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.