Artificial food colourings should be banned in the interest of public health, say UK experts.
Artificial colourings increased hyperactivity levels
A team of researchers from Southampton University said removing these substances from foods could cut hyperactivity rates in young children.
They are extending their research to see whether additive-free diets have a positive effect in older children too.
The research on 300 three-year-olds appears in the journal Archives of Diseases in Childhood.
Professor John Warner and colleagues screened the children for hyperactivity and allergies.
They then divided the children into four groups - those with both hyperactivity and allergy, those without either, those with allergy but no hyperactivity and those with hyperactivity but no allergy.
Over the next four weeks the researchers controlled the children's diets.
For the first week, the children ate only foods free of artificial additives.
During the second and fourth weeks the children were given a fruit juice with or without artificial colourings and preservatives.
The children's parents were asked to keep diaries on their child's behaviour throughout the study, but were unaware which type of juice their child had been given.
Overall, the parents said their children became less hyperactive during the period when the additives were removed.
Similarly, they said their children were much more hyperactive during the period when the additives were put back in.
This was regardless of whether the child was hyperactive or allergic before the study.
However, trained doctors doing formal assessments of the children did not find any change in behaviour with change in diet.
Professor Warner believes parental ratings might be more sensitive because parents see their children's behaviour over a longer period of time and in more varied settings.
But he says more research is needed to determine this, and also whether older children's behaviour might be affected by additives in a similar way.
He is now planning a longer term study, to start in September, involving about 900 three- to nine-year-olds.
"We are trying to get some more hard evidence.
"I want this to address a fundamental issue which is 'Why do we have to have coloured food?'
"Why can't people have pale salmon rather than pink salmon?
"It's absolutely imperative to have follow up studies because we are not now just talking about a population of children with a particular problem we are saying there's a potential for this to be an effect on all children.
"And if that really is the case reproducibly, then food colouring should be removed," he said.
The Food Standards Agency said: "All additives must pass strict safety checks before they can be used in foods and if any new evidence were to emerge from this or other work their safety would be reviewed."