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Recent findings published in Science Advances provide new evidence regarding the long-term cognitive effects of consuming fluoridated water during childhood. The study suggests that growing up in communities with water fluoridation levels typical of the United States does not harm brain development and may be associated with slightly higher academic achievement in adolescence. These results offer a counterpoint to ongoing debates and legal challenges asserting that current fluoridation practices lower intelligence quotients in children.
For decades, the practice of adding fluoride to public drinking water has been a cornerstone of dental public health. The United States began this initiative in 1945 in Grand Rapids, Michigan, after scientists discovered that fluoride could significantly reduce the incidence of tooth decay.
The Centers for Disease Control and Prevention eventually recognized water fluoridation as one of the ten great public health interventions of the 20th century. Despite the consensus among dental professionals regarding the benefits for oral health, questions regarding the safety of fluoride ingestion have persisted for nearly eighty years.
Current skepticism focuses largely on potential neurodevelopmental risks. Critics of water fluoridation argue that exposure to fluoride during critical periods of brain development lowers IQ in children. They frequently cite meta-analyses that found inverse relationships between fluoride exposure and cognitive ability.
However, the researchers behind the new study note a significant disconnect in that existing literature. Many of the studies demonstrating harm examined populations in China, India, Iran, or Mexico, where people were often exposed to fluoride levels far exceeding the concentrations found in U.S. tap water. In some of those cases, the fluoride levels were high enough to cause physical toxicity, known as fluorosis.
To address this discrepancy, a multidisciplinary team of researchers sought to evaluate the effects of fluoride at levels actually relevant to American policy. The team included sociologists, demographers, and neurologists from the University of Minnesota, the University of Wisconsin-Madison, the University of Texas at Austin, and Columbia University. Their goal was to determine if the specific concentration recommended by the U.S. Department of Health and Human Services—0.7 milligrams per liter—poses a risk to cognitive health over a person’s lifespan.
The investigators utilized data from the “High School and Beyond” cohort, a large longitudinal project that began in 1980. The original sample consisted of a nationally representative group of 58,270 high school sophomores and seniors from 1,020 schools across the United States. A subset of approximately 26,820 participants was selected for long-term follow-up and has been interviewed on multiple occasions, most recently in 2021. This design allowed the authors to observe cognitive outcomes at two distinct points in the life course: late adolescence and midlife.
To estimate fluoride exposure, the researchers reconstructed the water quality history of the communities where the students attended school. They accessed government records from 1967 through 1993 to identify which municipalities fluoridated their water and when they began the practice. Additionally, they used data from the United States Geological Survey to account for naturally occurring fluoride in untreated well water.
The team categorized the participants based on their access to fluoridated water from the time of conception through their high school years. Students were considered “consistently exposed” if they lived in areas where the water contained at least 0.7 milligrams of fluoride per liter for their entire childhoods. Those living in areas with levels below this threshold were classified as having insufficient exposure. The researchers then analyzed the students’ 1980 test scores in mathematics, reading comprehension, and vocabulary.
For the midlife analysis, the study examined cognitive performance in participants who were approximately 60 years old in 2021. This assessment used a sophisticated model to combine scores from tests measuring memory, fluency, and attention. Throughout their statistical modeling, the authors adjusted for various factors that could skew the results, such as family socioeconomic status, race, gender, urbanicity, and the region of the country.
The analysis revealed that students who had consistent access to recommended levels of fluoride performed better on high school academic tests than those who did not. The difference was modest but statistically distinguishable from zero. The advantage amounted to approximately 7 percent of a standard deviation in the test scores. This finding held true even after accounting for the fact that fluoridated water is more common in urban areas and specific regions that might have different educational resources.
Regarding cognitive health in later life, the results showed no evidence of harm. The association between childhood fluoride exposure and cognitive functioning at age 60 was not statistically significant. The data points trended slightly positive, mirroring the adolescent results, but the link was too weak to be considered definitive. Essentially, the researchers found that early-life exposure to fluoridated water had no negative impact on cognitive abilities as the participants entered their senior years.
“We find very small (in magnitude), positive conditional associations between adolescent fluoride exposure and academic achievement in high school; those associations are statistically distinguishable from zero,” explained corresponding author John Robert Warren, a professor and director of the Institute for Social Research and Data Innovation at the University of Minnesota.
“Associations between adolescent fluoride exposure and cognition at age ~60 are not distinguishable from zero. But the claims being made by those opposed to community water fluoridation practices are that fluoride exposure lowers young people’s IQs. The fact that we find small (in magnitude) positive associations between fluoride exposure and adolescent academic achievement contradicts those claims.”
