Brigham City, Utah—After turning off Utah State Route 90 and making a short drive down Power Plant Road at the foot of the rugged Wellsville Mountains, Mike Waite pulls up in front of a beige storage shed. “This is what used to be our fluoride building,” says Waite, Brigham City’s assistant public works director and water superintendent.
The shed’s interior is mostly empty. Two sheets of paper with information about safety operating procedures for water fluoridation and emergency contacts remain taped to a wall. Anchor bolts once used to secure two 2.75 m tall tanks that stored fluorosilicic acid—a colorless, corrosive liquid added in small amounts to fluoridate drinking water—stick out of the bare floor. Ring stains, about 2 m in diameter, left behind by the tanks blemish the gray-speckled floor tiles. The discarded tanks sit in a container outside, waiting to be hauled away.
The city—about an hour north of Salt Lake City with a population of about 20,000—had been adding fluoride to its drinking water since 1965. Residents had voted in favor of doing so to reduce tooth decay. They voted again, in 2023, to keep fluoride in the water. But earlier this year, Utah became the first state to ban the addition of fluoride to its public drinking-water systems.
Governor Spencer Cox signed H.B.81, the controversial state bill, into law on March 27, pulling the plug on the fluoridated water that was being received by 44% of Utah’s population. He compared community water fluoridation to being “medicated by [the] government.” After the policy took effect, Brigham City disconnected all fluoridation-related piping on May 8 and had removed its fluorosilicic acid tanks by June 2.
The ban drew sharp opposition from dental associations and several public health officials. But Robert F. Kennedy Jr., secretary of the US Department of Health and Human Services, praised Utah’s decision. In 2024, he had vowed to remove fluoride from US drinking-water systems. He claimed on X that the added fluoride is associated with several health risks, including bone cancer and impaired cognitive development in young children. Some of those claims were unsubstantiated, and others lacked the dose-dependent context. During an April 30 cabinet meeting, Kennedy contended that “the more [fluoride] you get, the stupider you are.” But the link between fluoride intake and kids’ cognitive abilities remains highly debated among scientists, particularly at the low water fluoridation level, 0.7 mg/L, that the CDC recommends for good oral health.
Amid the tangle of research bias, conflicting results, and policy changes, scientists want to ensure that any real risks of using fluoride are contained. But there’s also danger in discounting fluoride’s proven health benefits while centering unclear, poorly understood risks—a move that could spike rates of tooth decay and cost the US billions of dollars in dental care.
Fluoride in flux
Almost all water naturally has fluoride ions in it that originate from fluoride-bearing minerals in regional rocks. The city of Seagraves in Texas receives water with 4.86 mg/L of naturally occurring fluoride; in Morrisville, Illinois, the groundwater fluoride concentration is 6.79 mg/L; in Jacksonville, Florida, the levels range between 0.385 and 1.22 mg/L.
But Brigham City’s water largely lacks any natural fluoride. “It’s nondetectable,” Waite says. “All the fluoride that was present in the water was added [to reach the CDC-recommended level].”
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The city’s mayor, DJ Bott, supported the ban (PDF), citing costs of about $80,000–$100,000 per year to fluoridate water that’s used mostly for purposes other than drinking. Some Brigham City residents are embracing access to water that’s largely fluoride-free, but many others are angry.
The state’s decision to override the wishes of the city’s majority voters, and its own law requiring such a vote to make any local fluoridation-related changes, “really made us mad,” says 73-year-old Teresa Moore. “They [the legislators] should have listened more to the medical professionals than the political advocates.” Local dentists are now bracing for an uptick in cavities in the coming years, particularly among people from low-income communities who may not get regular dental checkups or prioritize the purchase of fluoride-containing dental products.
Another big concern is the US Food and Drug Administration’s plan to pull ingestible fluoride supplements, which dentists and pediatricians prescribe to kids living in low- or no-fluoride areas, from the market. Although these products have been used for decades, they haven’t been reviewed or approved by the FDA.
In its announcement of the plan, the FDA suggested multiple health concerns, including the idea that ingested fluoride can alter the gut microbiome—although current research indicates limited impact at low fluoride levels. The agency says it will be conducting a safety review of fluoride drops and tablets but already indicated its plan to remove these products from the market upon completing the review. The announcement also cited other health concerns, including “possibly decreased IQ.”
