RFK Jr. has tied fluoride with ‘stupider’ kids. What a new study says
People who drink fluoridated community water long-term are just as smart as those who don’t, a first-of-its-kind study found.
Published in the journal Proceedings of the National Academy of Sciences on Monday, April 13, the study is the first to test the impact of fluoridated water on cognition into late adulthood – long beyond childhood and adolescence, the usual targets of fluoride research. It expands upon previous research published in November 2025, also unique for being the first to analyze population-representative data from the United States up to the age of 60.
Community water fluoridation, or the act of adding the mineral to community water supplies to enhance dental health, has historically been considered a revolutionary accomplishment in public health, as noted by the Centers for Disease Control and Prevention. The practice has become a battleground in recent years, however, with Secretary of Health and Human Services Robert F. Kennedy Jr. saying in 2025, without evidence, that fluoride exposure makes children “stupider.” Oft-cited studies to this point have been questioned for their validity, especially those using data from outside the United States.
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“Like everybody else, I was intrigued by claims that there was a relationship between fluoride and IQ,” said study co-author Rob Warren, professor at the University of Minnesota. “And upon looking at the evidence, I was not impressed. The evidence used to support that claim was not great. And so I got to thinking, ‘well, what could we do with existing data on the U.S. that is population representative and actually considers fluoride at the levels that we care about?'”
Because of this, the study’s authors looked toward data from the Wisconsin Longitudinal Study, which followed 10,317 people from the state starting from when they graduated high school in 1957 throughout the rest of life. The authors reviewed results of standardized testing to measure the intelligence and mental function of these adults up to the age of 80, categorizing them by when they were first believed to have been regularly exposed to fluoridated water (from birth, age 8 or age 14) based on historical community records.
To take these measurements, researchers reviewed IQ tests administered to the participants in schools at the age of 16 and similar, standardized cognition examinations performed at ages 53, 64, 72 and 80.
Like the previous analysis it built upon, the study found no evidence that community water fluoridation is associated with lower adolescent IQ or cognition later in life.
“With (that information), I could answer the question, ‘Is it true that kids exposed to fluoride have lower IQ?’ And the answer is no, not at all,” said Warren. “And because those same people have been followed, they’re now in their 80s … I was able to also ask, ‘Is there any difference at any point in their lives in terms of their cognition?’ and the answer was no.”
While this study improved upon previous research by applying a finer-toothed comb to addressing confounding factors and following participants’ geographical movements throughout life, it has its own limitations – the biggest of which being that fluoride exposure was inferred based on community water records only, not complete, unique profiles for each individual.
Fluoride and how we use it in the US
Naturally occurring in water, soil, plants, rocks and even the air, fluoride was discovered as a useful tool for preventing cavities and tooth decay by the late 1930s. In 1945, Grand Rapids, Michigan, became the first city to fluoridate its community water, adjusting existing levels in the supply to the therapeutic 1.0 parts-per-million (ppm).
Since then, the levels have been adjusted to 0.7 ppm or 0.7 milligrams of fluoride per liter of water, which is considered optimal for preventing tooth decay. The maximum amount allowed in U.S. drinking water by the Environmental Protection Agency is 4.0 milligrams per liter.
The latest CDC data available from 2022 reported that 72.3% of the U.S. population on a community water source received fluoridated water, a percentage fairly consistent with 2020’s 72.7%. While the CDC maintains that fluoridated water is both safe and cost-effective, questions as to potential hazards introduced by water fluoridation have existed as long as the practice has been popular.
The potential for fluoride toxicity does exist, but would require consuming an amount of fluoridated water that would kill a human via water intoxication before the amount of fluoride could become harmful or deadly, according to the Cleveland Clinic.
“On a very personal level, there’s no reason to worry that your kid drinking the tap water that’s fluoridated is going to harm them, at least harm their neurocognitive development,” said Warren of current U.S. standards. “On a personal level, there’s much, much more important things to worry about than that.”
The growing anti-fluoride push
Kennedy has led a renewed charge against fluoridated water, saying in November 2024 that the second Trump administration would “advise all U.S. water systems to remove fluoride from public water,” citing unsubstantiated health concerns.
In an April 2025 cabinet meeting with President Donald Trump, Kennedy praised Utah for becoming the first state to prohibit local governments from adding fluoride to public water systems and said he was working to “change the federal fluoride regulations to change the recommendations.” He likewise claimed that “the more (fluoride) you get, the stupider you are, and we need smart kids in this country, and we need healthy kids.”
At this meeting and others, Kennedy and similar-minded anti-fluoride proponents have cited small studies that have shown mixed results regarding a potential link between fluoride exposure and IQ. These have been criticized by institutions like the American Dental Association and the National Academies of Sciences, Engineering and Medicine for using data from other countries outside the U.S., studying levels of fluoridation much higher than those allowed in the U.S., employing inadequate statistical rigor, and other methodological flaws.
“The bulk of (these studies) compare kids who are exposed to unbelievably high levels of fluoride to kids who are only exposed to ‘kind of’ high levels of fluoride in little villages in China or Iran or India, that are not at all representative of anybody outside of those villages,” Warren explained. “The policy question (in the U.S.) isn’t about toxic levels versus super toxic levels. That’s not what anybody’s talking about here, it’s about recommended levels versus nothing. And so most of the research really isn’t relevant because it’s about massive doses.”
Kennedy and the administration have somewhat pulled back on anti-fluoride messaging in 2026, with acting CDC head Dr. Jay Bhattacharya telling a House subcommittee in March that the mineral is “essential for oral health” before adding that too much can have “neurological and developmental impacts.”
Several states, including Utah, Florida, North Dakota, Tennessee and Montana, have passed or are considering bills banning or restricting the addition of fluoride to community water sources.
This article originally appeared on USA TODAY: RFK Jr. has tied fluoride with ‘stupider’ kids. What a new study says
