A large, decades-long study has found no evidence that fluoride in drinking water harms children's intelligence or reduces cognitive function in older adults, directly contradicting claims that have gained traction in recent political debates over water fluoridation.
The research, published April 13 in the Proceedings of the National Academy of Sciences, found no measurable difference at any stage of life between people who grew up with fluoridated water and those who did not. "We find no evidence that community water fluoridation is negatively associated with adolescent IQ or adult cognitive functioning," the study authors wrote.
The study was led by Rob Warren, a sociologist and population health expert at the University of Minnesota. Warren drew on data from the Wisconsin Longitudinal Study, an unusually long-running project that has followed more than 10,000 people since they graduated from high school in 1957. Participants took IQ tests at age 16 and then underwent cognitive testing at ages 53, 64, 72, and 80, giving researchers a rare window into how cognition changes across a lifetime and whether fluoride exposure plays any role in that trajectory.
Because the Wisconsin study was not originally designed around fluoride, researchers did not have blood or urine data measuring exact fluoride levels in participants. Warren's team instead estimated exposure using historical records of when community water fluoridation began in specific areas. That limitation is worth noting, though the study's scale and timespan are significant strengths.
The findings arrive at a politically charged moment. HHS Secretary Robert F. Kennedy Jr. announced in April that he would require the CDC to revise its long-standing guidance on water fluoridation. The new study's conclusions run counter to that push.
Scott Tomar, a spokesperson for the American Dental Association and a professor at the University of Illinois Chicago College of Dentistry, said the research matters precisely because of the current climate. "Despite misinformation that is out there, the best available evidence indicates that community water fluoridation has no effect on IQ, cognition, or other measures of neurodevelopment," Tomar said. He was not involved in the study.
Dr. Danelle Fisher, a pediatrician at Providence Saint John's Health Center in Santa Monica, California, said the findings confirm what previous research has shown. "They reassure us that the use of fluoride in proper amounts does not have any definitive effects on IQ," she told Healthline. "It makes a good case for having fluoride in our drinking water."
This study is the second recent large-scale effort by Warren on the question. A November 2025 study he led also found no link between early-life fluoride exposure and brain function at age 60. Taken together, the two papers represent some of the most comprehensive longitudinal evidence to date on a debate that has persisted for decades.
Fluoride has been added to public water supplies in the United States since the 1940s, with the goal of reducing tooth decay. Experts consistently note that dental health has direct connections to broader physical health, making the stakes of the fluoridation debate larger than they might initially appear.
