New Research Shatters Common Claim About Fluoride and Intelligence

The case for removing fluoride from the drinking water supply just got weaker. Research out today shows no link between water fluoridation and declining cognition in children or adults.

Researchers examined the education and medical records of a large, nationally representative group of Americans. They found no evidence that water fluoridation was associated with lower test scores in high school or lower cognition scores later in life. The findings seem to undermine one of the most common arguments made against adding fluoride to people’s drinking water, the researchers say.

“If fluoride lowers your IQ, then we should see lower test scores in places where they fluoridate the water. And we didn’t, at all,†lead author John Warren, a sociologist and demographer at the University of Minnesota’s Minnesota Population Center, told Gizmodo.

The fluoride bogeyman

Among some groups, water fluoridation has long been blamed for a range of health problems.

Longtime antiscience crank Robert F. Kennedy Jr. has argued that fluoride is causing widespread IQ loss and increased bone cancer, for instance. And since taking over as the U.S. Secretary of Health and Human Services under the second Trump administration, Kennedy has stated that he will tell the CDC to no longer recommend water fluoridation on a national level.

Many of the most boisterous claims made about fluoride are unsubstantiated by the current data, including a supposed cancer risk. That said, there has been a more substantial scientific debate over whether water fluoridation can affect children’s IQ. A review published earlier this January and conducted by scientists at the National Institutes of Health found a possible link between lower IQ levels in children and greater fluoride exposure, for example.

Study researcher John Warren notes, as others have, that this review largely focused on studies looking at much higher and potentially toxic levels of fluoride exposure than typically seen in the U.S., however. And in general, there’s only been limited research examining this possible link among American children.

“It really struck me that there was a problem with that meta-analysis,†Warren said.

A lack of harm

Warren and his colleagues believed they had access to data that could provide a clearer picture of the relationship between fluoride and cognition: the High School and Beyond study. This project, initiated in the 1980s, collected reading, math, and vocabulary test scores from over 26,000 high school students across the country; a subset of surviving participants were also contacted as adults and asked to undergo medical evaluations, including tests of their cognition, up through age 60.

Many people grow up in the towns and neighborhoods where they went to high school, especially in the 1980s. So the researchers cross-referenced other federal data on water fluoridation levels in the areas where the children went to school. This data was then used as a proxy for people’s exposure to fluoride as they were growing up. Though many parts of the U.S. had started regularly fluoridating their water by the early 1980s, plenty hadn’t or had adopted their own local standards, allowing the researchers to compare varying levels of fluoride exposure among neighborhoods.

All in all, Warren’s team failed to find a negative association between relatively higher levels of fluoride in a town’s drinking water and high school children’s test scores; if anything, kids in the U.S. exposed to fluoridated water actually seemed to have slightly higher scores on average. This slight advantage faded by age 60, but the researchers still found no link between lower cognition in adults and fluoridated water exposure in childhood. They also found that few neighborhoods exceeded recommended fluoride levels.

“If [fluoride] lowers your IQ, which is supposed to be a permanent change, then you would expect lower cognition at age 60. But we didn’t find that,†Warren said.

The team’s findings were published Wednesday in Science Advances.

The future of fluoridation

Warren notes this study only looked at the relationship between cognition and fluoride, so it alone can’t tell us whether water fluoridation is a net positive. But he points out that other research has affirmed its benefits in improving dental health.

The researchers are also aware that children’s test scores are an imperfect indicator of IQ. But they’re now conducting a similar study of children in Wisconsin, where they do have access to IQ test scores.

As is, these findings obviously undercut the rationale to remove fluoride from people’s drinking water. And while the researchers are planning to further study the topic, they argue it will take much stronger evidence than currently amassed to reasonably justify such a removal based on hypothetical concerns about IQ.

“What we’re showing is that this IQ story—it doesn’t hold up in the United States in a representative sample at levels of fluoride that are actually relevant for policy discussion,†Warren said.

Unfortunately, reason is in short supply these days. Aside from RFK Jr.’s federal campaign, Florida and Utah have already passed legislation this year to ban water fluoridation, and still more states and towns may soon follow.

Fluoride might not be lowering anyone’s IQ. But the fear of it sure seems to be doing a number on some people’s brains.