Meanwhile, Florida has followed Utah and banned municipal water fluoridation. Massachusetts is considering doing the same. Kentucky wants to make the practice optional. And Louisiana is contemplating replacing its mandatory water fluoridation rule with a process that would allow communities to make their own decisions—via local elections—on the issue.
In April, the US Environmental Protection Agency also announced that it was expeditiously reviewing new science on fluoride in drinking water—prompted by a federal district court judge’s order—and would revise its agency standards if needed. The basis for action is a controversial 2024 report that concluded with “moderate confidence” that exposure to fluoride levels exceeding 1.5 mg/L was associated with lower IQ in children. The report’s authors—government scientists at the US National Institutes of Health’s National Toxicology Program (NTP)—also said that more studies were needed to fully assess any neurotoxicity at lower fluoride levels.
In recently published work, some scientists found no association between low-level fluoride exposures and kids’ IQ, while others noted a slight decline in IQ.
A further complication is that “there is no clear mechanism by which fluoride can impact IQ,” says John Fawell, a visiting professor at Cranfield University who’s advised the World Health Organization on water quality standards. But given what’s known from recent research, “there is no need to panic,” he says. Fawell thinks that artificial fluoridation “deserves a proper, objective reassessment that covers all sides [risks and benefits] of it.” And, he says, those deliberations shouldn’t distort discussions on health concerns in areas that receive water with naturally high fluoride levels.
The fight over fluoridation
In the early 1900s, dentists Frederick McKay and Greene Vardiman Black began investigating a phenomenon called “Colorado brown stain.” Most of the children born in Colorado Springs developed teeth with brown or mottled discoloration but had surprisingly low rates of dental decay. Later work pointed to extremely elevated fluoride levels in Colorado Springs and other regions where this condition, termed dental fluorosis, was prevalent.
Ingesting too much fluoride can cause mottling, staining, and sometimes pitting of teeth, and if fluoride intake is more excessive, skeletal fluorosis can occur, leading to weaker bones.
But Trendley Dean, the first dental scientist at the NIH in 1931, didn’t see such fluorosis when water fluoride levels were 1 mg/L or lower. And at that concentration, fluoride in drinking water could still reduce dental caries. Suggestions to add fluoride to water to prevent tooth decay emerged (PDF).
Daily exposure to small amounts of fluoride, especially during the formative years when teeth are developing, can reduce the risk of caries and decay. Fluoride combines with hydroxyapatite, the main component of tooth enamel, to form enamel-strengthening fluorapatite, says James Bekker, a pediatric dentist at the University of Utah. Fluoride can also help reduce acid production by plaque-causing bacteria and replace minerals lost from teeth during decay.
In 1945, Grand Rapids, Michigan, became the first city to fluoridate its municipal water to the 1 mg/L concentration. Ten years later, a study noted a nearly 60% reduction in dental caries among children born after fluoride had been added to the drinking water. More towns and cities opted for fluoridated water, but not without opposition and battles at town hall meetings.
“The idea that people shouldn’t be putting things in water that are potentially a drug . . . that’s always been part of the issue,” says John Bucher, a senior scientist who retired from the NTP in 2021 and coauthored the agency’s 2024 report. Over the years, other concerns have mounted.
In 1990, Bucher and his colleagues showed that 4 of 130 male rats given drinking water with extremely high doses (100 and 175 mg/L) of sodium fluoride for 2 years developed bone tumors “That prompted some evaluations of potential for bone tumors in humans—in children, in boys primarily—which were inconclusive or negative,” he says. Thereafter, several studies, many from China, reported moderately lower IQ scores among children in areas with naturally high fluoride concentrations in drinking water compared with those living in low-fluoride regions.
The fluoride levels in these studies are “usually 2.5 to 15 times higher than we have in the water,” says Johnny Johnson, president of the American Fluoridation Society. “The opponents latched on to that.”
In 2012, researchers from Massachusetts and China who reviewed 27 studies—25 of which were from China—on fluoride exposure and IQ scores pointed to several limitations, such as missing information and methodological issues. They inferred that the studies’ results do not offer clear evidence of risk from water fluoridated at the low levels that are typical in the US but also do not show an absence of risk (PDF).
In 2015, the US Public Health Service updated its fluoride recommendation to 0.7 mg/L from its previously suggested range of 0.7–1.2 mg/L. This shift stemmed from the need to balance the risks of fluorosis with cavity control and the use of other sources of fluoride such as oral care products.
