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On a recent drive through tree-lined neighborhoods in Kinston, water from more than a dozen 5-gallon bottles sloshed around in the back of a white Dodge minivan.
The water was for three families, delivered on a Thursday in January by Dr. Gary Slade, a professor of dentistry at the University of North Carolina at Chapel Hill.
After pulling into the first driveway, Slade lifted the trunk and pulled out a clipboard. He peeled labels from bottle caps and stuck them on a worksheet with identifying numbers and an address. Stacking the bottles on a special dolly, he wheeled them to the door.
“We’ve got water for you,” he announced in his cheery Australian accent, before carrying the bottles inside. He returned empty bottles to the van and recorded them on the worksheet.
Each bottle was assigned to a specific house, although Slade didn’t know if the water inside contained fluoride or not.
Over the next four years, Slade and his research team will deliver roughly 200,000 gallons of water to 200 randomized families in Lenoir and Wayne counties in eastern North Carolina.
The goal of the study? To learn whether naturally fluoridated water from New Bern is statistically better at preventing cavities in young children than water without fluoride.
It seems like an innocuous research question. Yet fluoride in drinking water has been, and continues to be, a contentious topic.
Opponents, including Robert F. Kennedy Jr., the new secretary of the U.S. Department of Health and Human Services, call it a poison. The Fluoride Action Network, a nonprofit dedicated to educating communities about fluoride toxicity, has waged a vigorous campaign in Kinston against the UNC study.
In Union County, southeast of Charlotte, commissioners voted in February 2024 to prohibit the addition of fluoride to community water. In January, Lincoln County commissioners voted not to fix their broken community water fluoridation system, which had been off-line since 2018.
Such actions make fluoride fans cringe. The U.S. Centers for Disease Control and Prevention named fluoridated water one of the 20th century’s 10 greatest public health achievements. The U.S. Department of Health and Human Services (prior to RFK Jr.’s appointment) wanted to expand access to fluoridated water.
But several new reports have reinvigorated the debate about fluoride as a potential neurotoxin—meaning it can hurt the nervous system—and called into question the decades-long assertions of fluoride safety. The reports connect higher levels of fluoride in water with a slight decline in children’s IQ.
These questions are not a reason to panic, nor an open invitation to embrace conspiracy theories. Rather, they show science is an ongoing process, and new discoveries may require adjustments.
And that’s what Slade is trying to do. His waterBEST study is a randomized controlled trial—the gold standard of research—and the type of study both sides of the fluoride debate have wanted for years. He believes this is the first-ever randomized trial of fluoride in drinking water.
But he’s in a tough position.
If fluoride really has detrimental effects on developing brains, then adding it to community water supplies—or in Slade’s case, bringing it to children from a nearby naturally fluoridated community—may be unwise, no matter what lessons are learned.
Chocolate-covered Teeth
To understand why fluoride is both loved and hated requires going back to its discovery in the United States. And that story begins in Colorado.
In 1901, Dr. Frederick McKay moved west to practice dentistry. He set up shop in Colorado Springs and quickly noticed that many residents had what looked like chocolate-covered teeth. McKay recruited others to come study “Colorado Brown Stain,” and after several decades, they identified high levels of naturally occurring fluoride in water as the culprit.
As scientists worked to remove fluoride, they discovered that at lower levels, fluoride actually protected teeth against decay and didn’t cause the brown staining, which they called fluorosis.
This was great news in the late 1930s, as the United States was mobilizing for war. Dental defects like missing teeth, excessive cavities, and poor bites were the leading cause of rejection for military service. Nearly 18 percent of rejections were because the men didn’t have at least 12 teeth. (The average adult has 32.)
“All governmental agencies, federal, state, and local, are becoming more interested in finding means to correct this morbid condition, which today is considered a public health problem,” bemoaned a researcher in 1943, as they proposed adding fluoride to the water.
Yet first, researchers needed to note any negative side effects.
In addition to teeth staining, studies also showed that extremely high fluoride caused rigid bones and joints. But a 1941 study in Illinois involving 117 subjects found no such cases. That, and learning the body excreted most fluoride, left most dental researchers “increasingly optimistic about the possibilities of water fluoridation and … keen on promoting it,” writes Catherine Carstairs, a historian with the University of Guelph in Ontario, Canada, who studies the history of health and illness, including fluoride.
