Tests of intelligence and brain function showed the same results whether or not people drank fluoridated water growing up, a highly anticipated, long-term study found.<\/p>\n\n\n\n
The new research, published Monday in the respected Proceedings of the National Academy of Sciences, is the first to measure community water fluoridation exposure during childhood in the U.S. and any potential impact on cognition up to age 80. The results contradict claims made by Health Secretary Robert F. Kennedy Jr. that fluoride is \u201cindustrial waste\u201d associated with IQ loss.<\/p>\n\n\n\n
Dr. Scott Tomar, head of the department of population oral health at the University of Illinois in Chicago, called the new study \u201cquite significant.\u201d<\/p>\n\n\n\n
\u201cI think that the public can be assured,\u201d Tomar, who was not involved with the new research, said. \u201cThere is no association with community water fluoridation and any measure of IQ or neurodevelopment.\u201d<\/p>\n\n\n\n
Fear over a link to lower IQ scores has been cited by a growing number of communities across the country that prohibit the addition of fluoride to drinking water. Two states \u2014 Utah and Florida \u2014 have enacted bans. Several other states, including Kentucky, Louisiana, Missouri and Oklahoma, have similar legislation pending.<\/p>\n\n\n\n
Opponents of water fluoridation have often pointed to small studies that suggested a possible link between the mineral and kids\u2019 IQ. Those studies were conducted in China or other countries with much higher fluoride concentrations than allowed in the U.S.<\/p>\n\n\n\n
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. That amounts to 3 drops in a 55-gallon barrel. The legal limit in U.S. drinking water is 4.0 milligrams per liter.<\/p>\n\n\n\n
The lack of high-quality data prompted the new research from Rob Warren, a sociologist and population health expert at the University of Minnesota. His is the first robust U.S.-based study of water fluoridation\u2019s possible effects on intelligence and brain power from the teen years into older adulthood.<\/p>\n\n\n\n
He used data from the Wisconsin Longitudinal Study that\u2019s followed 10,317 people in the state since they graduated from high school in 1957. Participants took IQ tests at age 16, then did cognitive testing later in life, at ages 53, 64, 72 and 80. The original purpose of the data wasn\u2019t to look at fluoride, so Warren\u2019s team didn\u2019t have urine or blood tests to measure exact levels of fluoride. They estimated their exposure based on records of when community water fluoridation began in certain areas, and on locations of untreated wells.<\/p>\n\n\n\n
\u201cI was curious about the short-term effects on adolescent cognition,\u201d Warren said, \u201cbut also cognitive functioning later in life. Because if there\u2019s negative consequences for early life IQ, you might expect long- term effects.\u201d<\/p>\n\n\n\n
His team found no difference, 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 municipal water systems, according to the state\u2019s Department of Natural Resources.<\/p>\n\n\n\n
The new research builds on research Warren published in December 2025, which found no link between community water fluoridation in early life and tests of brain function at age 60.<\/p>\n\n\n\n
Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada, said Warren\u2019s latest research is \u201cone of the more rigorous attempts to examine fluoridation and cognition across the life course.\u201d Lanphear published a 2019 study that found IQ levels to be slightly lower in 3- and 4-year-old children whose mothers had higher measures of fluoride in their urine while pregnant.<\/p>\n\n\n\n
There is a limitation in the new study: The researchers didn\u2019t measure how much fluoride individuals actually consumed, Lanphear wrote in an email.<\/p>\n\n\n\n
\u201cIt infers exposure from place of residence,\u201d Lanphear wrote. \u201cIt also cannot account for total intake from sources such as infant formula, toothpaste, or diet. If you don\u2019t measure individual exposure, you risk missing the real signal.\u201d<\/p>\n\n\n\n
Warren said his studies shouldn\u2019t be interpreted as the final word on the matter, and should prompt additional research. \u201cThere\u2019s now good reason to doubt the claim that fluoride causes reduction in IQ.\u201d<\/p>\n\n\n\n
More recently, the Trump administration has backed off demonizing fluoride. In March, Dr. Jay Battacharya, who is currently leading the CDC, told a House Appropriations subcommittee that \u201cfluoride is essential for oral health,\u201d although he maintained that too much \u201ccan have neurological and developmental impacts.\u201d<\/p>\n\n\n\n
But the issue has already instilled panic in some families who now refuse to allow their children to be treated with fluoride in dentist offices.<\/p>\n\n\n\n
\u201cI\u2019ve never seen as much pushback to fluoride as I have in these last few years,\u201d Dr. Meg Lochary, a pediatric dentist in Union County, North Carolina, said. Union County stopped water fluoridation in 2024. \u201cPeople are very, very wary of it.\u201d<\/p>\n\n\n\n
Water fluoridation has been heralded as one of the top public health initiatives of the last century for its ability to fight cavities.<\/p>\n\n\n\n
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%.<\/p>\n\n\n\n
\u201cOne of the main reasons kids miss school is because of toothaches,\u201d Tomar said. \u201cIn the most severe cases, it can proceed to become an infection that then spreads to other parts of the body.\u201d<\/p>\n\n\n\n
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 is showing links between poor oral health and chronic diseases that develop later in life, like diabetes and dementia.<\/p>\n\n\n\n
The addition of fluoride in community water systems is a \u201clow-cost, safe way to help protect people,\u201d she said.<\/p>\n\n\n\n