University of Minnesota research counters claims that fluoride in water lowers IQs

Jeremy Olson, The Minnesota Star Tribune on Apr 14, 2026

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MINNEAPOLIS – A new study by University of Minnesota researchers found no evidence to support fears that childhood consumption of fluoride and fluoridated water reduces intelligence.

Utah and Florida in 2025 banned the use of fluoride in public water supplies, despite its well-documented benefits for oral health, after a report showed an association between childhood consumption of the mineral and performance on cognitive tests.

The U results suggest that these states were at best hasty, because the association was based on consumption of very high levels of fluoride in China and developing countries.

“Almost all prior evidence from those international studies is not relevant to U.S. public policy debates,” said John Robert Warren, the U sociologist who led the latest study.

The majority of U.S. cities add fluoride to their water supplies to reduce tooth decay. The Centers for Disease Control and Prevention once called this one of the greatest public health achievements of the past century, because it provides low-cost dental benefits to everyone regardless of income or demographics.

But concerns have persisted, both among highly conservative Americans who oppose the government public health measure and among highly liberal Americans who oppose additives to their diets.

Those concerns gained a boost last year when President Donald Trump appointed Robert F. Kennedy Jr. as the nation’s health secretary. Kennedy has likened fluoride to “industrial waste” and suggested that communities should stop adding it to drinking water.

Fluoride is a naturally occurring element, but some added to drinking water is captured as a byproduct of commercial fertilizer production and mining.

To examine the question of whether the fluoride is causing harm, the U researchers looked at cognitive performance of about 10,000 Wisconsinites whose health and well-being were routinely monitored after they graduated high school in 1957.

The data from the Wisconsin Longitudinal Study allowed researchers to identify if people lived in communities with fluoridated water, at a time when many communities hadn’t added it yet. People in the study also were children before fluoridated toothpaste was commercially available, meaning that drinking water was their primary source of fluoride.

The result: People who grew up in Wisconsin towns with fluoridated water supplies neither performed worse on childhood standardized tests nor developed more cognitive declines as they aged. The findings were published Monday in PNAS, a peer-reviewed scientific journal, and supported with a mix of federal and private grants.

Co-author Gina Rumore said she is a “fairly hippy-dippy parent” who was open to whatever finding the research made about fluoridated water and was eager to inform the debate with U.S. data.

The results “provide no support for the claim that community water fluoridation has any harmful effect on children’s IQ or on adult cognition,” said Rumore, co-director of the U’s Demography and Economics of Aging Coordinating Center.

The question of its efficacy has significance for Minnesota, which mandates that 731 municipalities add fluoride to their public water supplies if they don’t have elevated, natural levels already.

Minnesota has one of the highest rates in the nation of people whose drinking water contains natural or supplemental fluoride. The state also ranked top five for IQ scores in one recent comparison and above average for dental health.

The U study did find slightly higher IQ levels among people who were not exposed to fluoridated water until they were adolescents, either because they moved or their communities added it after they were born. However, that finding was not statistically significant and was confounded by the fact that these people came from wealthier households and communities who tend to do better on tests, Rumore said.

Warren published a similar study last year using a larger dataset of Americans who were in high school in 1980, but it was limited because it only identified where they went to school and not if they lived in communities with fluoridated water. The results actually showed better academic achievement among students who were likely consuming fluoridated water, at least confounding the theory that it hurt cognition.

The CDC currently recommends a concentration of 0.7 milligrams per liter of fluoride in public water supplies. The federal agency lowered that amount in 2015 from 1.2 after determining that many people were getting fluoride exposure through toothpaste and other sources.

Consuming too much fluoride can result in dental fluorosis, or a mottling or discoloration of teeth.

Both the current and former CDC recommendations are below the fluoride levels in the 2025 report by researchers at the National Institute of Environmental Health Sciences that showed an association between fluoride consumption and lower IQs. The results were found among children in China, India and other countries where naturally occurring fluoride levels can far exceed U.S. levels.