In 1945, Grand Rapids, Michigan, became the first city to add fluoride to its community water, followed by Newburgh, New York. After five years, Newburgh children showed a 60 percent reduction in cavities and a 75 percent decrease in first permanent molar loss, compared with children from nearby Kingston.
These were thrilling numbers. Adding fluoride appeared to be a magic pill against tooth decay. Yet in July 1952, a U.S. House committee investigating chemicals in foods and cosmetics listened to seven days of public hearings on community water fluoridation.
“A minority view is held by a number of qualified scientists, who believe that the safety of this procedure has not yet been sufficiently demonstrated,” the congressional record notes.
“Their position is that there are too many unanswered questions concerning the safety of this procedure to permit recommendations to be made that would result in the consumption of fluoridated water by many millions of people every day of their lives.”
New Questions
U.S. communities kept adding fluoride, and by 1969 nearly 44 percent of the country had access to fluoridated tap water. Today, 73 percent of Americans on community water systems have fluoridated water. In North Carolina, it’s 88 percent.
Fluoride’s early impacts were significant—strengthening tooth enamel and reducing children’s cavities by 50 to 70 percent. Yet over time, the impacts slowed.
By the mid-1980s, children who lived in places with fluoridated water only had 18 percent lower incidents of “decayed, missing, or filled tooth surfaces” compared with children who drank nonfluoridated water, according to a 1999 CDC report.
The reduction was driven in large part by the widespread use of fluoridated toothpaste.
“Early studies of community water fluoridation have shown a clear and important effect on prevention of tooth decay in children,” said Anne-Marie Glenny, a professor of health sciences research at the University of Manchester, UK, and co-author of a highly discussed 2024 review of water fluoridation for preventing cavities. “Recent studies show smaller effects.”
Even with smaller effects, two retrospective studies from 2022 and 2024 show that children in communities that removed fluoride from their water had higher rates of dental procedures after the removal.
But the concerns raised in 1952 never went away. Yes, fluoride could reduce cavities, but was it completely safe? That was less clear.
“The dental community likes to say there’s no risk from low-level fluoride exposure, only benefit,” said Dr. Pamela Den Besten, a professor of orofacial sciences at the University of California, San Francisco, “and I think that’s a problem.”
That sort of overconfidence—heavy on praise for fluoride’s benefits without mention of potential risks—is the result of several factors, said Dr. Steven Levy, a professor of preventive and community dentistry at the University of Iowa College of Dentistry and Dental Clinics and fluoride proponent.
First, it is impossible to prove scientifically that anything is 100 percent safe. Second, unpacking nuanced topics takes time. (Case in point: This article is 3,200 words. Thank you for making it this far.)
And lastly, for dentists working in community health centers or dental clinic shortage areas, engaging in deep research discussions doesn’t feel useful. It’s easier to tell patients fluoride works, which is true, said Levy, even if it’s not the full story.
But “this is safe—trust us,” messaging can damage public trust when scientific advancements lead to new recommendations, said Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in British Columbia, Canada, and a leading voice for more fluoride research.
“It’s not that people were wrong in the past and we’re right today,” he said. “Science evolves, and we have to keep up with those changes. People need to be humble enough to look at the new evidence on behalf of children’s health.”
This new research points to a potential link between fluoride exposure and IQ loss in children, though at exposure levels higher than most Americans receive from their tap water.
After reviewing more than 100 studies, researchers at the Research Triangle Park-based National Toxicology Program concluded with moderate confidence that exposure to fluoride at levels above 1.5 milligrams per liter (mg/L) is associated with slightly lower IQ in children.
The study could not comment on any IQ impacts at 0.7 mg/L—the recommended level of fluoride in U.S. water. Slade’s study water level has naturally occurring fluoride levels of 0.8.
A related analysis, published in the Journal of the American Medical Association (JAMA) Pediatrics medical journal in early January, found that for every 1 mg/L increase of fluoride in children’s urine, IQ dropped by 1.63 points.
“Science evolves, and we have to keep up with those changes. People need to be humble enough to look at the new evidence on behalf of children’s health.”
Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University
While a difference of four IQ points would not be noticeable at an individual level, a four-point decrease across the country could mean roughly a million more U.S. children classified as intellectually challenged, said Christine Till, a clinical neuropsychologist and professor of psychology at York University in Toronto, Canada, who studies environmental toxicants on children’s development.
