A landmark U.S. study published on April 13, 2025 in the Proceedings of the National Academy of Sciences found no connection between fluoride in drinking water and IQ scores or cognitive ability at any point from childhood through age 80. The research, led by Dr. John Robert Warren, a sociologist and population health expert at the University of Minnesota, is the first of its kind to examine the fluoride and IQ study question using population-representative American data, tracking real people across seven decades of life. The findings are directly relevant to parents anxious about fluoride drinking water safety – and come at a moment when public debate over the topic has grown unusually loud.
If you have been following the news around fluoride, you already know that the conversation has gotten complicated. Water fluoridation – the controlled addition of fluoride to public water supplies at low concentrations to prevent tooth decay – has been a standard public health practice in the United States for over 80 years. Health organizations including the American Academy of Pediatrics, the American Dental Association, and the Centers for Disease Control and Prevention all agree that water fluoridation is effective, safe, and works to prevent tooth decay. But in recent years, claims that fluoride harms the developing brain have gained traction online and in political circles, prompting families to second-guess a practice that has been part of American infrastructure for generations.
The PNAS fluoride study does not settle every open question – researchers are transparent about that. But it delivers something genuinely useful: the most rigorous long-term look at fluoride cognitive effects in an American population ever conducted. Here is what it found, what it does not claim to prove, and what it means for your family’s tap water.
What the PNAS Fluoride Study Actually Did
Dr. Warren began the project because high-quality U.S. data on the question simply did not exist. His is the first robust American-based study of water fluoridation’s possible effects on intelligence and brain function from the teen years into older adulthood. Previous research that raised concerns had been conducted in other countries, often in areas where naturally occurring fluoride levels in the water were dramatically higher than anything found in U.S. municipal systems.
The study examined Wisconsin state testing records, archival information about when Wisconsin cities began to fluoridate their water, and data from the Wisconsin Longitudinal Study, which has followed a random sample of 10,317 high school seniors from 1957 through 2026. That is not a small sample chased for a few years – it is more than 10,000 people tracked across their entire adult lives. Participants took IQ tests at age 16, then completed cognitive testing later in life at ages 53, 64, 72, and 80. That level of follow-through is rare in public health research, and it’s what makes this dataset so valuable.
To estimate each person’s fluoride exposure, researchers used records of when community water fluoridation began in certain areas, and the locations of untreated wells. Across multiple statistical models and sensitivity analyses, community water fluoridation at the current guideline level of 0.7 milligrams per liter was not associated with cognitive outcomes across the course of a life. Zero association – not at age 16, not at 53, not at 80.
What the Study Found – and What It Confirmed
The headline result is straightforward. There is no evidence supporting a connection between community water fluoridation and children’s IQ. There is also no evidence supporting a connection between community water fluoridation and cognitive functioning at various points later in life.
A press release from the research team explained that participants exposed to community water fluoridation as adolescents “did not perform significantly worse or better than peers who were never exposed to fluoridated water as adolescents – at any of the ages at which IQ or cognition was assessed.” That consistency across age groups matters. If fluoride were quietly suppressing brain development in childhood, you would expect some ripple effect to show up in later-life cognition. It did not.
This also builds on prior work. The new research extends an earlier Warren study published in December 2025, which found no link between community water fluoridation in early life and tests of brain function at age 60. Together, the two studies create the most complete picture yet of fluoride’s relationship – or lack of one – with the human brain over a lifetime. The findings also confirm evidence published in previous research which used a national sample but considered school achievement test scores instead of actual IQ scores.
Warren himself put it plainly. “There’s now good reason to doubt the claim that fluoride causes reduction in IQ,” he said.
Does Fluoride in Drinking Water Lower IQ? What Experts Say
The study drew praise from researchers who work in this area and had no stake in the outcome. Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada, called Warren’s latest research “one of the more rigorous attempts to examine fluoridation and cognition across the life course.” That endorsement carries particular weight because Lanphear is not a fluoride advocate – he published a 2019 study that found slightly lower IQ scores in young children whose mothers had higher levels of fluoride in their urine during pregnancy.
