Fluoridated water linked to better adolescent school achievement

Fluoride and fear 

By Justin Jackson, Medical Xpress

edited by Sadie Harley, reviewed by Robert Egan

Don't need no stinking fluoride!

Children exposed to recommended levels of fluoride in drinking water show modest cognitive advantages in secondary school, with no clear evidence of harm to cognitive functioning around age 60, according to researchers at the Institute for Social Research and Data Innovation at the University of Minnesota and multiple collaborating institutions.

Water fluoridation in the United States began after decades of research linked naturally high levels of fluoride in water sources to lower community tooth decay. The evidence was convincing enough for the city of Grand Rapids, Michigan, to become the first in the world to supplement its municipal water with fluoride in 1945.

While scientific consensus and public policy have considered fluoridation a fundamentally positive public health intervention, discussion, doubt, and conspiratorial fears have persisted in some public circles.

Some of the concerns revolve around safety for developing children, specifically regarding whether fluoride exposure reduces childhood IQ, with some selective scientific backing.

A previous meta-analysis that reported statistically significant inverse relationships between fluoride exposure and childhood IQ involved very poor rural populations in countries such as China, India, Mexico, and Iran and did not include US children or nationally representative samples. Findings at concentrations below 1.5 mg/liter were described as null, and concentrations above 1.5 mg/L were noted to exceed typical US exposures (around 0.7 mg/L).

A second meta-analysis was limited to studies in areas with fluoride concentrations equal to or below 1.5 mg/liter and reported no association between exposure to water fluoridation and lower IQ scores in children. Studies in that review also did not involve US children or nationally representative samples.

National cohort and typical US exposures

In the study, "Childhood fluoride exposure and cognition across the life course," published in Science Advances, researchers used nationally representative longitudinal data to investigate how fluoride exposure from drinking water during childhood relates to cognition in adolescence and around age 60.

Investigators used the High School and Beyond 1980 cohort, a sample of sophomores and seniors attending 1,020 US high schools in 1980. A subset of 26,820 individuals was followed through 2021. Analyses of adolescent cognition included 57,960 students, and analyses of cognition at about age 60 included 13,260 participants.

Adolescent cognition was measured using 12th grade reading comprehension, vocabulary, and mathematics scores. Cognitive functioning around age 60 was measured using a global score derived from a hierarchical item response theory model combining information from memory, fluency, and attention measures.

Linking subject to water sources

Researchers linked high school geolocations to Fluoridation Census records from 1967 through 1993, which reported whether and when localities supplemented municipal water with fluoride. Additional information came from US Geological Survey measurements of naturally occurring fluoride in 38,105 wells sampled between 1988 and 2017.

Exposure classification followed US Public Health Service recommendations indicating levels between 0.7 and 1.2 mg/liter until 2015 and 0.7 mg/liter beginning in 2015.

Sample members were placed into three exposure groups. One group lived in areas without municipal fluoridation and with naturally occurring fluoride below 0.7 mg/liter at conception and at the time of secondary school testing.

A second group lived in areas with municipal fluoridation or naturally occurring fluoride at or above 0.7 mg/liter at both time points. A third group lived in areas that implemented municipal fluoridation after conception but before secondary school tests.

Small gains in adolescent cognition

Students who grew up with recommended fluoride levels in their drinking water scored higher on secondary school tests of mathematics, reading, and vocabulary than peers who never reached those levels. Researchers describe these advantages as modest, about 7% of a standard deviation, and report that the pattern is consistently positive and statistically distinguishable from zero across all measures.

Analyses of global cognition around age 60 did not show statistically significant links with fluoride exposure.

Testing alternative explanations

In a robustness check focused on students who had not changed schools because of residential moves since the start of fifth grade. Results for that group closely matched the patterns found in the full analytic sample.

A second robustness check introduced an exposure category for communities that began municipal water fluoridation shortly after adolescent achievement tests were administered.

Analyses indicate that having stable community traits linked to fluoridation adoption (such as local politics, resources, social conditions, or investments in schools and health systems) is unlikely to be the reason children in fluoridated areas scored higher, which supports the interpretation that the association is connected to ingestion of fluoride, not types of communities.

Interpreting benefits and limits

Findings cast doubt on any assertions that exposure to recommended fluoride levels reduces academic achievement or cognitive functioning as the results pointed, albeit less dramatically, in the opposite direction. Fluoride exposure at levels routinely observed in the United States is associated with cognitive benefits in adolescence and is not harmful to cognitive functioning around age 60.

Study authors note that they were unable to infer from observational data and available measures why fluoride exposure relates to better adolescent academic achievement, only that it does.

Written for you by our author Justin Jackson, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

More information: John Robert Warren et al, Childhood fluoride exposure and cognition across the life course, Science Advances (2025). DOI: 10.1126/sciadv.adz0757

David A. Savitz, Evidence-based water fluoridation policy, Science Advances (2025). DOI: 10.1126/sciadv.aed4503

Journal information: Science Advances