KEY POINTS:
When school students slake their thirst with a cold Diet Coke after a hot summer lunchtime on the playing field, few are likely to consider the cocktail of controversy they are drinking.
The Government thought it was on to a public-health winner this week in securing the voluntary agreement of Coke and Pepsi's suppliers to withdraw their full-sugar fizzy and energy drinks from schools by 2009.
But when the Ministers of Health and Education had finished promoting the novelty of their anti-obesity deal, health campaigners started howling that it was a lost opportunity because diet drinks would continue to be available.
Coca-Cola Amatil and Frucor Beverages intend to continue selling fruit juice and carbonated diet drinks, several of which contain caffeine.
Green Party health spokeswoman Sue Kedgley complained of children continuing to be exposed to the caffeine, acids and artificial sweeteners like aspartame in diet drinks.
Health experts have backed some of her concerns but the soft-drink industry rejects them.
Diet Coke's ingredients include phosphoric acid, citric acid, caffeine and the sweeteners aspartame and acesulphame potassium.
Dentist and AUT University lecturer Callum Durward welcomed the deal but said dentists would like diet drinks, sports drinks and fruit juice removed too.
He said the sugar in soft drinks was a major contributor to decay in teeth, but diet drinks, sports drinks and juice, without added sugar, were acidic.
The acid ate into the enamel - the hard, outer layer of teeth - and could expose the softer dentine underneath. Teeth could become smaller and jagged, overly sensitive to hot, cold and sweet food and drink, and were at higher risk of decay.
"We are finding around the world in studies more dental erosion caused by acidic drinks and loss of enamel. We see this in wine-tasters; wine is quite acidic."
Badly eroded teeth could need expensive repairs such as veneers or crowns. With little over 50 to 60 per cent of teenagers accessing state-paid dental care, many reached their 20s needing teeth extracted and a mouthful of fillings.
"I believe drinks are a large part of the problem. I would recommend a diet drink over a sugar-containing drink, but you can still get into trouble with diet drinks."
Coca-Cola Oceania spokeswoman Alison Sykora said Diet Coke and Coke Zero were reasonably acidic.
"It's the same level of risk as eating or drinking anything of a similar acidic nature and that would be less than consuming an orange."
Dietitian Rob Quigley disagreed. He said some of the acid in an orange was held in cells not broken open until they reached the stomach - and oranges provided nutrients not found in diet soft drinks. He said caffeine was associated with irritability in children and phosphoric acid could affect bones.
American researchers this month linked high consumption of cola soft drinks to loss of bone density in older women. They suggested phosphoric acid - unlikely to be found in non-cola fizzy drinks - might be a cause. But they also noted the mixed results of earlier studies.
Soft drink makers replied that their products were a minor source of dietary phosphorous, the main ones being cereal and milk products.
Of caffeine, Ms Sykora said Coke had 75 per cent less than the same volume of coffee and was fine for children unless they were sensitive to it.
