A comprehensive study conducted by researchers at the University of Minnesota has revealed that fluoride levels commonly found in drinking water do not negatively affect cognitive function. In fact, the research indicates that exposure to these levels might actually enhance cognitive abilities over time. This groundbreaking analysis, which spans over four decades, is the largest of its kind in the United States.
The study examined fluoride exposure and cognitive outcomes in a cohort of 26,820 individuals selected from the 1980 High School and Beyond cohort study. This cohort originally comprised 58,270 students from 1,020 American high schools. Participants were reinterviewed multiple times until 2021, allowing researchers to gather extensive data on cognitive performance linked to fluoride exposure in drinking water.
To assess the impact of fluoride, researchers matched academic data with student locations and the fluoridation status of those areas, utilizing data from the US Department of Health and Human Services’ Fluoridation Census, which covers the years 1967 to 1993. Additionally, they referenced data from the US Geological Survey, which characterized fluoride levels in untreated groundwater from 38,105 wells measured between 1988 and 2017.
The findings indicate that children exposed to recommended fluoride levels—ranging from 0.7 mg/liter to 1.2 mg/liter between 1962 and 2015, and 0.7 mg/liter from 2015 to present—scored higher in various cognitive assessments, including vocabulary, reading, and math, by their final school year. This cognitive advantage persisted into middle age, although the results were not statistically significant.
“This is a great example of understanding the data and scientific research used to draw conclusions,” said Gina Rumore, one of the study’s authors at the Life Course Center. “While extremely high levels of fluoride can be toxic, fluoride in drinking water at recommended levels is not harmful. It provides substantial oral health benefits and now appears to correlate with better cognitive performance.”
The debate surrounding fluoride in drinking water has been contentious for decades. Earlier this year, the US Department of Health and Human Services proposed removing fluoride from municipal supplies. Some states, including Utah and Florida, have already eliminated fluoride, while other states have varying levels of access to fluoridated public water. A 2024 investigation by US News & World Report reported that less than half of residents in ten additional states have access to fluoridated water.
Fluoride’s introduction into public water systems began in Grand Rapids, Michigan, in January 1945, following studies that demonstrated its effectiveness in reducing tooth decay. Despite its documented benefits, fluoride has faced significant opposition, often fueled by misinformation from smaller studies conducted in countries with much higher fluoride levels than those typically found in the US. Notably, a study linking fluoride exposure to lower IQ has since been discredited.
“It is vitally important for the public – and policymakers – to know there is no credible scientific evidence supporting the claim that fluoridating municipal water at recommended levels harms children’s IQ,” stated John Robert Warren, another author of the study. “In fact, the opposite appears to be true.”
The researchers conducted supplementary analyses to consider other variables, such as community differences in fluoride exposure. They found consistent patterns in cognitive outcomes among those who remained in the same community versus those who moved during their schooling. Additionally, they highlighted that municipalities that fluoridate their water often invest in other areas, such as education and healthcare, which may contribute to improved cognitive outcomes.
Despite the study’s significant findings, the researchers acknowledged limitations, including incomplete historical data on panelists’ residences and the reliance on proxy measures for fluoride consumption. They noted the need for more comprehensive information on fluoride exposure throughout the adult lifespan.
Nevertheless, they concluded that fluoride levels typical in the United States correlate with better cognitive outcomes during adolescence and do not harm cognitive function later in life. Fluoride toxicity, which can lead to fluorosis, generally occurs in regions with fluoride levels far exceeding the recommended 0.7 mg/liter outlined by the US Centers for Disease Control and Prevention.
“Our findings reinforce that community water fluoridation is a safe and effective public health measure,” said Matthew Hobbs, an Associate Professor at the University of Canterbury in New Zealand. He emphasized that concerns regarding fluoride and cognition largely stem from studies of populations exposed to much higher fluoride levels, not from fluoridated community water.
The health benefits of fluoride for dental care have been well-established over decades of research. “This research is refreshing, particularly because of its extensive duration and the litigious environment in the United States,” noted Justin Wall from Te Rōpū Niho Ora (Oral Health New Zealand). “It demonstrates that fluoridation is safe for all ages, especially as the population ages and retains more teeth.”
The study, encompassing both extensive historical analysis and contemporary data, was published in the journal Science Advances. It adds a vital perspective to the ongoing discourse surrounding fluoride in drinking water and its implications for public health.
