Alan Johnson, the Health Secretary, has been accused of overstating the benefits of adding fluoride to water in the fight against dental disease.
Tooth decay in children across Europe has fallen irrespective of whether there is fluoride in the water, authors of a report have said.
Mr Johnson has called for it to be added to all water supplies in the United Kingdom in an attempt to reduce the number of people seeking dental treatment.
He said children in Manchester, where water is not fluoridated, were twice as likely to have tooth decay as those in Birmingham, where it is added.
Mr Johnson said a review of evidence by York University had found that adding fluoride reduced the number of children with tooth decay by 15 per cent.
But the authors said their findings have been used selectively and the impact of adding fluoride to water supplies was unclear. They accused the Government of giving “an over-optimistic assessment of the evidence in favour of fluoridation“.
“The Department of Health’s objectivity is questionable,” said Sir Iain Chalmers, the editor of the James Lind Library in Oxford, and Prof Trevor Sheldon, the deputy vice-chancellor at York University, who conducted the review.
They said tooth decay in 12- year-olds has reduced across Europe irrespective of whether there is fluoride in the water.
The countries with the biggest drop in childhood tooth decay – Sweden, Netherlands, Finland and Denmark – do not fluoridate the water.
They said levels of tooth decay have fallen greatly in the past 30 years.
“This trend has occurred regardless of the concentration of fluoride in water or the use of fluoridated salt, and it probably reflects use of fluoridated toothpastes and other factors, including perhaps nutrition.”
Evidence about the potential harm of adding fluoride to the water – some studies have suggested a link to bladder cancer and hip fractures – was not of sufficient quality to draw firm conclusions, Sir Iain and Prof Sheldon said.
Writing in the British Medical Journal, they said: “Evidence on the potential benefits and harms of adding fluoride to water is relatively poor.”
Across the United Kingdom 5.5 million people use water with added fluoride and another half a million use a water supply where it occurs naturally.
Over the next three years, £14 million will be available to strategic health authorities which decide, after local consultation, to add fluoride.
Mr Johnson said: “Fluoridation is scientifically supported, it is legal, and it is our policy, but only two or three areas currently have it and we need to go much further in areas where dental health needs to be improved.
“It is an effective and relatively easy way to help address health inequalities – giving children from poorer backgrounds a dental health boost that can last a lifetime, reducing tooth decay and thereby cutting down on the amount of dental work they need.”
A spokesman for the Department of Health said it “made no apologies” for “promoting the benefits to oral health which fluoridation offers”.
“No evidence of risks to general health have been identified at the 1 part per million concentration used for artificially fluoridating public water supplies,” he said.
“Nevertheless, the department is committed to further research to strengthen the evidence base on the effects of fluoridation.”