A new fluoride and IQ study has found no evidence that community water fluoridation harms children’s intelligence or adults’ cognitive function. The research, published in the Proceedings of the National Academy of Sciences on April 13, examined long-term data from Wisconsin and adds to a growing body of U.S. evidence showing no measurable link between fluoridated drinking water and lower IQ.
The findings arrive as fluoride in drinking water remains a national flashpoint. Utah and Florida have enacted bans on fluoride in public drinking water, and more cities and counties have moved to stop adding it, even as many health groups continue to support fluoridation as a tool to prevent tooth decay.
What the study found
The study was led by researchers at the University of Minnesota and drew on Wisconsin state testing records, archival information showing when cities began fluoridating their water, and the Wisconsin Longitudinal Study. That long-running project has followed a random sample of 10,317 high school seniors since their 1957 graduation, with follow-up continuing through 2026.
Researchers used those records to examine whether childhood exposure to community water fluoridation was linked to adolescent IQ or later-life cognitive performance. Across the analysis, they found no evidence supporting a connection between fluoridated drinking water and children’s IQ. They also found no evidence that fluoridation was tied to cognitive functioning later in life.
The study tracked people far beyond childhood. Participants took IQ tests at age 16, and later completed cognitive testing at ages 53, 64, 72, and 80. According to the reporting on the study, people exposed to fluoride in drinking water did not score differently from people who were not exposed when researchers looked at intelligence and cognitive function across those stages of life.
How exposure was measured
The research did not rely on direct biological measurements such as urine or blood samples. Instead, the team estimated fluoride exposure based on where participants lived and when community water fluoridation began in those areas.
That approach gave the researchers a way to study a large population over many decades, but it also came with limits. The study’s authors and outside coverage noted that exact fluoride levels for each person could not be measured because the original Wisconsin study was not designed to track fluoride exposure directly.
Even with those limits, the study is notable for its size and long follow-up period. Reports on the findings describe it as the first U.S. study to follow childhood exposure to community water fluoridation into older adulthood while examining cognitive outcomes over the life course.
Debate over fluoride evidence
The new results differ from the National Toxicology Program’s monograph on fluoride exposure and cognition. The NTP concluded, with moderate confidence, that higher levels of fluoride exposure, such as drinking water containing more than 1.5 milligrams of fluoride per liter, are associated with lower IQ in children.
But the NTP also said its review was designed to evaluate total fluoride exposure from all sources, not the health effects of fluoridated drinking water alone. Coverage of the new Wisconsin analysis also noted that earlier studies raising concerns often involved much higher fluoride concentrations than those typically used in U.S. community water systems.
That distinction has become central to the public debate. Supporters of fluoridation argue that studies involving higher exposures do not answer the policy question facing U.S. communities, where the recommended level for cavity prevention is 0.7 milligrams per liter. Reporting on the new study said the Wisconsin analysis found no association between community water fluoridation at that guideline level and cognitive outcomes across life.
Why the issue matters
Fluoride is a naturally occurring mineral that strengthens teeth and helps reduce cavities. It is added to some drinking water systems as a public health measure, and health organizations including the American Dental Association and the American Academy of Pediatrics support fluoridation at recommended levels.
The ADA said recent U.S.-based analyses show fluoride at recommended levels does not affect cognition in adolescence or later adult life. The group also said community water fluoridation typically reduces tooth decay by about 25% and that ending fluoridation has consistently been linked to higher cavity levels and greater restorative needs.
For now, the new study is likely to add fuel to an already heated policy fight. It does not end the broader dispute over fluoride, but it does offer fresh U.S. evidence that community water fluoridation, at levels commonly used in public drinking water, was not linked to lower IQ or worse brain function in the Wisconsin population studied.
