Fluoride Study Claiming No Effect on IQ Has ‘Basically No Connection to Reality,’ Critics Say
By Brenda Baletti, Ph.D.
Post on May 15, 2025
Mainstream media are widely promoting a study claiming that community water fluoridation has no effect on IQ, but critics told The Defender the study contains fundamental methodological errors that invalidate the authors’ conclusions. The Defender asked to be included in a media call with the study’s author, but was denied access.
Experts who analyzed a recent study claiming that fluoride exposure from drinking water doesn’t affect IQ told The Defender the study was deceptive and relied on a flawed methodology.
The “highly anticipated long-term study,” published April 13 in Proceedings of the National Academy of Sciences (PNAS), was widely cited by media and proponents of water fluoridation as evidence that there is no difference in IQ between people who drank water containing fluoride at the level currently recommended by U.S. public health agencies and people who didn’t.
But Chris Neurath — a research director for the American Environmental Health Studies Project who analyzed the study — identified flaws in the data used for the study and the authors’ conclusions.
Neurath said that one of the “most deceptive parts” of both the media coverage and the study itself was the claim that it studied community water fluoridation, and that it was a comparison between two groups — people exposed to fluoridation and people who weren’t.
Neurath found that the authors didn’t actually measure how much fluoride study participants consumed.
They also didn’t study people who were exposed to fluoride as neonates or young children — the very groups that research shows are most affected by fluoride exposure.
For example, the researchers used data from the Wisconsin Longitudinal Study, which tracked about 10,000 people in the 1957 Wisconsin high school graduating class. Participants took IQ tests in high school and cognitive tests later in life — at ages 53, 64, 72 and 80.
That means the study participants were born in about 1939 — six years before community water fluoridation began anywhere in the U.S.
Given that community water fluoridation didn’t even exist when the study participants were born, no one in the study was exposed to it during the critical developmental years when it can affect IQ — and few people were exposed to fluoridated water at all.
Attorney Michael Connett, who represents plaintiffs in the landmark lawsuit against the U.S. Environmental Protection Agency that put concerns about water fluoridation on the national radar, criticized the study in a post on X.
He wrote:
“The study’s use of a clearly erroneous measurement of early life exposure to fluoridated water made it virtually impossible for this study to detect an association between early-life fluoride exposure and IQ.
“It’s like trying to determine if prenatal exposure to Tylenol is associated with autism by determining the Tylenol use of the child’s neighbor rather than the child’s mother.”
‘Very faulty’ exposure method ‘invalidates the entire study’
Neurath and Connett also criticized the PNAS study’s choice of wells to estimate fluoride exposure.
The researchers assumed that if a Wisconsin county had a single well found to have naturally elevated levels of fluoride at the currently recommended 0.7 milligrams per liter (mg/L), then everyone in the county was exposed to that level of fluoride.
Connett said that assumption, at the heart of the study, “has basically no connection to reality” because fluoride levels in a single well can’t provide information about fluoride in other wells, “let alone ‘all’ wells.”
The researchers identified the wells using U.S. Geological Survey data collected between 1988 and 2017, which contained information on about two wells per county in Wisconsin.
Neurath compared the data used by the study authors to data on more detailed studies on well fluoridation from the state of Wisconsin — data that the authors of the PNAS study didn’t use.
He found that most of the counties included in the new study had only one well containing fluoride at 0.7 mg/L, and that some had up to 30 wells with levels measuring well below that threshold.
In one example from Sheboygan County, Neurath found that the single well identified as containing fluoride wasn’t even a drinking water well — it was a “monitoring well” next to an agricultural field. All other wells tested in the county had fluoride levels ranging from 0 to 0.2 mg/L.
Neurath said that most Wisconsin residents weren’t even getting water from private wells — they relied on public water systems. At the time, about 3% of public water systems had naturally high levels of fluoride.
He concluded that the study used “a very faulty exposure measure,” which he said, “invalidates the entire study.”
Lead author denies Defender access to reporter call, deflects scrutiny
Researchers from the University of Minnesota, the University of Wisconsin and the University of Michigan conducted the PNAS study.
Lead author Rob Warren, Ph.D., was scheduled to speak with reporters on Tuesday in 15-minute slots to promote the study. The Defender signed up but was denied access. At least one local news station interviewed Warren that day.
Warren, a sociologist, told reporter Connor Rhiel that concerns about fluoride and IQ typically draw on research from small communities in Iran and China with abnormally high fluoride levels for “weird geological reasons” — and weren’t relevant to U.S. policy.
He said his team chose their approach because large cohort studies tracking fluoride exposure and cognitive outcomes over time are “relatively rare” and difficult to conduct.
He did not mention the major North American cohort studies — published in top journals and most often cited by fluoride critics — already conducted in the U.S., Canada, and Mexico, which identified the link.
Warren said his research shows that children drinking optimally fluoridated water have nothing to fear for their cognition or IQ.
In a similar paper published last year — which critics also flagged for lacking any measure of fluoride exposure during gestation or infancy — he went further, claiming fluoride provided a cognitive benefit, a claim that drew sharp criticism.
When the local reporter asked whether this study found any benefits from fluoride exposure, Warren didn’t mention them. Instead, he offered general remarks that fluoride is good for teeth.
The Defender submitted its intended interview questions to Warren via email Tuesday, asking him to explain and justify the study’s assumptions about fluoride exposure.
Warren had not responded as of press time today.
