Fluoride in drinking water has no effect on IQ or brain function, major study shows
Tests of intelligence and brain function showed the same results whether or not people drank fluoridated water growing up, according to a much-anticipated long-term study.
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The new research, published Monday in the respected journal Proceedings of the National Academy of Sciences, is the first to measure community exposure to water fluoridation during childhood in the United States and any potential impact on cognition up to age 80. The findings contradict Health Secretary Robert F. Kennedy Jr.’s claims that fluoride is an “industrial waste” associated with IQ loss.
Dr. Scott Tomar, chief of population oral health at the University of Illinois at Chicago, called the new study “pretty important.”
“I think the public can be reassured,” said Tomar, who was not involved in the new research. “There is no association with community water fluoridation and no measures of IQ or neurodevelopment.”
Fear of a link to lower IQ scores has been raised by a growing number of communities across the country that are banning the addition of fluoride to drinking water. Two states – Utah and Florida – have passed bans. Several other states, including Kentucky, Louisiana, Missouri and Oklahoma, have similar legislation pending.
Opponents of water fluoridation have often pointed to small studies suggesting a possible link between this mineral and children’s IQ. These studies were conducted in China or other countries with much higher fluoride concentrations than those allowed in the United States.
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. This is equivalent to 3 drops in a 55 gallon barrel. The legal limit for drinking water in the United States is 4.0 milligrams per liter.
The lack of high-quality data prompted Rob Warren, a sociologist and population health expert at the University of Minnesota, to launch new research. This is the first robust study in the United States on the possible effects of water fluoridation on intelligence and brain power from adolescence through adulthood.
He used data from the Wisconsin Longitudinal Study that followed 10,317 people in the state since they graduated from high school in 1957. Participants took IQ tests at age 16, then took cognitive tests later in life, at ages 53, 64, 72 and 80. They estimated their exposure based on records of the start of community water fluoridation in certain areas and the location of untreated wells.
“I was curious about the short-term effects on adolescent cognition,” Warren said, “but also on cognitive functioning later in life. Because if there are negative consequences on IQ early in life, you can expect long-term effects.”
His team found no difference at any stage of life between people who grew up with fluoridated water in Wisconsin and those who did not. Since 1995, 86 Wisconsin communities have stopped adding fluoride to municipal water systems, according to the state Department of Natural Resources.
The new research builds on the Warren study published in December 2025, which found no link between community water fluoridation in early life and brain function tests at age 60.
Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada, said Warren’s latest research constitutes “one of the most rigorous attempts to examine fluoridation and cognition across the lifespan.” Lanphear published a 2019 study that found IQ levels were slightly lower in 3- and 4-year-olds whose mothers had higher levels of urine fluoride during pregnancy.
There is one limitation in the new study: The researchers did not measure how much fluoride the individuals actually consumed, Lanphear wrote in an email.
“This infers exposure from place of residence,” Lanphear wrote. “It also can’t account for total intake from sources like infant formula, toothpaste or food. If you don’t measure individual exposure, you risk missing the real signal.”
Warren said his studies should not be interpreted as the final word on the issue and should prompt additional research. “There is now good reason to doubt the claim that fluoride causes a reduction in IQ.”
More recently, the Trump administration has backed away from demonizing fluoride. In March, Dr. Jay Battacharya, who currently heads the CDC, told a House Appropriations subcommittee that “fluoride is essential for oral health” while asserting that too much “can have neurological and developmental impacts.”
But the problem has already caused panic among some families who now refuse to allow their children to be treated with fluoride in dentist offices.
“I’ve never seen as much pushback against fluoride as I have in the last few years,” said Dr. Meg Lochary, a pediatric dentist in Union County, North Carolina. Union County stopped water fluoridation in 2024. “People are very wary of it. »
Water fluoridation has been considered one of the major public health initiatives of the last century due to its ability to combat cavities.
Major public health groups, including the American Dental Association, the American Academy of Pediatrics and the CDC, support the use of fluoridated water. All cite studies that show it reduces tooth decay by 25%.
“One of the biggest reasons kids miss school is because of toothache,” Tomar said. “In more severe cases, it can turn into an infection which then spreads to other parts of the body. »
Dr. Susan Fisher-Owens, professor of pediatrics and preventive and restorative dental sciences at the University of California, San Francisco, said a growing body of research shows links between poor oral health and chronic diseases that develop later in life, such as diabetes and dementia.
Adding fluoride to community water systems is “an inexpensive and safe way to help protect people,” she said.
