Fluoride in Drinking Water Not Linked to Cognitive Decline: Study
USA: A long-term study published in Proceedings of the National Academy of Sciences has found that fluoride exposure through drinking water had no significant impact on IQ or brain function, supporting its neurological safety.
The findings are from an extensive analysis led by John Robert Warren and colleagues, who examined the relationship between community water fluoridation (CWF) and cognitive outcomes from adolescence into later life. The research draws on data from the Wisconsin Longitudinal Study, a large and representative cohort that has tracked individuals over several decades, offering a rare opportunity to assess long-term cognitive effects.
Community water fluoridation has long been implemented as a public health measure to reduce dental caries, but concerns about its potential neurological effects have gained attention in recent years. Some earlier reports, including those cited in policy decisions to discontinue fluoridation in certain regions of the United States, suggested a possible link between fluoride exposure and lower IQ. However, many of those studies were based on unusually high fluoride levels or lacked representative population samples.
To address these limitations, the present study utilized historical records to determine fluoride exposure at the community level, alongside standardized measures of adolescent IQ and cognitive performance later in life. Adolescent IQ was assessed using school-based testing, while adult cognition was evaluated at multiple stages, including midlife and older age, using established neurocognitive tools.
Key Findings:
- The analysis included data from over 10,000 individuals from the Wisconsin high school graduating class of 1957.
- Key socioeconomic and demographic factors influencing fluoride exposure and cognitive outcomes were accounted for in the analysis.
- Residential stability was assessed to better estimate consistent exposure to fluoridated water during childhood.
- After adjustments, no significant differences in cognitive performance were observed between individuals exposed to fluoridated water and those who were not.
- The findings were consistent across all life stages evaluated, from adolescence to older adulthood.
- Only a very small number of statistical comparisons showed any differences.
- The observed differences were consistent with what would be expected by chance alone.
The study further strengthens earlier research by directly evaluating IQ rather than relying solely on academic performance, and by improving the accuracy of exposure assessment through tracking residential history. These methodological enhancements provide greater confidence in the findings.
While the authors acknowledged certain limitations—such as the inability to directly measure individual fluoride intake—the overall evidence did not support any association between recommended levels of community water fluoridation and adverse cognitive effects.
In summary, the large, population-based study adds to the growing body of evidence indicating that fluoridated drinking water, at levels used in public health programs, does not impair cognitive development or function. The findings may help inform ongoing public health discussions and policy decisions regarding the safety and benefits of water fluoridation.
Reference:
Warren, J. R., Rumore, G., Sicinski, K., Herd, P., & Engelman, M. (2026). Municipal water fluoridation, adolescent IQ, and cognition across the life course: Evidence from the Wisconsin Longitudinal Study. Proceedings of the National Academy of Sciences, 123(16), e2536005123. https://doi.org/10.1073/pnas.2536005123
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