The truth about fluoride in water, explained by our science editor

Now, though, the position is somewhat reversing. Britain is preparing for the biggest expansion of fluoridation since the 1980s, in what backers describe as the “single most effective public health measure” available in the battle against tooth decay.

On the other side of the Atlantic, meanwhile, the incoming Trump administration has vowed to remove it from the water. Robert F Kennedy Jr, Donald Trump’s pick for health secretary, has described fluoride as “an industrial waste” responsible for neurodevelopmental disorders, cancer and decreased IQ.

Does he have a point? What’s the truth about fluoride in the water?

Despite a decades-long campaign to highlight the alleged risks, there is limited evidence that fluoride salts — at the low levels in which they are added to water — actually carry any risk to cognitive or physical health. In some cases too much fluoride can cause white flecks on the teeth, called fluorosis, but usually this is barely noticeable.

In September, a federal court in California ruled that the Environmental Protection Agency should look at the matter again, but was careful to say its ruling “does not conclude with certainty that fluoridated water is injurious to public health”.

The US Centers for Disease Control and Prevention repeatedly declared fluoridation one of the greatest public health achievements of the 20th century. British dentists say it is very helpful and generally view America’s next health secretary as a crank. “RFK Jr’s views break from a clear scientific consensus that water fluoridation is both safe and effective,” says Eddie Crouch, chairman of the British Dental Association. “We believe public health policy should be led by the evidence, not the tinfoil hat brigade.”

Yet in Britain, too, concerns persist. The slow, piecemeal introduction of fluoride, which is also present in most toothpaste, has been delayed by worries about its side effects. While most scientists are confident it is safe, a small body of evidence has emerged that suggests that at very high levels — higher than that in tap water — fluoride might affect development of young brains.

Communicating this type of risk is a minefield for scientists, which opens the door for organised opposition. “There’s a small group who opposes it in the UK and they’re very mobile,” says Dr Charlotte Eckhardt, dean of the Faculty of Dental Surgery at the Royal College of Surgeons. “Every time an area is thinking about doing it, they tend to mobilise themselves and protest against it.”

While the city of Birmingham was an early adopter in 1964, fluoridation spread in the Seventies and Eighties only to segments of the Midlands and northern England, and then stopped. Only six million people in England have added fluoride, and those in Scotland, Wales and Northern Ireland have none. Some areas have water high in fluoride thanks to underlying geology, but only 300,000 people live in places where the water naturally reaches the levels that fluoridation schemes seek to achieve.

Tooth extraction rates in the West Midlands are now some of the lowest in the country, less than half those seen in Greater London. Of course, fluoridation is not the only factor, but it is tempting to conclude that the residents of Birmingham are now reaping the rewards of six decades of public health policy.

The London Assembly looked at following their lead in 2003, but its health committee concluded that it would be politically and technically difficult, and recommended alternative measures for dental health before fluoridation was “even considered”.

Others have also found it difficult. When fluoridation was proposed in Glasgow in the late 1970s, a legal objection from a single resident led to a five-year battle with Strathclyde regional council, which it lost on a technicality, halting plans across the rest of Scotland. Southampton considered adding fluoride in the late 2000s but gave up after years of local opposition led by the Green Party.

Now there are attempts to add fluoride in new areas, including in parts of the northeast, Cumbria, North Yorkshire and Cornwall. But opposition persists. Dianne Standen, from the campaign group Fluoride Free Cumbria, told the BBC that the government “should not put it in the water until you’ve established 100 per cent safety”.

Advocates say putting a health-boosting additive in the water is cheap, cost effective and repays itself many times over in savings to the NHS. Critics say adding chemicals to tap water, something every family needs, represents the most insidious removal of choice.

But officials are determined to push on. The potential benefits, health bosses say, are significant.

Sir Chris Whitty, the chief medical officer for England, published a report with his counterparts in Scotland, Wales and Northern Ireland in 2021 estimating that raising fluoride levels from up to 0.2mg per litre to 0.7mg/l could result in cutting child admissions for tooth extractions by as much as 68 per cent. It’s estimated that such a measure would lead to the number of five-year-olds with tooth decay falling by 28 per cent in the most deprived areas.

Eckhardt, who does her surgical work in Swansea, says it is easy to assume that in an era of modern toothpaste, which contains fluoride, putting the mineral in water should be unnecessary. “I have children coming in who brush their teeth just once or twice a week,” she adds. “There are huge pockets of poverty and some individuals have to make a decision: do they buy toothpaste, or do they put food on the table?”