To ensure the validity of their findings, the authors conducted a “future treatment” test. This statistical technique helps determine if the observed benefits were caused by the fluoride itself or by unmeasured characteristics of the towns that choose to fluoridate. For example, a town that fluoridates its water might also invest more in schools or healthcare. The results of this check supported the idea that the fluoride exposure itself, rather than general community characteristics, was associated with the higher test scores.
“The empirical evidence used most heavily by those opposed to community water fluoridation — best exemplified by the 2025 National Toxicology report and Taylor et al’s JAMA Pediatrics article that came out of it — is seriously flawed in a number of ways,” Warren told PsyPost.
“Most importantly, it only provides evidence about the effects of MASSIVELY high doses of fluoride as compared to VERY HIGH doses, which is not at all relevant to public policy debates in places like the United States. Also: That evidence does not come from population representative samples, has never used US data, often does not account for selection into treatment, etc.”
In an editorial accompanying the study, David A. Savitz of the Brown University School of Public Health contextualizes these findings within the broader history of the fluoridation debate. He observes that while early opposition was often rooted in political ideology, modern arguments have shifted toward environmental health concerns. Savitz points out that many recent studies claiming to show risks rely on data from countries with vastly different fluoride delivery systems, such as fluoridated salt in Mexico, or examine exposure levels that are irrelevant to U.S. policy.
Savitz argues that the new study is particularly significant because it addresses the specific policy question facing American communities: the safety of adding fluoride to water at 0.7 milligrams per liter. He notes that while biological markers like urinary fluoride are useful in some contexts, they do not directly answer whether municipal water treatment is safe. By focusing on the water supply itself, this study provides evidence directly applicable to city councils and voters.
Savitz’s arguments were echoed by Matthew Hobbs, a researcher affiliated with the University of Canterbury. “These findings align with decades of high-quality international research showing that concerns about fluoride and cognition stem from studies of populations exposed to extremely high fluoride levels, not from community water fluoridation,” he told the Science Media Centre.
“From a public health perspective, this matters. Community water fluoridation remains one of the most equitable and cost-effective ways to prevent tooth decay, particularly for children and for communities with limited access to dental care. This new evidence reinforces that we can continue to deliver these benefits without compromising cognitive health at any stage of life.”
The new research distinguishes itself by using a large, nationally representative sample of Americans, directly addressing the cognitive effects of fluoride concentrations actually used in U.S. municipal systems rather than the toxic levels often examined in international research. Additionally, the research utilizes a robust longitudinal design that tracks participants over several decades, allowing for a rare assessment of how early-life exposure relates to cognitive health in both adolescence and midlife.
But there are still some limitations to consider. A primary challenge was the lack of complete residential history for every participant. The researchers had to assume that students lived in the same community from birth until high school. While migration rates for children are generally low, any moves between fluoridated and non-fluoridated areas would introduce error into the exposure estimates.
Additionally, the study relied on community-level water data rather than individual consumption. The researchers could not measure how much tap water each child actually drank or how much fluoride they ingested from other sources, such as toothpaste. This is a common constraint in large-scale historical studies where collecting biological samples from the past is impossible.
Looking ahead, the research team is working to replicate these findings using the Wisconsin Longitudinal Study. That upcoming project will address some of the current limitations by using actual IQ scores and linking participants to historical census records from 1940 and 1950. This will allow the researchers to verify residence at precise ages in early childhood, providing a more rigorous test of the fluoride-cognition link.
“Although the sample is only from Wisconsin (participants are a 1/3 random sample of 1957 Wisconsin high school seniors, followed prospectively since 1957), these new analyses improve on the ‘High School and Beyond’ analyses in two ways,” Warren explained. “(1) We have real IQ scores, not just academic achievement and (2) 90%+ of the records have been linked to the 1940 and 1950 US Censuses, when participants would have been ages 1 and 11, respectively. Thus we can restrict the analyses to people who lived in their same HS community in 1950 (age 11) and in 1940 (age 1).”
“The results are preliminary, but they exactly mirror those in the ‘High School and Beyond’ article. No significant association of fluoride exposure with IQ in high school or cognition as assessed at multiple points in later life.”
The study, “Childhood fluoride exposure and cognition across the life course,” was authored by John Robert Warren, Gina Rumore, Soobin Kim, Eric Grodsky, Chandra Muller, Jennifer J. Manly, and Adam M. Brickman.