Dr. Scott Tomar, head of the department of population oral health at the University of Illinois in Chicago, called the new study “quite significant,” adding: “There is no association with community water fluoridation and any measure of IQ or neurodevelopment.” Tomar was not involved in the research.
Steven Levy, a dentist and public health researcher at the University of Iowa who was also not involved in the study, described the data as “very strong,” saying: “There’s no strong signal at all coming through that should give us concern.”
The consistent message from independent experts: at the amounts added to U.S. drinking water, fluoride cognitive effects on IQ simply do not show up in the data. Lead researcher Warren noted that communities have been removing fluoride “based on flawed studies that considered the IQ effects of exposure to massive doses of fluoride,” adding that because U.S. fluoridation levels are so much lower, “almost all prior evidence from those international studies is not relevant to U.S. public policy debates.”
Why Earlier Studies Raised Concerns
It would be unfair to dismiss the earlier alarm completely without explaining where it came from. Many scientists were less than fully convinced by the earlier claims, pointing out that much of the underlying evidence drew from populations exposed to substantially higher fluoride concentrations than those commonly found in North American drinking water, and that none of the studies were conducted in the United States.
A 2025 meta-analysis published in JAMA Pediatrics by researchers at the National Institute of Environmental Health Sciences reviewed 74 previous epidemiological studies and did find an association between higher fluoride exposure and lower IQ in children. But the key word is “higher.” That meta-analysis found that for every 1 mg/L increase in urinary fluoride, there was a decrease of 1.63 IQ points in children. However, the U.S. Public Health Service’s recommended fluoride concentration is 0.7 mg/L – and there were not enough data in that review to determine whether 0.7 mg/L affected children’s IQ at all.
The optimal level of fluoride in U.S. drinking water to prevent cavities is 0.7 milligrams per liter, according to the CDC – roughly the equivalent of 3 drops in a 55-gallon barrel. The studies that found harm were largely looking at populations drinking water with fluoride at two, three, or even four times that level – in some cases from naturally occurring deposits, not deliberate addition. Comparing those settings to American tap water is like comparing a sunburn to a warm afternoon outside.
Is Fluoridated Water Safe for Children’s Brain Development?
This is the question most parents are actually asking, and the answer from this research is yes – with the honest caveat that no study covers every possible scenario.
Fluoride in drinking water at the recommended level has not been linked to lower IQ scores. Some studies, including from the U.S. government, have noted a possible link between very high fluoride levels – more than twice the level used in U.S. drinking water – and lower IQ scores in children. Those findings were based on studies in non-U.S. countries where some pregnant women and children were exposed to total amounts higher than 1.5 mg of fluoride per liter of drinking water.
Warren’s study adds the critical piece that had been missing: American data, tracked across American lifetimes, at American fluoridation levels. Warren acknowledges that his study includes mostly white participants because it draws from Wisconsin high school graduates, and says he would like to see more research on the topic, including a study that could follow participants from birth. That transparency is a sign of good science, not a red flag.
Parents who drink bottled water exclusively or who live in areas without fluoridated supply should also know that there are practical steps available. The American Academy of Pediatrics continues to recommend age-appropriate amounts of fluoride toothpaste and fluoridated water to protect children’s teeth, and if you live in an area without fluoridation, it is worth talking to your pediatrician about fluoride supplementation.
The Political Context Around This Research
It would be impossible to discuss this study without acknowledging why it was needed in the first place. The results contradict claims made by Health Secretary Robert F. Kennedy Jr. that fluoride is “industrial waste” associated with IQ loss. Those claims contributed to real policy changes: since 1995, 86 Wisconsin communities have stopped adding fluoride to municipal water systems, according to the state’s Department of Natural Resources. Similar removals have occurred in Utah, Florida, and elsewhere.
Warren set out to evaluate whether the IQ claim was actually backed by U.S. data, after hearing Kennedy tout the research while arguing that fluoride exposure could harm children’s brains. What he found was that it was not. More recently, the Trump administration appears to have softened its position on fluoride. In March, CDC director Dr. Jay Bhattacharya told a House Appropriations subcommittee that “fluoride is essential for oral health,” though he maintained that excessive amounts “can have neurological and developmental impacts.”
