the rich do have better teeth - much better. In Scotland's best-off areas the national target of 60 per cent of five-year-olds with no dental-decay damage has already been reached - in the poorest, the rate is still down at 25 per cent. But how much has this to do with sugar consumption? Is the key fact not that the rich brush their teeth more and visit dentists more frequently?

Tim Richardson sums up modern medical thinking: 'Sweets are not the only culprit with tooth decay: starchy foods like crisps have been identified as at least as bad and possibly even worse. Unsweetened as well as sugary breakfast cereal and even bread also trigger acid attacks on the teeth.' The fact is that all carbohydrates rot teeth, and sugar is merely a easily reduced carbohydrate among the many that make up the bulk of our daily energy intake. Whether it's 'natural' or refined, glucose, sucrose or fructose, makes little difference. And then we have to take on board the evidence that, even though children's sugar intake has doubled in the last 25 years, their teeth have been improving, at least since the mid-Nineties.

This all means that sugar consumption is just not that important in oral health. Americans eat a lot more sugar than the British - 40kg per annum to 34kg here - yet it's our teeth they laugh at. Having disease-free teeth is about a lot of factors - hygiene, dental care, orthodontics, genetics, fluoridation, but diet looms pretty small among them. Boringly, the recipe for no fillings is what it always was: lots of brushing and regular visits to the dentist.

And there the poor remain at an awful disadvantage. For a long time, health-policy experts were confused: it was thought that Scotland's most disadvantaged were actually rather well provided for. There are more dentists in Glasgow than anywhere else in Scotland - seven and a half per 10,000 people. (The UK average is 5.2, and in Scandinavia, where they have lovely teeth, nearly 12.) But in 2004 researchers found a new way of looking at the figures. If you adjusted them for levels of need, then in poorest Glasgow there are only 1.79 dentists per 10,000 people. That's a figure from the third world: better than Iraq (where it's 1.1 dentists per 10,000) but not as good as Grenada. The Scottish Executive is now offering a bounty of up to 50 per cent on top of normal fees for dentists who treat under-five-year-olds in Scotland's poorest areas.

I'm sitting here chewing on a packet of Original Hokey Pokey that I bought down the road from our flat in Edinburgh. It's sort of cockroach-coloured and looks like decayed concrete; it has a glorious semi-toasted caramel taste and, once chewed, cannot be removed from the teeth in less than five minutes. The ingredients are refined and soft brown cane sugar, glucose, sodium bicarbonate and honey ... and on the label it says 'Hokey-Pokey, penny a lump, the more you eat, the more you pump'.

I'm not sure quite what that means, but if they're referring to the sugar rush, they're not exaggerating: I can see how Clydesiders used to build ships on similar fuel. Dr Marsh at the Social Issues Research Centre in Oxford is a bit of a sweet-head: he told me he can do The Observer's Everyman crossword faster just after he's eaten a Mars Bar. So I'm maxing on sugar in order to try and get this article finished.

Downstairs my son is sucking on a Glickman's Granny Sooker - a boiled sweet so named because, according to Irene Birkett, 'when you suck on it, it's that sour your face looks like an old granny's'. Occasionally he stops to have a go at the gobstopper I got him at the Candy Box in Largs. It's too big for a seven-year-old mouth, so he is using his beautiful, cavity-free white teeth to grind at it till it becomes a feasible size. It's going to take a while, but I've been forced to admit to him that my research shows this is all fine - so long as he brushes his teeth immediately afterwards. And my wife has just told me about high school in Cincinnati, where she went from Newcastle when she was 12, and how she was mocked by the other girls because she didn't carry toothbrush and toothpaste in her bag for use through the day. She has perfect American teeth now, and when she says 'Imagine that in a British school - peer pressure that makes you brush your teeth!', I wonder if she might be on to something.

Glickman's, www.glickmans.co.uk.

· Alex Renton is the winner of this year's Glenfiddich Trophy for his outstanding features for OFM