HEALTH warnings could be placed on tubes of fluoride toothpaste sold in Britain after the issue of a United States alert on the dangers of swallowing the chemical.

At least one supermarket chain is considering changes after the Washington-based Food and Drug Administration set out a stringent new labelling requirement. Fluoride toothpaste sold in the US will now carry the warning: "If you accidentally swallow more than used for brushing, seek professional help or contact a poison-control centre immediately."

It is the first time the word "poison" has been used. Previous advice simply said: "Don't swallow. Use only a pea-sized amount for children under six." Details of the development follow fresh controversy over new evidence that fluoride in toothpaste and water supplies is potentially harmful.

Peter Mansfield, president of the National Pure water Association, and Paul Connett, professor of chemistry at St Lawrence University, New York, presented research last week showing the chemical can cause cancer and damage to the brain and immune system.

However, the claims were dismissed by eight leading medical organisations, including the British Medical Association and the British Dental Association. Last night, a spokeswoman for Sainsbury's supermarkets said: "We are seeking clarification from the FDA to see why they have used this new warning. Obviously, if there is new evidence on the dangers of fluoride, we would consider changes in labelling."

Meanwhile, British health officials continue to stress the benefits of fluoride in preventing tooth decay. Government scientists say that a two-year-old child would have to eat one-and-a-half large tubes of toothpaste before suffering any toxic effects.

But this is disputed by Dr Mansfield, who thinks government recommendations of fluoride levels are unsafe. Data on more than 600 of his patients in the Midlands cast doubt on previous assurances that water fluoridation cannot harm the skeleton.

"Research shows fluoride accumulates with age. We are sitting on a time bomb, and we will see the effects of this in 20 years' time, with millions of people suffering from backache or crippling osteoporosis as a result of fluoride levels," he said. He wants to see a health warning on all items containing fluoride.

Diana Scarrot, the British Dental Association's head of education and science, said it would be issuing recommendations on labelling to the toothpaste industry in the autumn to enable customers to choose low-fluoride brands if they wished. She said: "If there was evidence that fluoride was doing something harmful we would act upon it."