The American Dental Association reconfirmed its support for fluoridated water and criticized the National Toxicology Program work for reviewing poor-quality, non-U.S. studies. (The U.S. has no studies on fluoride and IQ in children, and of the 74 studies, 22 were considered high quality.) The Association also emphasized that the reports “did not find any connection between lower IQ and fluoride intake at the level recommended for community water fluoridation.”
Yet fixating on that 0.7 number is short-sighted, said Kyla W. Taylor, health scientist and lead author of the recent reports. She’s worried about all the other places where infants, children, and pregnant women get fluoride beyond the tap, pushing their total exposure levels higher.
Besides tap water, we also get fluoride from food. Black tea, seafood, and grapes absorb fluoride from soil, water, or pesticides, and other foods and drinks may be made with fluoridated water. The U.S. Environmental Protection Agency says adults get about 2.9 mg of fluoride per day from food and fluoridated water, while children under 4 get 1.2 to 1.6 mg/day.
Even though we excrete fluoride fairly quickly, there are signs Americans may still be getting too much. White spots or lines on our teeth are evidence of dental fluorosis. Due to increasing rates of fluorosis, in 2015 the U.S. Public Health Service lowered the recommended fluoride levels in drinking water from 1.2 mg/L to 0.7 mg/L.
That cosmetic-driven change was relatively easy to communicate, said John Bucher, a former senior scientist with the National Toxicology Program who studied fluoride over four decades.
But fluoride’s “developmental, neurological effects are not ones that you can see and feel,” he said. “It’s a silent hazard, and it’s more problematic for people to wrap their hands around.”
Choosing Kinston
Thirty years ago, Slade, the UNC-Chapel Hill professor, remembers standing up in conferences of the International Association for Dental Research and asking his peers: “Why has no one done a randomized-controlled trial on fluoride’s ability to prevent cavities?” He was tired of critics pointing out the absence.
His colleagues said fluoride as a public water system intervention was “impossible to randomize,” and that “you don’t do randomized trials on things that you know work.”
But, as a professor of evidence-based dentistry, Slade wanted the data. So five years ago, despite the naysayers—and his own self-doubt that it was too much work and that at 65, he was getting old—he submitted a grant application to the National Institutes of Health.
“Maybe I’m just pigheaded or whatever,” he said with a chuckle, “but I’ve always said this is doable.”
In the Water from Bottles to Establish Strong Teeth (waterBEST) study, Slade proposed to deliver bottled water to the homes of 200 children, enrolled between the ages of 2 months and 6 months old.
Half the families would get naturally fluoridated water from New Bern, the other half, nonfluoridated water from Kinston.
For 3 and a half years, the children’s water source would be study water, except when making baby formula. (Slade’s team would bring study families extra nonfluoridated water for that purpose to avoid fluoride overexposure.)
Each child would get a quarterly health check and a yearly dental screening, and have their fingernail and toenail clippings collected annually so researchers could check for biomarkers of fluoride. The end point would be a full dental exam around the child’s fourth birthday.
Enrolled families would receive a freestanding water dispenser, age-appropriate bottles and sippy cups, and up to $480 for full participation, paid in annual increments.
If all went as planned, families would stay enrolled, the study would run smoothly, and Slade would finally have strong scientific evidence of fluoride’s ability to prevent tooth decay. This study will not look at impacts on neurotoxicity or IQ.
In 2019, Slade brought his idea to Kinston community leaders, including Lenoir County Health Director Pamela Brown.
Slade explained that Kinston, population 19,400, was one of the biggest population centers in North Carolina that has never had fluoridated water. And as a city, not a sparsely populated county, it made frequent bottle deliveries feasible.
Brown said she was immediately drawn to the idea that Kinston residents could meaningfully contribute to science, and she remains an ardent study supporter.
Slade spent the first year of the grant engaging with Brown and other trusted figures in the community. He wanted to fend off concerns that he and his team were “white-coated researchers driving into town to answer scientific questions with whomever they could pick off the streets.”
Opposition Surfaces
With the support of community leaders, Slade began enrolling families. But by 2022, opposition flared. For every letter Slade mailed to a new parent, the Fluoride Action Network mailed one, too, accusing researchers of experimenting on babies and claiming researchers weren’t giving parents full information.
