A large new study published April 13 in the Proceedings of the National Academy of Sciences found no association between community water fluoridation and reduced IQ or worse cognitive functioning at any life stage. Researchers report no measurable difference in cognitive outcomes between people who grew up with fluoridated municipal water and those who did not.
Study design and findings
The study was led by Rob Warren, PhD, of the University of Minnesota, using data from the Wisconsin Longitudinal Study, which has tracked more than 10,000 Wisconsin high school graduates from the class of 1957. Participants completed IQ testing at age 16 and underwent cognitive assessments at roughly ages 53, 64, 72, and 80. Because biological fluoride measures were not available, researchers estimated exposure by matching participants’ places of residence with records of when community water fluoridation began.
Across those life stages, the team found no evidence that growing up with community water fluoridation was associated with lower adolescent IQ or impaired adult cognitive functioning. The authors contrast their results with some earlier studies that reported links between fluoride and lower IQ, noting that many of those studies were conducted in settings with far higher fluoride concentrations than typical U.S. community fluoridation programs. Warren previously led a November 2025 analysis that reached similar conclusions for brain function at age 60.
How this fits with recent policy debate
The new findings come amid renewed scrutiny of fluoridation. The report differs from policy moves by HHS Secretary Robert F. Kennedy Jr., who directed the CDC to revisit its recommendation to add fluoride to drinking water. Experts responding to the study emphasized that, at the fluoride concentrations used for U.S. community fluoridation, there is no evidence of adverse neurodevelopmental or cognitive effects.
Expert reaction and context
Dental and pediatric experts called the results reassuring. A spokesperson for the American Dental Association framed the study as timely information that counters misinformation and reinforces that fluoridation at U.S. levels does not affect IQ or cognition. Pediatricians cited the findings as support for using fluoride in appropriate amounts while noting that very high fluoride exposures can be harmful, as is true for many common substances.
A brief history and current policy
Fluoride’s dental benefits were first noted in 1909, and Grand Rapids, Michigan, became the first U.S. city to add fluoride to municipal water in 1945. The U.S. Public Health Service recommended fluoridation in 1962. The CDC currently identifies an optimal fluoride concentration of 0.7 milligrams per liter (mg/L) to prevent cavities; the legal limit in U.S. drinking water is 4 mg/L. More than 70% of people served by U.S. public water systems—over 200 million Americans—receive fluoridated water, though some communities and states have moved to limit or ban it. Two states, Utah and Florida, have enacted bans, and some localities have discontinued fluoridation since the mid-1990s.
Benefits, mechanisms, and risks
Fluoride is a naturally occurring mineral found in water and dental products. It helps prevent tooth decay by inhibiting decay-causing bacteria, strengthening enamel, and helping reverse early lesions. Public health evidence shows fluoridation reduces tooth decay, decreases cavity severity, lowers dental treatment costs, and reduces missed school and work days. The most common adverse effect of excessive fluoride intake is dental fluorosis, which usually appears as white spots or, in more severe cases, brown staining on teeth. Extremely high fluoride exposures can cause other harms, but those levels are well above those used for community water fluoridation in the U.S.
Practical guidance
Public health agencies recommend maintaining good oral hygiene and limiting sugar intake alongside fluoridated water and fluoridated toothpaste. Recommended habits include brushing at least twice daily, flossing, and regular dental visits. Pediatricians also advise parents to model brushing, limit sugary drinks and sticky snacks, and avoid letting infants fall asleep with bottles containing sugary beverages. Experts note that while universal access to high-quality dental care and perfect habits could reduce the need for community fluoridation, current access gaps mean fluoridation remains a cost-effective measure for preventing cavities and protecting population oral health.