RFK Jr. said fluoride makes kids ‘stupider,’ and a new study followed over 10,000 Americans to find out

For years, the question of whether fluoride in drinking water harms children’s intelligence has been a flashpoint in American public health. Health and Human Services Secretary Robert F. Kennedy Jr. argued in 2025 that fluoride makes children “stupider,” a claim that a new large-scale study, built on decades of American health data, directly addresses.

A new study published April 13 in the

Proceedings of the National Academy of Sciences

tracked 10,317 people from Wisconsin who graduated high school in 1957, following them from adolescence into their 80s. Participants took IQ tests at age 16, then completed standardized cognition tests at ages 53, 64, 72, and 80, tracking whether fluoride exposure in childhood had any lasting effect on how people think and reason into old age.

The study, led by University of Minnesota sociologist and population health expert Rob Warren, found no difference in cognitive performance at any stage of life between people who grew up drinking fluoridated water and those who did not. Warren said the data let him ask whether children exposed to fluoride had lower IQ scores, and the answer, he noted, was clearly no.

How the Study Was Built, and What It Could Not Measure

Participants were sorted by when they were first estimated to have had regular exposure to fluoridated water, from birth, age 8, or age 14, based on historical records of when community water fluoridation began in their areas. Researchers also accounted for residents on private wells that were not fluoridated, giving the study a built-in point of comparison within the same state.

The study has a notable limitation: fluoride exposure was inferred from residential records rather than measured directly in blood or urine. Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada who published a 2019 study suggesting slightly lower IQ in young children of mothers with higher fluoride levels during pregnancy, said Warren’s study cannot fully account for fluoride intake from sources like toothpaste, infant formula, or diet.

Warren acknowledged as much, saying his work should not be treated as a final word on the subject and should encourage more research. Still, Dr. Scott Tomar, head of the department of population oral health at the University of Illinois Chicago, called the study “quite significant,” adding that the public can be assured there is no association between community water fluoridation and any measure of IQ or neurodevelopment.

The Debate Behind the Headlines: Fluoride, Policy and Past Studies

At an April 2025 cabinet meeting, Kennedy praised Utah for becoming the first state to ban local governments from adding fluoride to public water and said he was working to change federal fluoride regulations, claiming that higher fluoride exposure leads to lower intelligence. Those statements drew on a body of smaller studies that have been criticized by the American Dental Association and the National Academies of Sciences, Engineering, and Medicine for methodological shortcomings.

Warren has pointed out that the studies most frequently cited by fluoride opponents largely compared children exposed to very high fluoride concentrations in countries like China, India, and Iran, levels far above the 0.7 milligrams per liter that is considered optimal in the U.S. and well below the EPA’s legal ceiling of 4.0 milligrams per liter. The policy debate in America, he noted, is about recommended levels versus no fluoride at all, not about comparing extreme doses.

More recently, the Trump administration has shifted its tone on the issue. In March 2026, acting CDC director Dr. Jay Bhattacharya told a House Appropriations subcommittee that fluoride is “essential for oral health,” while adding that too much can have neurological and developmental impacts. The 2022 CDC data showed that 72.3% of Americans on community water systems received fluoridated water, a figure consistent with previous years.

What This Means for Public Health, and Why the Debate Is Still Unfolding

Fluoride has been added to U.S. community water since 1945, when Grand Rapids, Michigan, became the first city to fluoridate its supply. Major public health organizations, including the American Dental Association, the American Academy of Pediatrics, and the CDC, support its continued use, citing evidence that it reduces tooth decay by about 25%. Severe tooth decay remains one of the leading reasons children miss school, and in serious cases can spread beyond the mouth.

Despite the new research, concern has already taken hold in some communities. Pediatric dentist Dr. Meg Lochary, who practices in Union County, North Carolina, which stopped fluoridating its water in 2024, said she has seen more pushback against fluoride in recent years than at any other point in her career. Several states, including Utah, Florida, North Dakota, Tennessee, and Montana, have passed or are considering legislation to ban or limit fluoride in public water systems.

Warren’s study builds on earlier research he published in December 2025, which also found no link between early-life fluoride exposure and cognitive test results at age 60. Together, the two studies represent the most sustained American look at the question to date. Whether they settle the debate in practice, among policymakers, parents, and local governments already acting on concerns, remains a separate question that the science alone may not resolve.