“What the study employees are not telling you is that there is rapidly accumulating scientific evidence that the fluoride in the study water can damage the developing brains of young children,” read the letter, signed by Paul Connett, one of the network’s founders. “Over 70 scientific studies have now found that fluoride in early childhood can lower IQ or increase risk of ADHD.”
That letter, along with a digital billboard the group rented near the hospital featuring two rotating images proclaiming, “Don’t Experiment on Kinston Kids,” immediately sparked fear.
In September 2022, the Kinston/Lenoir County NAACP hosted a community forum in Kinston’s Emmanuel Hill Memorial Free Will Baptist Church Fellowship Hall. Residents asked how the Black community could trust this study and if other things were being added to the water.
Slade explained the study and invited residents to tour the Kinston bottling facility. He explained they only purify the water; they don’t add anything. Slade answered subsequent questions on his website.
Stuart Cooper, executive director of the Fluoride Action Network, called into the meeting from out of state. He expressed concerns that the parental consent form did not mention dental fluorosis or neurotoxicity; it only listed the vague risks of “too much fluoride intake” and skin being nicked during nail trimming. The form was updated in 2022 to mention dental fluorosis.
There’s also no guidance for enrolled families if the mother becomes pregnant again during the study. Studies have also linked higher maternal fluoride exposure to lower IQ in children.
The Fluoride Action Network “does not oppose the use of fluoride toothpaste, mouthwashes, other dental products,” Cooper told The Assembly. “We oppose water fluoridation and ingestion. … We try to alert the public to fluoride toxicity situations where they will be overexposed.”
After the National Toxicology Program report came out last year, Slade went to UNC-CH’s research ethics committee. Did they believe it altered the potential risks to study participants? (The program notes in bold on its website that “there were insufficient data to determine if the low fluoride level of 0.7 mg/L currently recommended for U.S. community water supplies has a negative effect on children’s IQ.”) Slade’s water is 0.8 mg/L. The ethics committee said no, Slade said.
Fluoride may be a complex issue, said health director Brown, but discussing it shouldn’t be driven by fear. That’s why she was so frustrated by the opposition.
“You don’t have to have a PhD to have your child’s best interests in mind. You don’t have to have a master’s degree to understand a consent form.”
Pamela Brown, Lenoir County health director
If the study’s naturally fluoridated water—which is trucked in from New Bern and then bottled—is so dangerous for Kinston children, what about New Bern children who drink it every day? What are New Bern parents supposed to think?
She said opponents implied Slade was preying on Kinston because the community is 66 percent Black and Lenoir County is high on the social vulnerability index. Nearly one-third of county residents receive food stamps or SNAP assistance, and one in five households are below the federal poverty level.
“You don’t have to have a PhD to have your child’s best interests in mind,” Brown said. “You don’t have to have a master’s degree to understand a consent form. I felt as if [opponents] were trying to steal something from this community rather than the community being able to say, ‘This is not for us.’”
However, some parents declined. Slade had to expand to neighboring Wayne County to enroll 200 families.
But the billboard is gone. It was expensive, Cooper said, and FAN is a small nonprofit. It maintains a website and opts for online advertising and local word of mouth to share its concerns.
It hasn’t deterred Slade. He delivers water to Kinston families several times a month in between his classes in Chapel Hill.
“Reasonable people are agreeing we need more evidence,” Slade said. “We certainly need more evidence on neurotoxicity sort of concerns, way more evidence. And I say we need evidence [from a] randomized trial, too. That’s not the only evidence that we need, but that will be compelling evidence.”
In a Q&A on the NIH website with Jennifer Webster-Cyriaque, deputy director of the National Institute of Dental and Craniofacial Research, she noted: “We need more studies to better understand potential risks and benefits of higher levels of fluoride. NIH is planning additional studies along these lines.”
But gathering evidence takes time. Slade won’t have final results for another four or five years. That does little to calm today’s debate or influence people who already consider the fluoride question settled, for good or ill.
“We don’t cater to people whose minds are closed,” Slade said. “But science does try to serve the purpose of furnishing the evidence for people who want to look.”
Sara Israelsen-Hartley, a journalist with a master’s degree in public policy, lives in Raleigh with her family. Read more of her work here.