Using fluoride toothpaste boosts the amount of fluoride in the mouth temporarily but dramatically, Johnson says. That’s different from the lower background level delivered by fluoridated water throughout the day. “It’s those combinations of things that help give you less cavities,” he adds.
Given this combined advantage, scientists have found that the dental benefits of water fluoridation alone are lower than they used to be. While the CDC cites research indicating a nearly 25% reduction in cavities in adults and children that’s attributable to community water fluoridation, a recent review from researchers in the UK estimated that reduction to be less than 4% in kids. But the review couldn’t determine if and how discontinuing water fluoridation would affect children’s dental health.
Lindsay McLaren studied exactly that issue in Calgary, Alberta, a city that stopped fluoridating its water in 2011. After about 7 years, she and her colleagues found that 65% of nearly 2,600 second-grade students that she and her colleagues surveyed had at least one cavity compared with 55% in the neighboring water-fluoridated city of Edmonton. After accounting for several contributing factors, “the only thing that was left as a reasonable explanation was the fluoride in the water,” says McLaren, a professor of community health sciences at the University of Calgary. The city restored artificial fluoridation this June.
The vote
In Brigham City, water fluoridation had largely been a nonissue since the 1965 vote. But on March 16, 2023, Brigham City council members voted 3–2 to put the question of discontinuing water fluoridation—Proposition 3—on the ballot, largely because of concerns about costs.
Once on the ballot, Prop. 3 became “such a hot-button issue,” says Loni Newby, assistant editor at the Box Elder News Journal, a locally owned newspaper.
Letters to the editor trickled in. One challenged the need for community water fluoridation, given that many toothpastes and mouthwashes on the market contain fluoride. Another expressed concerns about ingesting too much fluoride. Dentists flagged the benefits of water fluoridation at an optimal level and the CDC’s recognition of the practice as one of the 10 greatest public health achievements of the 20th century.
At a city council meeting, local orthodontist Steven Blanchard said removing fluoride was “a big mistake.” Clark Andersen, an orthodontist who practices both in Brigham City and the nearby non-water-fluoridating city of Tremonton, said that most of the time, he could look in a young child’s mouth and tell if they lived in an area that lacked fluoride in municipal water. “It’s not like kids in Brigham City don’t ever get cavities, but the amount and the severity of decay in kids from those other [non-fluoridated] areas is dramatic,” Andersen told C&EN.
In the November 2023 election, 67% of the city’s 3,491 voters favored keeping fluoride in the city’s water.
But when Utah legislators began discussions about a statewide water-fluoridation ban, and some described it as “forced medication,” “I was shocked,” says Brigham City council member Robin Troxell, who has previously served as the tribal health administrator for the Northwestern Band of the Shoshone Nation. “I’m just saddened that things that are actually not political have become political,” she adds.
When the ban when into effect, Utah updated its law to allow pharmacists, in addition to dentists and pediatricians, to also prescribe ingestible fluoride supplements. But these supplements aren’t likely to be as effective as water fluoridation, in part because children must take the pills daily, and such compliance is challenging.
The state’s fluoridation ban left Brigham City resident Patricia Saddler, age 58, angry. “Some hard work was really put into making a difference for our youth and our children,” she says. “Why take that away? It’s a real shame.” But resident Shelly Hutchings, age 48, was concerned that she and her kids might be ingesting fluoride at potentially harmful levels, from water, from toothpaste, and from common foods and beverages, including fruits, seafood, tea, and coffee.
EPA estimates suggest that drinking water accounts for 40–70% of a person’s total fluoride intake. That’s supplemented by fluoride-containing beverages and food they may consume.
A man weighing about 70 kg, for example, would need to drink nearly 450 L of water fluoridated at 0.7 mg/L to experience acute fluoride toxicity. But scientists don’t quite know the level at which “we begin to see potential effects on neurodevelopment,” Kyla Taylor, an epidemiologist at the National Institute of Environmental Health Sciences and coauthor of the 2024 NTP report, tells C&EN via email.
The IQ conundrum
Recently, researchers have been assessing the effects of fluoride exposure during pregnancy on kids’ full-scale IQ, a measure of global intellectual functioning. Instead of using concentrations of fluoride in water to determine exposure, the research teams measured fluoride in urine samples to account for its intake from water and other sources. “Because the fetal and developing brain is especially sensitive to neurotoxicants, there is concern that pregnant women, infants, and young children may be receiving more fluoride than necessary,” Taylor says.
