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A long-term U.S. study has found that drinking fluoridated water during childhood does not affect intelligence or brain function later in life. The research, published Monday (April 13) in the Proceedings of the National Academy of Sciences, tracked thousands of Americans for decades and offers new evidence to address ongoing debates about the safety of adding fluoride to public water supplies.
The study is the first in the U.S. to compare cognitive outcomes, such as IQ scores and memory, in people exposed to fluoridated water versus those who were not, from teenage years up to age 80. The research used data from the Wisconsin Longitudinal Study, which has followed over 10,000 people since they graduated high school in 1957. Participants took IQ and cognitive tests at several points in their lives. The study found no measurable difference in intelligence or cognitive skills at any age between those who grew up drinking fluoridated water and those who did not.
The findings challenge claims made by some public figures, including Health Secretary Robert F. Kennedy Jr., who has argued that fluoride is harmful to brain development. Researchers and independent health experts say these new results provide strong reassurance that community water fluoridation, at levels recommended in the United States, is not linked to lower IQ or impaired brain function. Dr. Scott Tomar from the University of Illinois in Chicago, who was not involved in the study, said, "There is no association with community water fluoridation and any measure of IQ or neurodevelopment."
This new evidence comes as an increasing number of U.S. communities have chosen to stop adding fluoride to their water, citing concerns about possible effects on children’s IQ. Utah and Florida have enacted statewide bans, and similar legislation is pending in other states. However, experts point out that earlier studies suggesting a link between fluoride and lower IQ were mostly conducted in countries with much higher natural fluoride concentrations than are allowed in the U.S. For example, the U.S. Centers for Disease Control and Prevention (CDC) recommends an optimal fluoride level of 0.7 milligrams per liter for preventing cavities, while the legal limit is 4.0 mg/L.
A recent meta-analysis published in JAMA Pediatrics reviewed 74 studies from multiple countries. It found that higher fluoride exposure was associated with lower IQ scores in children, but most of those studies took place in areas with much higher fluoride levels than in typical U.S. water supplies. When the analysis considered studies with fluoride levels similar to U.S. standards (less than 1.5 mg/L), the association between fluoride and IQ disappeared.
Another large-scale U.S. study highlighted by Scientific American found that children exposed to recommended levels of fluoride performed slightly better on academic tests in high school, and there were no differences in memory or attention in adulthood. Researchers suggest that improved dental health, a known benefit of fluoride, could keep students in school and help academic performance.
Major U.S. health organizations, including the American Dental Association, the American Academy of Pediatrics, and the CDC, continue to support community water fluoridation as a safe and effective way to reduce tooth decay.
The study authors emphasize that while their research provides strong evidence about fluoride and cognition in the U.S., ongoing monitoring and further studies are encouraged. Policy discussions about fluoridation are expected to continue as new research emerges and more communities evaluate their local water practices.