In the first US study looking at whether the recommended fluoride levels in drinking water affects brain function, researchers have found that the hot-button mineral has no negative impacts on cognition – and may actually be giving it a boost.
University of Minnesota scientists investigated fluoride exposure and cognitive outcomes in individuals from childhood to middle life, spanning just over 40 years – a first-of-a-kind study for scope and longevity. A subset of 26,820 individuals from the 1980 High School and Beyond cohort study was randomly selected out of the total 58,270 sophomores and seniors surveyed at 1,020 American high schools and were reinterviewed numerous times through 2021.
The researchers then matched this academic data with student location and the fluoridation status in those places, taken from the US Department of Health and Human Service’s Fluoridation Census (1967 to 1993). They also sourced US Geological Survey data that characterized fluoride levels in untreated groundwater, measured in 38,105 wells between 1988 and 2017. The team also accounted for the change in fluoridation guidelines, which nearly halved recommended levels in 2015.
What they found was that kids who had been exposed to recommended levels of fluoride in drinking water – 0.7 and 1.2 mg/liter between 1962 and 2015, and 0.7 mg/L from 2015 to present – had, on average, higher scores across the board by their final school year. They came out on top in vocabulary, reading and math.
The advantage, the researchers noted, continued through life until some participants were aged 60, however, the results were not statistically significant.
“This is a great example of understanding the data and scientific research used to draw conclusions,” says Gina Rumore, one of the study's authors at the Life Course Center. “While extremely high levels of fluoride like we see in some parts of the world can be toxic, fluoride in drinking water at recommended levels is not. Fluoridating drinking water is known to have massive oral health benefits, and now it appears that it also leads to better – not worse – cognitive test performance.”
Fluoride in drinking water has been a heated topic for decades, and earlier this year the US Health and Human Services tabled its intention to have it removed from local government supplies. While Utah and Florida have cut fluoride completely, that doesn't mean the other 48 have full access. A 2024 investigation by US News & World Report found that there are 10 additional states where less than half of the residents accessing public water supplies had fluoride coming out of the faucet.
Why fluoride divides people is complicated. It was first rolled out in Grand Rapids, Michigan, in January 1945, after evidence showed that having a trace amount in water could dramatically lower tooth decay and cavities. But this "compulsory medication" received a great deal of pushback, and it became the most damaging dentistry "scare" to this day. Then, a handful of smaller and non-representative studies looking at kids in China, India and Iran who had experienced poor health outcomes after ongoing exposure to high levels of fluoride only fueled misinformation campaigns. Except the level of fluoride those respective cohorts were exposed to was many times that of anyone in the US. And one such study, which we covered, linking fluoride to low IQ, has been discredited in the years since.
“It is vitally important for the public – and people who influence public policy – to know that there is absolutely no credible scientific evidence to support the claim that putting fluoride in municipal drinking water at recommended levels harms children’s IQ," said study author John Robert Warren. “It In fact, the opposite appears to be true.”
The researchers also completed two supplementary analyses to account for variables like students who lived in different communities – either with or without fluoride. When they analyzed those who remained in the same community for their entire school life, as well as children who had moved around, they saw the same pattern as the overall cohort.
They also tried to separate the biological impact of fluoride and the social, cultural, economic and political aspects that may have influenced local governments to introduce treated water.
"Municipalities that fluoridate their water may also be places that make other investments – in education, housing, healthcare, etc – that lead to better cognitive outcomes," the researchers noted.
There are limitations, of course.
"First, and most seriously, we would have preferred more complete information about where panelists lived from conception through late adolescence; we are forced to place them in the communities in which they went to secondary school," the researchers wrote. "Second, we would have preferred to know how much fluoride panelists consumed; instead, we proxy that with information about water chemistry. Especially given that the half-life of fluoride is just a few hours, this may be the only practical exposure measurement strategy in a community-based sample. Third, in estimating effects on adult cognition, we would have preferred to have information about fluoride exposures across the adult life course. Despite these limitations, our results provide strong evidence that exposure to fluoride – at levels ordinarily seen in the United States and of relevance to policy debates about municipal water fluoridation – has benefits for adolescent cognition and is, at worst, not harmful for later-life cognitive functioning."
Fluoride toxicity can lead to fluorosis, which can cause teeth to discolor and bone to deteriorate. However, scientific data on fluorosis has largely been gathered in regions where natural fluoride content in drinking water far exceeds what the US Centers for Disease Control and Prevention (CDC) outlines (0.7 mg/L). For example, India's groundwater has an average 2.37 mg/L of fluoride, and aa much as 9.22 mg/L in some areas.
While the study doesn't demonstrate that fluoride-treated water improves brain function, the researchers found a correlation. And, importantly, there was no link between fluoride and the prevalence of neurodevelopmental conditions seen in children and adolescents.
"This study provides important longer-term evidence that community water fluoridation is a safe and effective public health measure," said Associate Professor Matthew Hobbs from the University of Canterbury in New Zealand. "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.
"From a public health perspective, this matters," he continued. "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."
It's also worth pointing out that the dental health benefits of fluoride have been put beyond doubt over decades of research.
"It’s a refreshing piece of research, and in particular because it has gone on for such a long period of time, and it has gone on in a country that is profoundly litigious," noted Justin Wall from Te Rōpū Niho Ora (Oral Health New Zealand). "This research demonstrates that fluoridation is safe for all ages, and with the growing older population who have retained their teeth we need to protect their dentition as they age.
“The paper is entirely consistent with the information that has been gathered over many, many, many years of studying the fluoride supplementation of the domestic water supply," he added. "So, for this amount of research to be done over such a long period of time in America, I think it has to be taken seriously.
The research – paper one and paper two – was published in the journal Science Advances.
Source: University of Minnesota
