TAP water could be lowering children’s intelligence, leading experts have warned.

Top doctors claim fluqride in drinking water can interfere with a child’s brain function. They believe this can lower IQ levels and lead to behavioural problems.

Last night Dr Vyvian Howard, an expert in chemicals and infant health at Liverpool University, told of his concern. He said: “Babies are on a wet diet for the first four months. If they drink infant formula they get fluoride through tap water, which is toxic and can affect brain development.

“We know mothers screen out fluoride, preventing it from getting into breast milk. This is a natural evolutionary process to protect them. Fluoride is not safe for babies.”

Ten per cent of the country has fluoridated tap water to keep teeth healthy and the Government plans to extend coverage under a new act now passing through Parliament. Fluoride is also added to toothpaste and is found in tealeaves, fertilisers, pesticides and air pollution. Doctors think there are so many sources that children could also be overdosing.

Dr Peter Mansfield, a GP and director of the Good Health Keeping service at Louth, Lincolnshire, studied more than 100 children with behavioural problems.

He discovered those with high levels of fluoride in their bodies were more likely to have developmental and behavioural problems.

Once the fluoride was taken out of their diet they got better.

He said: “This is very worrying. Fluoride is toxic and could cause mental problems. It could be that thousands of children are underperforming as a result. We had children we thought were affected by fluoride. In some cases they were hyperactive, lacked concentration and were unhappy all the time.

“We tested them and quite clearly demonstrated that fluoride was causing their problems. “The trouble fluoridated water is causing far outweighs the possible benefits to children’s teeth. Nothing like enough work has been done on this and no one is checking – it’s very worrying.” His findings are borne out by a Unicef-backed study of 769 schoolchildren in China. It found those with mental retardation or low IQ levels had excess fluoride in their systems.

The study concluded that the chemical makes mental health problems worse by interfering with the cen-tral nervous system. Another study carried out in America found that rats behave like hyperactive children when given a comparable amount of fluoride.

Some experts including Dr Howard also fear fluoride is fuelling rising obesity levels. They think it interferes with the body’s hormone balance, especially the thyroid gland, which controls weight gain.

Medical author Dr Barry Durrant-Peatfield said: “Fluoride disrupts the hormones that control the thyroid gland. This causes an underactive thyroid which leads to obesity, tiredness and depression.”

And Dr Howard said: “Fluoride was once used as a medicine to treat thyroid overactivity.”