That middle-ground position – fluoride at recommended levels is fine; very high doses are a separate concern – is actually consistent with where the evidence sits. The two ideas are not in conflict. What the PNAS study challenges is the blanket claim that the fluoride added to American tap water in any amount is harming children’s brains. On that specific question, the data say no.
Has Fluoride Been Proven to Cause Cognitive Decline?
No – and that framing is worth unpacking. “Proven” is a high bar in any scientific field, and the honest answer is that the body of evidence, taken as a whole, does not support a conclusion that community water fluoridation at U.S.-recommended levels causes cognitive decline. Study co-author Gina Rumore, co-director of the Demography and Economics of Aging Coordinating Center at the University of Minnesota, stated that the findings “provide no support for the claim that community water fluoridation has any harmful effect on children’s IQ or on adult cognition.”
That said, a few limitations in the PNAS research are worth knowing about if you want the full picture. Christine Till, a neuropsychologist at York University in Toronto, noted that because the participants were born before widespread water fluoridation, the analysis does not capture exposure during particularly sensitive early life periods such as gestation and infancy, when the brain is developing most rapidly. Dr. Lanphear also pointed out that the study did not measure how much fluoride individuals actually consumed – it infers exposure from place of residence – and cannot account for total intake from sources such as infant formula, toothpaste, or diet.
These are not disqualifying flaws; they are the normal limits of working with longitudinal population data. The researchers are upfront about them, which is exactly what you want to see. Warren himself said his studies should not be interpreted as the final word on the matter, and that they should prompt additional research. Science rarely delivers one single conclusive study – it builds a picture gradually, and this study adds a large, detailed, well-constructed piece.
What to Keep in Mind for Your Family
Parents making decisions about fluoride exposure right now can draw a few clear, evidence-based takeaways from this research.
First, the fluoride added to American tap water – at the CDC’s recommended level of 0.7 mg/L – has not been shown to reduce IQ or harm cognitive development in children or adults across their lifespan. That is the direct conclusion of the most rigorous US study on fluoride child development and cognition ever published. It covers everyone from teenagers to 80-year-olds, and it finds nothing to worry about at normal exposure levels.
Second, the concerns that have circulated online largely stem from studies conducted in countries where fluoride levels in water were far higher than U.S. standards – often from natural sources rather than deliberate addition. Those findings are not a direct comparison to what is in American taps. Warren notes that it is well established that community water fluoridation reduces cavities by about 25%, according to the CDC. America has been preventing tooth decay with fluoridated water for over 80 years. That is a long track record.
If you have specific concerns about your local water supply – fluoride levels can vary by region and even by source – contact your local water provider directly. The CDC also offers a search tool to look up fluoride content in local water systems, though it is not fully complete for every area. If your water comes from a private well, have it tested at a certified lab. And if you have questions about fluoride toothpaste amounts for young children, your child’s pediatric dentist is the best person to ask – recommendations differ by age, and getting that right matters for dental health without any cognitive trade-off whatsoever.
What This Means for You
The PNAS water fluoridation research gives parents something genuinely useful: a clear, long-running American study that found no link between community fluoridated water and IQ loss at any stage of life. The fluoride and IQ study question has been argued loudly for years, often with more heat than light. This research adds the most rigorous evidence yet that, at U.S. drinking water levels, fluoride brain health concerns tied to IQ simply are not supported by American data.
That does not mean every question is closed – researchers themselves are calling for more studies, particularly ones that track fluoride exposure from birth and across more diverse populations. But for the vast majority of American families drinking tap water at standard fluoridation levels, the current body of evidence – now anchored by this landmark study – is reassuring. Your tap water is not the threat to your child’s intelligence that some headlines have suggested. The biggest thing you can do for your child’s long-term health remains the unglamorous basics: regular dental checkups, age-appropriate fluoride toothpaste in the right amounts, and a pediatrician you trust enough to call when something does not add up.
Disclaimer: This article was created with AI assistance and edited by a human for accuracy and clarity.