Could childhood exposure to fluoridated water leave a lasting mark on cognition? Decades of data offer clues.
Fluoride in community drinking water is not linked to lower adolescent IQ or poorer thinking skills later in life, a long-running US study finds.
Researchers followed a generation of Wisconsin school-leavers, examining cognitive performance from adolescence into their eighties.
Those exposed to fluoridated water did not show a consistent disadvantage compared with people whose communities had no fluoridation.
The findings address concerns that adding fluoride to drinking water to prevent tooth decay could undermine intellectual development.
Professor John Robert Warren, the study’s first author, said:
“Utah, Florida and many municipalities have chosen to remove fluoride from drinking water based on flawed studies that considered the IQ effects of exposure to massive doses of fluoride.
Because levels of fluoride added to municipal drinking water in the U.S. are so much lower, almost all prior evidence from those international studies is not relevant to U.S. public policy debates.”
Tracking thinking over decades
The research draws on the Wisconsin Longitudinal Study, which began with over 10,000 people who graduated from high school in 1957.
Researchers combined school IQ records with historical information about community water fluoridation and naturally occurring fluoride levels.
Following participants into old age allowed researchers to examine whether childhood exposure was associated with lasting differences in cognitive performance.
Comparing communities requires care because their residents can differ in ways that also relate to cognitive performance.
Once those background differences were taken into account, there was no consistent evidence that exposure was associated with either better or worse performance.
The same broad pattern appeared when researchers focused on people who had lived in the same county since early childhood, increasing confidence in their estimates of exposure.
Overall, the findings suggest that growing up with fluoridated community water is not associated with poorer cognitive performance in old age.
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The study was published in the journal Proceedings of the National Academy of Sciences (Warren et al., 2026).
