‘The science of fluoride is starting to evolve’: behind the risks and benefits of the mineral

A national conversation about fluoride’s health benefits exploded this fall after a federal toxicology report, court ruling and independent scientific review all called for updated risk-benefit analysis.

Fluoride, a naturally occurring mineral in some regions, has been added to community water supplies since the mid-20th century when studies found exposure dramatically reduced tooth decay.

The controversy, heightened by description of the mineral as “industrial waste” by Robert F Kennedy Jr, Donald Trump’s pick to lead the US health department, highlights questions some towns are now wrestling with: should the mineral’s well-established protective effects against tooth decay be prioritized lest Americans, and especially children, be subject to unnecessary pain and shame from an unhealthy smile? Or should the possibility of neurodevelopment effects be prioritized, even as studies continue?

“Fluoride is the perfect example of helping people without them even having to do anything,” said Dr Sreenivas Koka, the former dean of the University of Mississippi Medical Center’s school of dentistry. The state is a “dental desert”, where there is only one dentist for every 2,120 residents. “Fluoride in the water – all you have to do is drink water and you’ll get the benefit.”

Fluoride is added to about 72% of community water supplies in the US, according to the Centers for Disease Control and Prevention (CDC). The CDC again endorsed the practice in a scientific statement this May, saying it found no “convincing scientific evidence linking community water fluoridation with any potential adverse health effect or systemic disorder such as an increased risk for cancer, Down syndrome, heart disease, osteoporosis and bone fracture, immune disorders, low intelligence, renal disorders, Alzheimer disease, or allergic reactions”.

Still, controversy over water fluoridation recently made headlines after two high-profile reports and a federal court ruling. The US National Toxicology Program set off a firestorm in August when it published a systematic review that found with “moderate confidence” that children exposed to fluoride levels twice those recommended for drinking water (1.5mg per liter versus the recommended 0.7mg per liter) “are consistently associated with lower IQ in children”.

Then, in October, a new Cochrane Review lowered the estimated impact of fluoride, citing the widespread use of fluoride in toothpaste beginning in 1975.

“Studies conducted in 1975 or earlier showed a clear and important effect on prevention of tooth decay in children,” Cochrane Review researchers wrote. “However, due to the increased availability of fluoride in toothpaste since 1975, it is unlikely that we will see this effect in all populations today.”

The public debate comes as the National Institutes of Health (NIH), the world’s largest publicly funded research agency, is both a key funder of research advancing society’s understanding of fluoride’s non-dental health effects and an agency squarely in Trump’s crosshairs.

The agency is one of the top targets for cuts and restructuring. Paradoxically, that could mean that critics such as Kennedy cut research on fluoride, even as the NIH funds research into potential detriments. The incoming administration has not made proposals on how to improve oral health in the US.

Fluoride’s health benefits were investigated in the early 20th century, when a Colorado Springs dentist questioned why town residents had brown, mottled and decay-resistant teeth – now known as fluorosis.

It was later found that fluoride naturally occurred at high levels in Colorado Springs, causing the cosmetic defects. Its decay-resistant properties were confirmed in a landmark 1945 study in Grand Rapids, Michigan, which found children in Grand Rapids were 60% less likely to develop dental caries (better known as cavities) with fluoride added to water.

By 1999, the CDC hailed water fluoridation as one of public health’s greatest victories, alongside seat belts and vaccination. That view was buttressed by a 2015 Cochrane Review, considered the gold standard, that found fluoridating water at 0.7mg per liter led to a nearly 26% reduction in tooth decay, a figure still cited by the American Dental Association (ADA) and American Academy of Pediatrics (AAP) today.

The need for preventive oral health solutions is profound in the US – more than 68 million people lack dental insurance and about one in four adults said in a survey they have avoided the dentist because of cost.

In addition, school children lose an estimated average of 34m school hours each year due to unexpected dental visits; 2 million Americans visit the emergency room each year because of tooth pain; half a million travel abroad for cheaper care and one in five American seniors lack a single natural tooth. Lack of dental access is so common in some areas, doctors in prison frequently have patients who have never seen one.

“One of the things I routinely ask young people in juvenile jail is: ‘Do you have a doctor? Do you have a dentist?’” said Dr Fred Rottnek, former medical director of St Louis county jails in Missouri and now a professor of community medicine at Saint Louis University School of Medicine. “A lot of them have never reported going to the dentist.”

Modern inquiry into fluoride’s non-dental health effects began to pick up pace in 2015, when the National Toxicology Program (NTP) requested a systematic review on fluoride’s impact on neurodevelopment. By 2019, toxicology researcher Bruce Lanphear, of Simon Fraser University in Canada, co-authored a study finding fluoride exposure was associated with decreased IQ, which would later be incorporated into the NTP’s systematic review.

“That gives you an indication that the science of fluoride is starting to evolve – it wasn’t set in stone 70 years ago,” he said.

Lanphear, and a small group of like-minded toxicology researchers, argue now is the time for us to “pause and have an independent scientific committee look at all this new evidence” as “we have a lot of new science specifically about fluoride and the developing brain,” he said.

Critics were buttressed again when a federal court ruled in September that the Environmental Protection Agency (EPA) needed to evaluate fluoride under the Toxic Substances Control Act.

But physicians, dentists and mainstream professional associations from the American Dental Association to the American Academy of Pediatrics stand by recommendations for fluoridated water.

While some towns step away from fluoride, communities such as Buffalo, New York, are restarting programs.

“This is a shame if we don’t take advantage of what we know from the science,” said Koka about the preventive effects of fluoride. “Are there challenges to doing it right? Yes, but should they be so strong they overcome trying at all? That’s a tragedy.”

The CDC has also refined guidance about fluoridation in recent years. In 2015, its water fluoridation recommendations went down to 0.7mg per liter of water, from 0.7 to 1.0mg per liter dependent on climate. Later, the CDC issued a 2019 report that advised parents of children younger than two to speak with their dentist about fluoridated toothpaste, and reminded parents of children younger than three to use only a “grain of rice”-sized “smear”.

As critics argue that federal agencies’ recommendation lag behind, the US government’s National Institutes of Health (NIH) has become one of the chief funders of research into fluoride’s potential impacts on IQ.

“Getting funding from the NIH shows they are interested in this important question,” said Christine Till, an assistant professor at York University in Canada and a co-investigator with Lanphear, whose grant studying tooth dentin and neurodevelopment in Canada was funded by the NIH, but turned down by the Canadian government.

Others, such as Ashley Malin, epidemiology professor at University of Florida, and Dana Goin, assistant professor of epidemiology at Columbia University, have also received NIH funding to research fluoride’s non-dental health effects. Malin is studying fluoride’s impact on children’s sleep and Goin is investigating reproductive health effects.

“There is a lot of ongoing work in this area, particularly in the US,” said Goin. “Hopefully, the results from these studies will help determine whether EPA drinking water regulations and CDC recommendations for water fluoridation are adequately balancing improvements in dental health from fluoridation versus any potential negative effects.”

Goin’s current funding builds on her previous work, which found water fluoridation was not associated with small-for-gestational age or preterm births. She is now exploring whether fluoride is associated with gestational diabetes.

Malin added that it’s a sign of “progress” that the studies can be discussed: “Over a decade ago, to even ask the question of whether optimally fluoridated, or the concentration in drinking water, could be impacting neurodevelopment was quite controversial.”