Communities across Florida in recent months have taken up the question of whether to fluoridate water supplies. This month, Melbourne joined a growing list of jurisdictions voting to end fluoridation.
More than 70% of Floridians who get water from community water systems receive fluoridated water, per the Florida Department of Health, and more communities are expected to take up the issue.
But what does it mean to fluoridate water? How long has the practice been around? And why does adding fluoride to water concern some people?
What is fluoride?
Fluoride is a naturally occurring mineral found in groundwater, soil, rivers and lakes, according to the National Library of Medicine.
In the United States, nearly 11% of domestic wells pump water with fluoride concentrations above 0.7 parts per million, the level recommended for drinking water, per a 2020 analysis by the U.S. Geological Survey. One way to envision 0.7 ppm: It’s like a little less than 1 minute every two years, according to one analogy (0.7 ppm is the same as 0.7 milligrams per liter, or 0.7 mg/L) .
Cognitive impacts are associated with higher fluoride exposures starting at 1.5 ppm, a little more than twice the 0.7 ppm rrecommendation, according to a review of some recent studies.
Why do we fluoridate?
Community water fluoridation is the act of adjusting fluoride amounts in drinking water to a level recommended for cavity prevention, according to the Centers for Disease Control and Prevention.
Evidence shows that fluoride can prevent and even reverse early tooth decay, according to the National Institutes of Health. The road to that understanding begins in 1901, when a dentist in Colorado Springs began noting brown stains on residents' teeth. However, what interested scientists was that people with brown stains were also found to be resistant to tooth decay. Decades later, researchers found that the water contained high concentrations of fluoride, which was determined to be responsible for the brown stains and resistance to decay.
In 1945, the first large-scale study of fluoridating water was conducted in Grand Rapids, Michigan. After 11 years of observing school children, researchers found a 60% drop in the rate of tooth decay. As a result, fluoridation projects began popping up across the country. Today, water fluoridation projects affect 200 million Americans, according to the National Institute of Dental and Craniofacial Research.
Why do some people want to end community fluoridation?
For as long as fluoridation has been going on, there have been skeptics suggesting other harmful effects of fluoride. Through the decades, fluoridation has been heralded by a majority in the scientific community.
However, President Donald Trump's pick for Health and Human Services secretary, Robert F. Kennedy Jr., is anti-fluoride and has talked about ending fluoridation, sparking renewed attention on the subject.
“That caused a ripple effect,” said Justin Harvey, a Maitland resident who says he started raising concerns to local community leaders about fluoride seven years ago. “We've had commissioners say, solely based on that, that is good enough reason for us to take it out.”
At the end of 2024, Florida Surgeon General Dr. Joseph Ladapo issued new guidance, discouraging local governments from fluoridating water and going as far as to call it “public health malpractice.” The guidance mentions a number of concerns outlined by studies, including associations of fluoride exposure with attention-deficit/hyperactivity disorder and diminished impulse control in children, as well as reduced IQ.
Those associations are identified in some newly published science from the National Institutes of Health’s National Toxicology Program: a meta-analysis, or systematic review, of existing epidemiological studies on fluoride exposure’s potential cognitive impacts on children.
The new science is what a federal judge recently relied upon in his ruling in favor of an anti-fluoridation coalition, which sued the EPA in 2017. Now, the EPA must reevaluate its maximum standards for fluoride and the science behind those standards, per the ruling.
The ruling also took issue with the EPA’s safety margin for fluoride. In its risk assessment process for chemicals, the EPA establishes a safety margin: a gap between each chemical’s maximum exposure level and hazard level, or the point at which known risks appear. The agency’s default safety margin is typically 10, meaning the chemical is assigned a maximum exposure level 10 times lower than the hazard level.
For fluoridation, though, the safety margin is only twice as high as the recommended 0.7 ppm. At the same time, the toxicology program has found fluoride levels of 1.5 ppm — about twice the recommended amount — to have some associations with negative cognitive outcomes.
