Intelligence and brain function tests gave the same results whether or not people consumed fluoridated water while growing up, a long-awaited long-term study has concluded.
This new research, published on Monday in the prestigious journal Proceedings of the National Academy of Sciencesis the first to measure exposure to community water fluoridation during childhood in the United States, as well as its potential impact on cognition through age 80.
The results contradict claims made by Health Secretary Robert F. Kennedy Jr., who maintained that fluoride is an “industrial waste” associated with IQ loss.
Scott Tomar, head of the Department of Population Oral Health at the University of Illinois at Chicago, called the new study “pretty significant.”
“I think the public can rest assured,” said Tomar, who was not involved in the new investigation. “There is no association between community water fluoridation and any measure of IQ or neurodevelopment.”
Fear of a possible link to lower IQ scores has been the argument put forward by a growing number of communities across the country to ban the addition of fluoride to drinking water.
Two states — Utah and Florida — have enacted bans on the matter. Several other states, including Kentucky, Louisiana, Missouri and Oklahoma, have similar bills pending passage.
Opponents of water fluoridation often cite smaller studies that suggested a possible link between this mineral and children’s IQ. These studies were conducted in China or other countries where fluoride concentrations are much higher than those allowed in the United States.
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The optimal level of fluoride in drinking water to prevent cavities is 0.7 milligrams per liter, according to the Centers for Disease Control and Prevention (CDC). This is equivalent to just 3 drops in a 55 gallon barrel. The legal limit for fluoride in drinking water in the United States is 4.0 milligrams per liter.
The lack of high-quality data was what motivated this new research, led by Rob Warren, a sociologist and population health expert at the University of Minnesota.
Theirs is the first robust study conducted in the United States on the possible effects of water fluoridation on intelligence and brain capacity, spanning from adolescence to late adulthood.
It used data from the Wisconsin Longitudinal Study, which has followed 10,317 people in that state since they graduated from high school in 1957.
Participants took IQ tests at age 16 and subsequently underwent cognitive testing later in life: at ages 53, 64, 72, and 80.
The original purpose of the data was not to analyze fluoride; Therefore, Warren’s team did not have urine or blood tests to measure the exact fluoride levels in individuals. They estimated exposure based on records of when community water fluoridation began in certain areas, as well as the location of untreated water wells.
“I was curious about the short-term effects on cognition during adolescence, but also about cognitive functioning later in life. Because if there are negative consequences for IQ in early life, you would expect these to have long-term effects,” Warren said.
His team found no differences, at any stage of life, between people who grew up with water fluoridation in Wisconsin and those who did not. Since 1995, 86 Wisconsin communities have stopped adding fluoride to their municipal water systems, according to data from the state Department of Natural Resources.
This new research builds on a study published by Warren in December 2025, which also found no links between community water fluoridation early in life and the results of brain function tests performed at age 60.
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Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada, said Warren’s latest research is “one of the most rigorous attempts to date to examine the relationship between fluoridation and cognition across the lifespan.”
Lanphear published a study in 2019 in which it was observed that IQ levels were slightly lower in 3- and 4-year-old children whose mothers had higher levels of fluoride in their urine during pregnancy.
The new study has one limitation: The researchers did not measure the exact amount of fluoride each individual consumed, as Lanphear noted in an email.
“Exposure is inferred from place of residence,” Lanphear wrote. “Nor can it account for total intake from sources such as infant formula, toothpaste or diet. If you don’t measure individual exposure, you risk missing the real signal.”
Warren said her studies should not be interpreted as the final word on the matter, but rather should prompt additional research. “There are now good reasons to doubt the claim that fluoride causes a reduction in IQ.”
More recently, the Trump Administration has stopped demonizing fluoride. In March, Jay Bhattacharya, who currently heads the CDC, told a House Appropriations subcommittee that “fluoride is essential for oral health,” although he maintained that too much fluoride “can have neurological and developmental repercussions.”
However, the issue has already caused panic among some families who now refuse to allow their children to receive fluoride treatments in dental offices.
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“I’ve never seen more resistance to fluoride than in recent years,” said Meg Lochary, a pediatric dentist in Union County, North Carolina. Union County suspended water fluoridation in 2024. “People are very, very leery about it.”
Water fluoridation has been hailed as one of the most notable public health initiatives of the last century for its ability to combat tooth decay.
Leading public health groups—including the American Dental Association, the American Academy of Pediatrics, and the CDC—support the use of fluoridated water. They all cite studies showing that it reduces tooth decay by 25%.
“One of the main reasons children miss school is toothache,” Tomar said. “In more serious cases, the problem can lead to an infection that then spreads to other parts of the body.”
Susan Fisher-Owens, a professor of pediatrics and of preventive and restorative dental sciences at the University of California, San Francisco, said a growing body of research is revealing links between poor oral health and chronic diseases that develop later in life, such as diabetes and dementia.
Adding fluoride to community water supply systems is a “safe, low-cost way to help protect people,” he said.
