A large U.S. study has found that children whose mothers lived in areas with higher levels of fluoride in public drinking water during pregnancy tended to score lower on tests of fluid cognition, particularly when fluoride concentrations approached or exceeded the level recommended for community water fluoridation. The research, supported by the National Institutes of Health’s Environmental influences on Child Health Outcomes Program, examined 2,514 children born between 2006 and 2019 and followed them until cognitive testing between the ages of 3 and 17. The findings do not establish that fluoride caused differences in children’s cognitive performance, but they add to an increasingly consequential debate about how prenatal exposure to environmental chemicals may influence early brain development.
Fluoride is a naturally occurring mineral found in soil and water, and it is deliberately added to many public water systems because it strengthens tooth enamel and helps reduce dental decay. In the United States, the U.S. Public Health Service recommends a fluoride concentration of 0.7 milligrams per liter, or 700 micrograms per liter, in fluoridated drinking water. The Environmental Protection Agency’s enforceable maximum contaminant level is considerably higher, at 4 milligrams per liter. Much of the scientific concern surrounding fluoride and neurodevelopment has historically focused on substantially higher concentrations, including levels above 1,500 micrograms per liter. The new analysis addresses a more difficult question: whether differences in fluoride exposure within the range encountered by many U.S. communities may also be associated with childhood cognition.
Researchers led by Katrina Simon, PhD, of Columbia University Mailman School of Public Health, linked fluoride measurements from public water systems with residential address information collected from participants during pregnancy. This approach allowed the investigators to estimate the concentration of fluoride in the water available to pregnant mothers, rather than relying only on a single self-reported exposure measurement. The analysis was limited to public drinking water and therefore did not capture the full amount of fluoride each mother may have encountered. Toothpaste, tea, food, dietary supplements, bottled water, private wells, and other sources can all contribute to an individual’s total fluoride exposure, creating an important limitation when interpreting the results.
The children later completed standardized assessments from the NIH Toolbox Cognition Battery, a set of computerized and performance-based tests designed to measure several dimensions of thinking. The study concentrated on fluid cognition, which involves solving unfamiliar problems, retaining and manipulating information, maintaining attention, and adapting to new situations. These abilities are distinct from crystallized cognition, which reflects knowledge accumulated through learning and includes skills such as vocabulary. After accounting for parental education, parental age, prenatal tobacco exposure, child sex, season of conception, and neighborhood characteristics, the researchers observed an inverse association between estimated prenatal fluoride exposure and fluid cognition.
The relationship was not uniform across the entire fluoride range. The investigators reported that associations became apparent when public-water fluoride levels approached approximately 675 micrograms per liter, a concentration close to the U.S. recommended level of 700 micrograms per liter. Above that threshold, every 500-microgram-per-liter increase in fluoride was associated with an average decline of 3.36 points on the standardized fluid cognition scale. The estimate describes a statistical difference across groups rather than a predictable change in an individual child, and it does not mean that every child exposed to higher fluoride levels will experience impaired development. Nevertheless, the dose-related pattern is likely to attract attention because it appeared near a concentration used in routine water fluoridation.
The researchers also found that the apparent association was specific to fluid cognition. Across the ages studied, prenatal fluoride levels were not linked to crystallized cognition, suggesting that the exposure did not show the same relationship with learned knowledge and vocabulary. The differences were more pronounced among children younger than 7 years than among older children. This age pattern may indicate that early childhood assessments are more sensitive to subtle variations in specific cognitive processes, or it may reflect differences in how cognition develops and is measured at different ages. The authors emphasized that additional research is needed before the age-related finding can be interpreted biologically.
The study’s design provides a broad view of real-world exposure but also prevents researchers from making definitive causal claims. It was observational, meaning that participants were not randomly assigned to different fluoride concentrations. Families living in areas with different water characteristics may differ in ways that are difficult to measure completely, including diet, health care access, housing conditions, educational opportunities, and exposure to other environmental substances. Although the statistical models adjusted for several potential confounding factors, residual confounding remains possible. In addition, estimating exposure from public water records and residential addresses cannot determine how much water an individual mother consumed or how much fluoride entered her body.
The findings arrive as scientists and public health agencies continue to weigh the dental benefits of fluoridation against questions about possible developmental effects. The study did not assess whether community water fluoridation prevented cavities in the participating children, nor did it compare the overall health benefits and risks of fluoridation programs. It also did not measure fluoride concentrations in blood, urine, amniotic fluid, or fetal tissues, which would provide more direct information about biological exposure. Instead, it evaluated the relationship between environmental fluoride measurements during pregnancy and later cognitive test scores, an approach that is useful for population-level investigation but necessarily less precise for individual exposure assessment.
Anne Nigra, PhD, a co-senior author from Columbia University Mailman School of Public Health, said that the use of fluoride measurements collected through routine public-water monitoring may help inform future evaluations of drinking-water guidelines. Amy Margolis, PhD, of The Ohio State University Wexner Medical Center and College of Medicine, said that continued research into fluoride and other environmental exposures will be important for understanding the development of children’s thinking and learning processes. The authors say future studies should examine when the developing brain may be most sensitive to fluoride, measure exposure from all relevant sources, and evaluate developmental outcomes alongside dental health benefits.
Published in the American Journal of Epidemiology, the analysis adds a new data point to a long-running scientific discussion about prenatal environmental exposures and childhood development. Its most important message is not that fluoride has been proven to damage cognition, but that associations may warrant closer examination even at concentrations near current U.S. guidance. Larger prospective studies with direct biological measurements, detailed dietary information, repeated developmental assessments, and stronger control of co-exposures will be needed to determine whether the observed pattern reflects a causal effect or a combination of other factors. Until then, the researchers stress that their results should be understood as evidence of an association, not proof that fluoride caused the cognitive differences observed in the children.
Subject of Research: People
Article Title: Prenatal exposure to fluoride in public water and child cognition in the US ECHO Cohort, 2006–2019
News Publication Date: 14-Aug-2026
Web References: https://doi.org/10.1093/aje/kwag186; https://echochildren.org/; https://nihtoolbox.org/domain/cognition/
References: Simon KR, Bloomquist TR, Rajeev T, Hernandez A, Kulali S, Burjak M, Kress AM, Palmore M, Akbaryan A, Sanchez TR, Ornelas Van Horne Y, Shin HM, Goin DE, Tamayo-Ortiz M, Patel GH, Shuffrey LC, Ghassabian A, Karagas MR, Leventhal L, Fry RC, Miller RL, Herbstman J, Morales S, Margolis AE, Nigra AE. “Prenatal exposure to fluoride in public water and child cognition in the US ECHO Cohort, 2006–2019.” American Journal of Epidemiology. 2026. DOI: 10.1093/aje/kwag186.
Image Credits: Environmental influences on Child Health Outcomes (NIH ECHO Program)
Keywords: Water fluoridation, fluoride exposure, pregnancy, prenatal exposure, child cognition, cognitive development, fluid cognition, neurodevelopment, public drinking water, observational study, environmental health, NIH ECHO Program