In Mexico City, where residents rely on fluoridated table salt instead of water fluoridation to reduce dental caries, researchers found that higher prenatal exposure to fluoride was associated with lower IQ among 6- to 12-year-olds. But the study authors, making estimates based on urinary fluoride levels, noted that “there was some evidence that associations with IQ may have been limited to exposures above 0.8mg/L.”
In two studies spanning six major Canadian cities—some that fluoridate drinking water and others that don’t—researchers found a roughly 2-point decline in full-scale IQ among 3- to 4-year-old boys with every 0.5 mg/L increase in fluoride levels in the gestational parent’s urine during pregnancy. They didn’t see a similar statistically significant association among girls.
A drop of a couple of IQ points may seem small, says Christine Till, a professor of psychology at York University in Toronto and coauthor of the studies. But “if we shift the entire population down by, let’s say, 1.5–2 IQ points, that would increase the number of children falling in the intellectually challenged range and, on the other side of the curve, decrease the number of children falling in the gifted range.”
Still, other studies have failed to find such associations.
In a recent review of 74 studies assessing pre- or postnatal fluoride exposure and children’s IQ scores, Taylor, Bucher and their colleagues identified only a handful of studies that had a low risk of bias and looked at fluoride levels below 1.5 mg/L in water or urine. A meta-analysis of those studies revealed a slight decline in IQ when researchers estimated exposure using urinary fluoride levels but no significant change in IQ when they used drinking-water fluoride concentrations. NTP’s summary of this meta-analysis noted 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.” The NTP authors also added that the “meta-analysis was not designed to address the broader public health implications of water fluoridation in the United States.”
Still, the Trump administration’s recent Make America Healthy Again reportcited the results of this meta-analysis to flag fluoride as a potential source of concern for children’s health.
But in the past, several scientists have sounded caution regarding the analysis and interpretation of Taylor, Bucher, and their colleagues’ study and the NTP report. They’ve also pointed to another recent meta-analysis that did not find an association between the fluoride levels used for community water fluoridation and lower IQ in kids.
For the most part, critiques have flagged the use of spot urine measurements made from a one-time sample as opposed to multiple samples collected over 24 h to estimate fluoride exposure. They’ve called the measurements “invalid.” Fluoride’s short half-life in urine means those levels fluctuate throughout the day, depending on recent food and water intake. Some studies relied on one or two spot urine tests, while Till and her colleagues averaged the values of three spot urine samples—one from each trimester.
While Till agrees that spot urine tests “are not a perfect measure of fluoride intake,” she thinks they have value. Till argues that the EPA routinely relies on urinary levels of heavy metals or persistent organic pollutants, suggesting that urinary fluoride concentrations would also be a reliable biomarker of exposure. She also says that researchers on her team noted a similar decline in IQ when they estimated fluoride intake based on how much tap water, coffee, and tea the pregnant people said they consumed daily.
Bucher, too, disagrees with the argument that spot urine tests are invalid. As opposed to doing individual assessments, “when you do [these tests] on the population level, there’s information that’s significant,” he says.
Steven Levy, a professor of preventive and community dentistry at the University of Iowa, thinks blood fluoride levels may provide a more accurate assessment of short-term fluoride exposure than spot urine tests. But citing the US National Research Council Framework, the EPA contended, in a response to a 2017 petition concerning water fluoridation, that urinary and blood fluoride levels may be “useless” for risk-assessment purposes. Some researchers, including Till, are measuring fluoride in kids’ toenail clippings and shed baby teeth to try and estimate long-term exposure levels.
Meanwhile, Levy and several others disagree with Till’s recommendation for people to reduce their fluoride intake during pregnancy, as a precautionary step until more studies are done. But Levy says the evidence for the impact of prenatal fluoride exposure on kids’ IQ at community fluoridation levels is not nearly clear enough to make public health recommendations.
Back in Brigham City, dentists feel like they may be left with fewer options to offer parents who still want to access fluoride for their children’s dental care. With the FDA’s plans to pull prescription fluoride supplements from the market, “I just kind of have to shrug my shoulders and say [to parents], You know what, I’m really not sure what’s going to happen,” says Randell Capener, a dentist in Brigham City.