The new science informing the court ruling is compelling but has limitations. Most of the studies (52 of 74) in the meta-analysis were deemed low-quality, meaning they had a high risk of bias. Also, the studies didn’t use the same methodology: some measured fluoride concentrations in drinking water, but others measured urine samples. Most of the studies reviewed were from China, and none from the United States.
That said, zooming into the handful of high-quality studies in the toxicology review, almost all of those studies found associations between estimated fluoride exposure in children and either reduced IQ or other types of adverse cognitive or neurodevelopmental outcomes.
Fluoride could be harmful, depending on the amount of exposure. That meta-analysis found that for every 1.0 ppm increase in urinary fluoride, there is a decrease of 1.63 IQ points in children.
What do — and don’t — studies tell us about the harms of fluoride?
Much more research would be necessary to establish whether fluoridated drinking water is a primary cause of the cognitive effects observed by some studies — especially because many other factors are known to contribute to those impacts.
One study co-authored by a University of Florida researcher is the first of its kind in the U.S. to examine how prenatal fluoride exposure might impact child neurobehavior, according to assistant professor of epidemiology Ashley Malin. The study’s findings are consistent with those from similar studies based in Canada and Mexico.
“We found that higher exposure to fluoride during pregnancy was associated with more neurobehavioral problems in the children by age 3,” Malin said.
Malin’s study found prenatal fluoride exposures of 1.2 ppm and above were associated with an increased risk of neurobehavioral problems, including ADHD. It did not consider IQ levels.
How much fluoride are we actually adding to water?
HHS recommends a 0.7 ppm concentration of fluoride for drinking water, which is what water utilities typically add.
Meanwhile, the EPA’s enforceable limit for fluoride is 4.0 ppm, meaning that’s the maximum amount allowed in public water systems. The EPA also requires systems to notify customers if average fluoride in water levels exceed 2.0 ppm.
With dentistry developments over the years, is fluoridation necessary?
Most dentists say yes.
Cavities are a big deal. They’re infections that lead straight to the bloodstream. Studies show that in extreme cases cavities can cause cardiac arrest, heart disease or even a stroke.
“Fluoridated water will slow (cavities) down,” said Dr. Johnny Johnson, president of the American Fluoridation Society and a pediatric dentist. “You will have a lot less cavities and less severe cavities. And through what you're doing, good hygiene, having fluoride in your water, using a fluoridated toothpaste, those are complementary.”
Fluoridated water reduces cavities by 25% in children and adults, according to the CDC. Studies have also shown children living in fluoridated communities have fewer decayed teeth compared those in nonfluoridated communities.
According to the CDC, fluoridation is the most cost-effective way of supplying dental care across all communities regardless of age, education and income levels.
What the new science does say
A “statistically significant association between higher fluoride exposure and lower children's IQ scores, showing that the more fluoride a child is exposed to, the more likely that child's IQ will be lower than if they were not exposed,” is perhaps the most compelling finding from the meta-analysis.
The authors wrote their review finds, “with moderate confidence, that higher estimated fluoride exposures” — specifically, at concentrations above 1.5 ppm — “are consistently associated with lower IQ in children.”
What it doesn’t say
The meta-analysis is definitive in that its findings are not definitive on fluoride’s effects: “More studies are needed to fully understand the potential for lower fluoride exposure to affect children’s IQ.”
And it’s key to remember, the associations found by the studies were at concentrations well above the recommended 0.7 ppm.
“There were not enough data to determine if 0.7 mg/L of fluoride exposure in drinking water affected children’s IQ,” according to JAMA’s meta-analysis.
Also, “there were few studies, and therefore uncertainty, in the relationship below 1.5 mg/L when fluoride was measured only in drinking water.”
Remember, the studies were based in a mix of two approaches: They measured fluoride concentrations in urine or drinking water.
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