Flat or fizzy drinks don't offer proper rehydration to children with stomach bugs.

British researchers who searched the scientific data for evidence found that flat soft drinks - a home remedy for diarrhoea and vomiting - prevents dehydration in children with gastroenteritis.

Researchers at the children's emergency department at Watford General Hospital posed a single clinical question: In children with viral gastroenteritis, do flat, fizzy drinks such as Coca-Cola offer adequate rehydration compared to oral rehydration solutions available in drug stores?

They searched the literature as far back as 1950. Only a few relevant papers were found, mainly offering opinions. So they analyzed a sample of Coca-Cola and then looked for information about the content of other different types of liquids - oral rehydration solution, Pepsi-Cola, Schweppes Lemonade, Sprite and 7Up - and compared them.

According to their report, biochemical analyses clearly show that various carbonated drinks contain low levels of sodium and potassium, and far more sugar than oral rehydration solutions. Cola contained up to seven times the amount of glucose the World Health Organization recommends for oral rehydration.

"They are potentially harmful because they're much more concentrated and there's a lot more sugar in there," says Dr. Michelle Jacobs, a consultant in emergency medicine at Watford General Hospital. "Really, you're just giving yourself a huge sugar load."

The researchers conclude that carbonated, flat and other drinks, including cola, provide inadequate fluid and electrolyte replacement and cannot be recommended.

What's more, "if it went on for long enough and a child was using these things for long enough, they could end up in a worse situation, medically, than they started off because of an imbalance of their sodium and potassium." She understands that parents can be desperate to get some fluids into a sick child, and will try "whatever they have at hand."

"Most parents know they shouldn't give them just plain water," she says. (Water by itself doesn't contain enough salt and nutrients to help with dehydration.) And oral hydrating solutions "are not that palatable, children just half the time don't like them."

"So they try to give them something else with a little bit of sugar, maybe, to give them a bit more energy and they know that children like fizzy drinks. And it's just kind of handed down from generations and families and neighbours that it's a good thing to do. But there's no evidence for it."

The Canadian Paediatric Society has for years recommended parents avoid giving their children sugary drinks, including fruit juice or soft drinks, if they have diarrhoea or are vomiting.

Past-president Dr. Robert Issenman says the specially formulated oral solutions containing electrolytes have been very effective in cutting down the number of children who get sick enough they need to be admitted to hospital.