Most communities in the U.S. add fluoride to the tap water. It has been common practice for nearly 80 years to protect against tooth decay and cavities, and it's considered a major achievement in public health. The Centers for Disease Control and Prevention says research shows that community water fluoridation reduces cavities by around 25%.
It has also long drawn opponents who have raised concerns about the practice, ranging from evidence-based concerns to unsubstantiated conspiracy theories. The debate heated up recently when President-elect Donald Trump picked Robert F. Kennedy Jr. to lead the Department of Health and Human Services. Kennedy is a longtime anti-vaccine activist who has also been outspoken in opposing water fluoridation, and if he's confirmed in the role, he could influence policy.
This week, government scientists published a paper in the medical journal JAMA Pediatrics that has added to the debate. It is the analysis behind a 300-page report released last August from the National Toxicology Program, part of the National Institutes of Health.
That report concluded with "moderate confidence" that there may be a link between high levels of fluoride exposure and lowered IQ. This could indicate possible neurodevelopmental harms to pregnant people or young children, when they are exposed to drinking water containing at least 1.5 milligrams of fluoride per liter — a level more than twice what's recommended (0.7 mg/L) for the U.S. water supply.
Monday's analysis digs deeper into the data behind these conclusions. It looks at a few dozen foreign studies that other researchers have conducted, mostly in China and India, and finds an association between high levels of fluoride and a small decrease in children's IQ.
"There were not enough data to determine if 0.7 mg/L of fluoride exposure in drinking water affected children's IQ," Christine Flowers, director of the Office of Communication at the National Institutes of Health, wrote in an email.
While the conclusions are consistent with the August report, the timing of the paper, released weeks before Trump takes office, gives it renewed prominence. The report's contents were given "substantial weight" in a recent federal court ruling that ordered the Environmental Protection Agency to address potential risks posed by fluoride levels.
The analysis is controversial. The paper was published alongside two editorials in JAMA Pediatrics. One, by Steven Levy, a public health dentist at the University of Iowa, questioned the analysis's methods and disagreed with its conclusions. The other, by a trio of children's health researchers, supported its findings.
Using this analysis — which is inconclusive at levels of fluoridation below 1.5 mg/L — to inform the debate over low levels of fluoride in drinking water feels like a stretch to fluoridation supporters like Levy.
"The major problem is that the science is not as strong as it's presented by these authors," he says. For instance, the study authors write in the paper's abstract that fluoride exposure seems linked (in certain studies) with lower IQ at levels even below 1.5 mg/L, but Levy notes that the data they provide aren't conclusive.
Also, Levy says the authors didn't fully consider some recent research that casts doubt on the links between fluoride exposure and IQ. He says there's sometimes a pattern in public health research in which some initial studies suggest a problem, but over time, as the problem gets better studied, "the evidence goes in a somewhat different direction." He points out that some of the more recent fluoride studies, which he thinks are better designed, found no negative effect on IQ, and he thinks they should have been given more weight in the recent analysis.
To others, the analysis published this week makes a strong enough case out of imperfect evidence for action. "What the study does, or should do, is shift the burden of proof," says Dr. Bruce Lanphear, a children's health researcher at Simon Fraser University, who co-authored the other editorial, which supported the paper's findings. "The people who are proposing fluoridation need to now prove it's safe."
Lanphear agrees with concerns, raised by the study authors, that the base level of fluoridation, plus the myriad other sources of fluoride in people's lives — such as toothpaste, mouthwash, and food and drinks, including some teas, fruits, vegetables and seafoods — could be pushing fluoride to harmful levels in some vulnerable people.
"There is concern that pregnant women and children are getting fluoride from many sources … and that their total fluoride exposure is too high and may affect fetal, infant, and child neurodevelopment," wrote the NIH's Flowers.
And while water fluoridation does clearly prevent cavities, Lanphear says the relative benefits have declined in the past few decades since people started using fluoridated toothpaste, a point supported by a recent analysis by U.K. researchers.
"There are other ways we can protect children from developing cavities," he says. "We could, for example, regulate sugary beverages … [or] have programs to help children learn to brush their teeth more effectively."
It's time to reassess the potential risks of fluoride against its benefits, Lanphear says.
Those benefits are substantial and so common that they're taken for granted, says Levy. But "it isn't that cavities are under control for everyone," he says. Fluoridated water most benefits those who are poor and underserved, who might not have fluoridated toothpaste or regular access to dental care.
And while cavities can be prevented in other ways, "those alternatives are for much more costly things," Levy says. "Even [providing] fluoride toothpaste for individuals would be 10 to 20 times more costly than water fluoridation. Using fluoride mouth rinses or going to the dentist to get fluoride treatments would be much more expensive."
Levy would like to see more high-quality research on the topic before long-standing policies get upended. But even without more scientific clarity, the debate is likely to escalate. The Environmental Protection Agency is facing a late-January deadline, should it appeal the federal court decision ordering it to reduce fluoride risks.
And Robert F. Kennedy Jr. will soon face confirmation hearings where he may have to answer direct questions about views he has aired on fluoride in the past.
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