Long-term study finds no IQ link to community water fluoridation

A 10,317-person Wisconsin study put a hard limit on one of the loudest anti-fluoride claims in American politics: the idea that community water fluoridation lowers children’s intelligence. By following state testing records, city fluoridation histories and later-life cognitive testing, the researchers found no evidence that fluoridated water was linked to lower adolescent IQ or worse adult cognitive functioning.

The work drew on the Wisconsin Longitudinal Study, which followed a random sample of high school seniors who graduated in 1957 and tracked them through 2026. Researchers from the University of Minnesota, the University of Wisconsin and the University of Michigan matched where participants lived with the years their cities began fluoridating water, then compared those exposures with school test records and cognitive outcomes measured later in life, between ages 53 and 80. That design made the study stronger than much of the evidence cited in public fights over fluoridation, because it used a large U.S. sample and followed people across the life course rather than relying on isolated measures or high-exposure settings abroad.

The findings also directly challenged the body of research that critics of fluoridation have leaned on. Much of that earlier evidence came from studies of far higher fluoride exposure, often outside the United States. A 2024 JAMA Pediatrics review and meta-analysis of 74 studies found inverse associations between fluoride exposure and children’s IQ, but the Wisconsin researchers said those studies did not match the exposure levels typical in American community water systems.

That distinction matters because fluoridation has been one of the country’s longest-running public health tools. The Centers for Disease Control and Prevention says the practice began in 1945 in Grand Rapids, Michigan, and that it reduces tooth decay by about 25% in children and adults. The CDC also says tooth decay remains one of the most common chronic diseases among American children, and that one in four children living below the federal poverty level experiences untreated tooth decay. In 2022, more than 209 million people, or 72.3% of the U.S. population served by public water supplies, had fluoridated water.

The study lands amid a sharp political turn. Utah became the first state to ban fluoride additions to public drinking water in 2025, and Florida became the second, with its law set to take effect July 1, 2025. In April 2025, EPA Administrator Lee Zeldin said the agency would expeditiously review new science on fluoride in drinking water, while Health Secretary Robert F. Kennedy Jr. said he planned to push the CDC to stop recommending fluoridation.

For local officials under pressure to strip fluoride from water systems, the new evidence reset is clear: the level typically added in U.S. communities did not appear to harm cognition, even as the politics around the mineral grew more polarized. The public-health question now is not only whether fluoridation prevents cavities, but whether policy makers are willing to keep one of the nation’s most equitable dental protections in place.