Associations appeared when fluoride levels in neighborhood drinking water were close to or above current U.S. recommended levels.

Pregnant mothers who lived in neighborhoods where public drinking water fluoride levels were near or above the current U.S. recommended levels, tended to have children who scored lower on tests of fluid reasoning as fluoride levels increased, according to a new study supported by the National Institutes of Health’s Environmental influences on Child Health Outcomes (ECHO) Program.

Fluoride occurs naturally in some water sources and is commonly added to public water systems to help prevent cavities. The paper’s authors note that a recent National Toxicology Program review examined evidence linking fluoride exposure levels above 1,500 micrograms per liter in drinking water with lower IQ scores in children. However, most U.S. public water systems have lower fluoride levels, and questions remain about associations at lower levels typically found in the United States.

ECHO researchers looked at whether fluoride levels in public drinking water during pregnancy were related to cognitive scores assessed during childhood.

"This study addresses an important gap by evaluating prenatal water fluoride and child cognition in a large U.S. sample," said lead author Katrina Simon, PhD, of Columbia University Mailman School of Public Health. "Findings from this work offer evidence that can inform ongoing guidance aimed at supporting children's development."

Researchers reported that children whose mothers had higher estimated fluoride levels in public drinking water during pregnancy tended to score lower on tests of fluid cognition that include problem-solving, memory, attention, and the ability to adapt to new information. Higher water fluoride levels were only linked to lower fluid cognition scores when water fluoride levels were near and above 675 micrograms per liter, which is close to the current U.S. Public Health Service recommended level of 700 micrograms, or 0.7 milligrams, per liter for fluoridated water. The current regulatory level set by EPA is higher at 4,000 micrograms per liter. Above 675 micrograms per liter, each 500 micrograms per liter increase in fluoride was associated with an average 3.36-point lower score on the standardized fluid cognition scale.

Researchers also found that the relationship between prenatal fluoride levels and cognition was specific to fluid cognition. Importantly, the study did not identify a link between fluoride and crystallized cognition, which includes learned knowledge such as vocabulary, across all ages.

In addition, the associations appeared stronger when cognition was assessed at a younger age. Children younger than 7 years of age showed larger differences in cognition scores associated with higher prenatal fluoride exposure compared to older children. Additional research is needed to better understand these age-related findings.

The study included 2,514 children born between 2006 and 2019 who completed cognitive testing between ages 3 and 17.

To estimate prenatal water fluoride exposure, researchers linked publicly available drinking water fluoride measurements to residential address information collected during pregnancy from ECHO participants. The study focused specifically on fluoride levels in public drinking water systems and did not measure total fluoride exposure from all possible sources, such as toothpaste, tea, foods, supplements, bottled water, or private wells.

Researchers then compared these estimates with children's performance on NIH Toolbox cognition assessments, while accounting for factors such as parental education, parental age, prenatal tobacco exposure, child sex, season of conception, and neighborhood characteristics.

“Because our study used fluoride measurements from public water systems that are collected as part of routine drinking water monitoring, the findings may help inform future evaluations of public drinking water guidelines,” said co-senior author Anne Nigra, PhD, also of Columbia University Mailman School of Public Health.

Community water fluoridation has long been used as a public health measure intended to reduce tooth decay. The current study does not evaluate the overall benefits and risks of community water fluoridation

“This study adds to a large body of work that looks at how early exposure to environmental contaminants may be associated with the development of the thinking and learning processes that are important for children’s developmental outcomes,” said co-senior author Amy Margolis, PhD, of The Ohio State University Wexner Medical Center and College of Medicine. “Continuing to study fluoride and other exposures will be integral in best supporting children’s environmental health and well-being.”

The researchers emphasize that this was an observational study. The findings demonstrate an association between prenatal fluoride exposure and children's cognition, but they do not prove that fluoride caused differences in cognitive performance.

The authors noted that future research could focus on when children may be most sensitive to fluoride exposure and examine both potential developmental risks and dental health benefits to better understand relationships between fluoride exposure and child health.

This collaborative research was published in the American Journal of Epidemiology.

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. 2026. American Journal of Epidemiology. https://doi.org/10.1093/aje/kwag186

About ECHO
The ECHO Cohort Consortium is a research program supported by the National Institutes of Health (NIH) with the mission to enhance the health of children for generations to come. ECHO Cohort investigators study the effects of a broad range of early environmental influences on child health and development. For more information, visit echochildren.org.