There is no evidence that adding low levels of fluoride to community drinking water affects children's IQ or brain function later in life, according to a new study that tracked more than 10,000 people from their teen years through to old age.
In many regions of the world, fluoride is added to water to improve communities' dental health: it's proven to strengthen teeth and reduce decay.
The new study, which draws on longitudinal data from 10,317 high school seniors from 1957 to 2021, when participants were 80, finds no association between community water fluoridation exposure and IQ, or other measures of cognitive function later in life.
Most health authorities agree that fluoridation is safe at levels found in most community water in the US.
But in 2025, a widely misinterpreted paper found that exposure to high doses of fluoride, well above the 0.7 mg/L recommended by the US Public Health Service, may be associated with lower IQ in children.
Skeptics, however, were quick to point out that the data used for this review are of poor quality and provide no reason to worry about fluoride in US drinking water.
Some states in the US, including Utah and Florida, have already banned community water fluoridation.
The 2025 paper mainly reviewed studies conducted in China and India. No studies from the US were available. The studies also did not control for contaminants in water.
"Utah, Florida, and many municipalities have chosen to remove fluoride from drinking water based on flawed studies that considered the IQ effects of exposure to massive doses of fluoride," says the lead researcher on the new paper, sociologist and demographer John Robert Warren from the University of Minnesota.
"Because levels of fluoride added to municipal drinking water in the US are so much lower, almost all prior evidence from those international studies is not relevant to US public policy debates."
Even the 2025 study acknowledged its limitations regarding lower levels of community water fluoridation, such as those seen in the US. This gap is something the new research aims to remedy.
Warren worked with a team of researchers from across the US to gain a clearer picture of the fluoride-IQ relationship in the US by bringing together data from the Wisconsin Longitudinal Study.
This included the IQ scores of 10,317 graduating students in 1957, along with their home addresses, which could be paired with historical records of fluoride content in water to approximate exposure.
Estimates of fluoride consumption based on water supply aren't as accurate as direct measurements from urine samples, especially since tap water isn't the only fluoride source in our lives: food, toothpaste, and other consumables could make a big difference to an individual's real fluoride exposure.
But until further research is conducted, this is one of the most robust studies carried out in the US context.
Some of these children grew up drinking well water, while others drank from the community supply. Historical records of these water sources – and when fluoridation programs began – enabled a kind of natural study, with some students exposed earlier than others.
At ages 53, 64, 72, and 80, these former Wisconsin high school students were tested on their cognitive abilities, providing scientists with nearly 70 years' worth of data to work with. These check-ins also gave them updated addresses, improving the accuracy of their fluoride exposure estimates.
Gina Rumore, a researcher at the University of Minnesota and co-author on the new paper, says the results "provide no support for the claim that community water fluoridation has any harmful effect on children's IQ or on adult cognition."
After adjusting for all available confounders, there was no evidence that students performed worse (or better) than their peers if they were exposed to fluoride through community water programs. This held out well into old age.
It replicates the results of a study that Warren and Rumore led in November 2025, which instead drew on cognitive test results from the US High School and Beyond cohort, and similarly found no significant association with water fluoridation.
That study actually found children exposed to the recommended levels of fluoride in drinking water had modestly better cognitive performance in their younger years – though by age 60, that benefit had disappeared.
What's more, other studies have found that poor dental health (the kind that water fluoridation can protect against) is linked to cognitive decline.
Based on a case study in Alaska, dental health can plummet quickly after community water fluoridation programs stop.
Related: The Cause of Alzheimer's May Be Coming From Within Your Mouth
Whether this new study can undo the damage from widespread misinterpretation of existing observational studies remains to be seen.
Meg Lochary, a pediatric dentist from Union County in North Carolina (a county that ended fluoridation in 2024), told NBC's Erika Edwards and Kaan Ozcan: "I've never seen as much pushback to fluoride as I have in these last few years."
This is despite support from major public health groups, including the CDC, the American Dental Association, and the American Academy of Pediatrics, for community water fluoridation programs.
The research is published in Proceedings of the National Academy of Sciences.