The 'controversial' history surrounding adding fluoride to tap water

Fluoride has a controversial history. So what is fluoride and should we be worried about the potential risks?

Fluoride is a naturally occurring element that has been added to tap water in some parts of the United States since the 1940s.

This element is endorsed by the American Dental Association, the American Academy of Pediatric Dentistry, and the Canadian Dental Association for its effectiveness in preventing tooth decay.

The US Centers for Disease Control and Prevention lists water fluoridation — adjusting fluoride levels in tap water supplies — as one of its top 10 public health achievements.

However, fluoride has a controversial history. So what is fluoride and should we be worried about the possible risks?

What is fluoride?

Fluoride is a naturally occurring element found in soil, rocks, and water.

'Every water source has some amount of fluoride,' says Steven Levy, professor of preventive and community dentistry at the University of Iowa. It's even in tea.

Eating foods containing refined carbohydrates — such as bread, yogurt or fruit — causes bacteria to produce acids that demineralize tooth surfaces, creating microscopic cavities.

"Fluoride speeds up and enhances the remineralization process, so most people never get cavities," he says.

Several countries, including the US, UK, Spain and Brazil, have local jurisdictions that add fluoride to water to prevent tooth decay. Germany has added fluoride to salt since 1991.

"All water sources contain some amount of fluoride.

Add fluoride to water

In the early 1900s, researchers realized that people in areas with high levels of natural fluoride in the water system were more likely to develop dental fluorosis. This condition usually affects children who are exposed to too much fluoride while their teeth are developing.

Dental fluorosis is a condition where the enamel of the teeth is 'mottled' , according to John Morris, senior lecturer in dental public health at the University of Birmingham in the UK.

The condition causes white spots or streaks on your teeth, says Cheryline Pezzullo, MD, professor at New York University College of Dentistry.'

However, people with fluorosis also have much lower rates of tooth decay due to the low levels of natural fluoride in the water.

American scientists concluded that , at concentrations of about one part per million , fluoride in water protects against tooth decay without causing fluorosis. Today, the recommended concentration in the US is 0.7 parts per million because people also 'absorb' fluoride from toothpaste and mouthwash.

Safe dosage

Fluoride is a natural component of bones.

'There is no vertebrate—human, animal—that does not have fluoride in its skeletal system,' says Howard Pollick, a dental scientist at the University of California, San Francisco. Long-term exposure to fluoride at concentrations above four parts per million can cause fluorosis, a disease that weakens bones.

This figure significantly exceeds the World Health Organization (WHO) recommended level of 1.5 milligrams per liter, as well as the US Public Health Service's recommended level of 0.7 milligrams.

Morris said the level 'sufficient' to develop bone fluorosis could be "drinking large amounts of tea or 'eating' several tubes of toothpaste a day". Any substance can be toxic at high concentrations - even water. "It's not the substance, it's the dose," Pollick said .

Concerns about fluoride

People have been worried about fluoride since it was first added to water. Some opponents worry that fluoride fumes are deadly, while gum disease advocates are 'quite concerned that people will now just rely on fluoride in their water and not brush their teeth,' Pollick says.

There are also concerns about cancer risks. A 1990 study found an increase in bone tumors in rats exposed to high levels of fluoride.

But a Public Health Service report, based on more than 50 population studies, found no 'detectable cancer risk to humans' at low fluoride levels.

(Source: The New York Times/National Geographic).

There has been recent debate about the link between fluoride exposure and children's IQ. A 2021 study linked high fluoride exposure to lower IQ in boys, while a 2023 meta-analysis found no link.

A report by the National Toxicology Program has " moderate confidence" that fluoride above WHO recommended levels may affect children's IQ.

Prevent tooth decay

Tooth decay rates have declined, but it remains 'one of the most common chronic diseases, and remember [tooth decay] is completely preventable in children,' Morris said. He said tooth decay affects children's education, diet and overall development.

After the Canadian city of Calgary removed fluoride from its water, tooth decay in children became more severe.

For those who do not have easy access to or cannot afford dental care, tooth decay is a huge 'burden' .

'Tooth decay can lead to infection and pain, and the infection can spread to other parts of the body,' says Pezzullo .

Adding fluoride to water is a cost-effective preventative measure, Levy says. 'All you have to do is drink water.'

The controversy surrounding fluoride

Fluoride can be a controversial subject, especially in the US. Some people in the 1950s believed it was a 'plot' to poison America, while others said it was a way for the sugar industry to sell more sweets.

There has been a strong backlash against fluoride since water levels were first regulated. 'I think talking about putting something in water is a pretty sensitive issue for some people,' Morris says.

'People feel like it's an invasion of personal freedom ,' Pezzullo said.

Morris says other public health decisions – such as vaccines and seat belt laws – have received similar pushback. 'The development of clean drinking water in the 19th century was also controversial.'

'We should not disrupt [public health programs] based on minority opinion,' he said .

Pollick agrees, saying: 'Overall, the scientific community is unanimous in supporting the appropriate and judicious use of fluoride.'