Decades of data tracking more than 10,000 Americans have produced a clear finding — and it runs counter to claims coming from inside the federal government.
What the Study Found
A long-term study published April 13, 2026 in the Proceedings of the National Academy of Sciences found no connection between drinking fluoridated water during childhood and any reduction in IQ or cognitive function — at any point in life, including up to age 80.
The research drew on data from the Wisconsin Longitudinal Study, which has followed more than 10,000 people since their senior year of high school in 1957. Participants took standardized IQ and cognitive tests at multiple stages of life. Across all measures — intelligence, memory, and overall brain function — researchers found no meaningful difference between those who grew up in communities with fluoridated water and those who did not.
According to NBC News, the study is the first of its kind in the United States to track community water fluoridation exposure during childhood and measure its potential impact on cognition across the full arc of a human life. That scope — tracking participants from their teens through their late seventies — gives the findings an unusual degree of longitudinal weight.
Why This Research Is Significant Right Now
The timing of the study’s publication is not incidental. Across the United States, a growing number of communities have moved to remove or restrict fluoride from public water supplies. The policy shift has been encouraged, in part, by statements from Health Secretary Robert F. Kennedy Jr., who has publicly described fluoride as “industrial waste” and linked its presence in drinking water to lowered IQ scores.
Those claims have reached a wide audience and influenced local water policy in multiple states. The new research published in PNAS directly addresses — and contradicts — the central premise of those claims.
Dr. Scott Tomar, head of the department of population oral health at the University of Illinois in Chicago, reviewed the new research and called it “quite significant.” He told NBC News: “I think that the public can be assured. There is no association with community water fluoridation and any measure of IQ or neurodevelopment.”
Dr. Susan Fisher-Owens, professor of pediatrics and preventive and restorative dental sciences at the University of California San Francisco, described the addition of fluoride to community water systems as a “low-cost, safe way to help protect people,” and noted that research increasingly shows links between poor oral health and chronic diseases that develop later in life, including diabetes and certain forms of dementia.
The Science Behind Community Water Fluoridation
The United States has practiced community water fluoridation since 1945. The practice involves adjusting the natural fluoride level in public water supplies to a concentration recommended by public health agencies as effective in preventing tooth decay.
Major public health organizations — including the American Dental Association, the American Academy of Pediatrics, and the Centers for Disease Control and Prevention — support community water fluoridation. Studies cited by these organizations indicate that fluoridated water reduces tooth decay by approximately 25 percent across all age groups.
According to Science News, lead researcher John Warren previously published a related analysis in November 2025, based on a nationally representative group of nearly 58,000 high schoolers surveyed in 1980 and followed over time, which also found no evidence that fluoride at levels typical of public water systems harms cognitive performance. The April 2026 study built on that earlier work with more precise IQ measurements and more detailed residential histories, creating a stronger evidentiary foundation.
Noted Limitations and the Path Forward
Researchers were transparent about one key limitation of the study. Rather than measuring how much fluoride individual participants actually consumed, the research inferred exposure based on where they lived. As Dr. Bruce Lanphear, a health sciences professor at Simon Fraser University, noted in correspondence with NBC News, this method cannot account for additional fluoride intake from sources like infant formula, toothpaste, or diet.
Lead researcher Warren was direct about what the study’s conclusions should and should not imply, saying the findings should not be read as the final word on the matter, and that the research should prompt additional scientific inquiry.
That measured tone is worth holding onto. The study does not claim that fluoride poses zero risk under any circumstances. It does provide the most detailed longitudinal evidence to date that fluoride at community water levels does not harm cognition in the populations it studied — and it does so with decades of data that simply did not previously exist in a single dataset.
What It Means for American Communities
For communities weighing decisions about their water supply, this research adds a substantive counterweight to the claims that have driven some localities away from fluoridation over the past several years.
The consequences of reducing or removing fluoride from public water are concrete. According to health researchers, one of the most direct effects of reduced fluoridation would be an increase in tooth decay — particularly among children and lower-income populations who have less access to preventive dental care. Dr. Tomar noted that one of the leading reasons children miss school is tooth pain, and that untreated dental infections can escalate into serious systemic health problems.
Whether the new research changes the trajectory of U.S. water fluoridation policy will depend on how public agencies, local officials, and federal health leadership respond to peer-reviewed evidence. What the study establishes is that on the specific question of fluoride and cognitive function, the science — now backed by a longitudinal dataset spanning seven decades — does not support the claims that have been driving policy in the other direction.
