Dentists' warning on smoothies and juices: popular drinks more acidic than vinegar

The concerns were raised as official figures disclosed that dental problems have become the third most common reason for children to be admitted to hospital.

An investigation by The Sunday Telegraph reveals the acid levels of popular juice drinks consumed by millions of households – including one found to be more acidic than vinegar.

Dr Kathy Harley, dean of the dental faculty at the Royal College of Surgeons, said many parents encouraged their children to drink smoothies and juices every day, unaware that the combination of high acid levels and sugar content can destroy young teeth.

Instead of giving children the apparently healthy snack of fruit juice and a box of raisins, it would be better for their teeth if they were given a glass of water and a handful of chocolate buttons, she said.

Manufacturers are required to publish information about the nutritional content of drinks on the label – but not their levels of acid, which can erode the surface of teeth, making decay more likely.

Dr Harley said 50 per cent of five-year-olds now have signs of damage to their tooth enamel caused by excess acid in their diet.

She said that while health-conscious parents had the best of intentions in trying to follow the Government's "five a day" advice for feeding their children fruit and vegetables, in fact the combination of acid and sugar in juice drinks meant they should be restricted to a "once a week treat".

Tooth enamel begins to be destroyed when acid levels in the mouth drop below 5.5 on the pH scale, which has 7 as neutral and 1 as strong acid.

While water has a pH of 7, and milk is just below at 6.8, our investigation found that a soft drink called This Water with lemons and limes, which describes itself as a "juice drink blended with pure squeezed juices and pure spring water", had a level of 2.7 – making it more acidic than cider vinegar, which had a level of 2.9.

This Water also contains 9.5 teaspoons of sugar in a 420ml (14.7 fl oz) bottle. In 2008, the company, which is part of Innocent Drinks founder Richard Reed's empire, had an advertisement campaign banned by the Advertising Standards Authority for failing to inform consumers about the sugar content of its juice drinks.

The products were advertised with the strapline: "Simple, natural, refreshment" in posters which stated that the drink was made from water and fruit but made no mention of added sugar.

The other fruit drinks tested, including Tropicana orange juice, Copella apple juice, Innocent smoothies, Capri Sun orange drink and Robinsons Fruit Shoot apple and blackcurrant low sugar drink all had acid levels ranging between 3.3 and 3.8.

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The most acidic beverage tested was Coca Cola, with a pH level of 2.5 and 12.5 teaspoons of sugar in a 500ml (17.5 fluid ounces) bottle.

Dentists said that rather than consuming fruit or fruit juices as a snack, they were better consumed at meal times or accompanied with something containing calcium, such as cheese, which neutralises acid.

Children should be encouraged to drink water afterwards to wash away some of the acid, but not to brush their teeth until at least an hour afterwards, as teeth are weakened by exposure to acid, they said. Saliva also helps to restore the balance.

Statistics disclosed in parliament by the Department of Health show that the most common reason for children to be admitted to hospital in England in 2011-12 was viral infections, followed by disorders related to premature birth. Dental caries was the third most common cause.

In the two previous years, dental problems were the fourth most common reason for such admissions, with upper respiratory infections a more likely cause.

Separate NHS figures show that dental disease is the most common reason for any child to be given a general anaesthetic, with a least 155,000 such cases a year in England involving children aged 12 or under.

Government health advice states that everyone should have five portions of fruit and vegetables a day, and that one 150ml glass of fruit juice can count as one portion.

Dr Harley said she did not disagree with the overall advice, but that it would be better if children met the target by eating fruit and vegetables with meals, and only had juice occasionally.

She said: "The only healthy drinks for teeth are milk and water. Children are having fruit drinks and smoothies several times a day, when they these should be considered as a treat, something to have once a week."

"The dental needs are greatest in areas of social deprivation but there are also a lot of cases in every social group where parents are trying to do the right thing, but are acting misguidedly, thinking that the juices and smoothies are the best thing."

Dr Harley said smoothies and juices should be marketed as treats, rather than health fare, and that schools should only offer children milk or water.

The senior dentist also said parents should brush their children's teeth for them until they reach the age of seven or can demonstrate manual dexterity by writing their own name clearly.

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A spokesman for This Water drinks said the products were "not meant for children and are not marketed as such".

He added: "This Water drinks are 100% natural and the recipe in question is made with fresh lemon and lime juice so it is going to have a natural acidity."