Pregnant women exposed to public drinking water fluoride levels near or above 675 µg/L appeared to have children who scored lower on cognition tests as levels rose. The study was published in the American Journal of Epidemiology.
To properly protect neurodevelopment, current U.S. Environmental Protection Agency (EPA) maximum contaminant levels in community water systems may need to be reevaluated, the authors wrote.
“Prenatal fluoride exposure in regulated public water is nonlinearly associated with lower fluid cognition scores in U.S. children at concentrations below current WHO and U.S. EPA thresholds,” wrote the authors, led by Katrina Simon, PhD, of the Columbia University Mailman School of Public Health (Am J Epidemio, August 14, 2026).
For decades, the U.S. Centers for Disease Control and Prevention supported community water fluoridation as a safe and cost-effective strategy for preventing tooth decay and reducing cavity rates. However, the issue has gained renewed attention after Kennedy criticized fluoride and expressed support for reversing recommendations supporting the practice.
Furthermore, a recent review from the U.S. National Toxicology Program explored evidence linking fluoride exposure levels above 1,500 ųg/L in drinking water with lower IQ scores in children. However, most community water systems in the U.S. have lower fluoride levels. Nevertheless, questions remain about links between lower levels typically found in the U.S. and lower IQ scores in children.
To explore correlations, researchers used observational data from the Environmental influences on Child Health Outcomes (ECHO) cohort, which includes 2,514 children born between 2006 and 2019 across 17 sites in 23 states. By linking census tract-level concentrations to residential addresses across pregnancy, individual prenatal time-weighted average public water fluoride concentrations were estimated. U.S. National Institutes of Health Toolbox scores were used to assess fluid and crystallized cognition, which includes learned knowledge like vocabulary, according to the study.
Children whose mothers had higher estimated fluoride levels in public drinking water during pregnancy appeared to score lower on tests of fluid cognition, including problem-solving, memory, attention, and the ability to adapt to new information, the authors wrote.
Moreover, greater fluoride levels appeared to be only associated with lower fluid cognition scores when water fluoride levels were near 675 ųg/L or higher. The current U.S. Public Health Service recommended level is 700 ųg, or 0.7 mg/L for fluoridated water, and the EPA’s current regulatory level is 4,000 ųg/L.
Levels above 675 ųg/L -- each 500 ųg/L increase in fluoride -- were linked to an average 3.36-point lower score on the standardized fluid cognition scale, they wrote.
Notably, the researchers did not appear to find a correlation between fluoride and crystallized cognition, the authors wrote.
Since this was an observational study, researchers emphasized that the results show a link between prenatal fluoride exposure and children’s cognition; they do not prove that fluoride caused differences in cognitive performance, they wrote.
Nevertheless, the study had limitations, including the measurement error in exposure. The research did not measure total fluoride exposure, the authors wrote.
“In this pooled cohort study of children across the U.S., we observed nonlinear, inverse associations between prenatal public water fluoride and child fluid cognition at concentrations below the current WHO guideline (1,500 ųg/L) and near the current USPHS optimal fluoridation guideline (700 ųg/L),” Simon and team wrote.
