Children should not be given "flat" fizzy drinks to help them rehydrate after vomiting or diarrhoea, researchers from Watford General Hospital have said.

Drinking flat cola and similar drinks are often used to provide youngsters suffering from acute gastroenteritis with additional fluids.

But these are an inappropriate substitute for oral rehydration solutions, which contain the right balance of salts and sugars needed, warned Consultant Paediatrician Dr Ashley Reece and Dr Michelle Jacobs, a consultant in emergency medicine.

The eight-month study, conducted by Dr Reece and Dr Jacobs, who both work in the children's emergency department at Watford General, in Vicarage Road, aimed to solve the question "Does drinking flat cola prevent dehydration in children with acute gastroenteritis?"

Dr Reece said: "As frontline clinicians, we see a lot of children with gastroenteritis, and an old wives' tale that people pick up on and use is when a child is having diarrhoea and vomiting, parents sometimes decide that giving them flat or fizzy drink is a good way to prevent dehydration when they're losing a lot of fluid."

The authors concluded there was little information available from previous clinical studies on the effectiveness of using carbonated drinks compared with oral rehydration solutions, but found there were many scientific studies that demonstrated how inappropriate they were.

Oral rehydration solutions, which are available from chemists and by prescription from doctors, contain a balance of salts and sugars to replace those lost during illness, while carbonated drinks are low in sodium and high in glucose.

Dr Reece said: "The bottom line is there's little information about the effect of using carbonated drinks compared to oral rehydration solutions, but lots to suggest it's inappropriate to use.

"Fizzy drinks are higher in sugar and more appealing to taste, but don't contain enough minerals. There is a danger it could dilute and deplete existing levels and cause other complications and make them more poorly."

Dr Reece added that their findings met with their expectations. He said: "If a child has gastroenteritis, then it's inappropriate to give them these drinks."

The advice is published in the May issue of Archives of Disease in Childhood.