A large new study finds no evidence that fluoridated drinking water affects children’s IQ or decreases cognitive abilities in older adults.
Published April 13 in the Proceedings of the National Academy of Sciences (PNAS), the research reports no difference at any life stage between people who grew up with community water fluoridation and those who did not. “We find no evidence that [community water fluoridation] is negatively associated with adolescent IQ or adult cognitive functioning,” the authors wrote.
The findings contrast with announcements from Health and Human Services Secretary Robert F. Kennedy Jr. directing the CDC to revisit its long-standing recommendation to add fluoride to drinking water, and they differ from some previous studies that suggested links between fluoride and lower IQ. Researchers note those earlier studies were often conducted in countries with much higher fluoride concentrations than those permitted in the United States.
The study was led by Rob Warren, PhD, a sociologist and population health expert at the University of Minnesota. Warren’s team used data from the Wisconsin Longitudinal Study, which has followed more than 10,000 people who graduated high school in Wisconsin in 1957. Participants completed IQ tests at age 16 and underwent cognitive testing at ages 53, 64, 72, and 80.
Because the Wisconsin study was not originally designed to measure fluoride exposure, researchers lacked urine or blood fluoride levels and instead estimated exposure using records of when community water fluoridation began in participants’ areas. Warren previously led a November 2025 study that similarly found no link between early-life community water fluoridation and brain function at age 60.
Expert reactions emphasized that, at the levels used for community water fluoridation in the U.S., there is no evidence of adverse neurodevelopmental or cognitive effects. Scott Tomar, DMD, a spokesperson for the American Dental Association, said the research provides important information amid misinformation and reinforces that fluoridation does not affect IQ or cognition. Danelle Fisher, MD, a pediatrician, called the findings reassuring and said they support the use of fluoride in proper amounts. Graham Tse, MD, a pediatrician and chief medical officer at MemorialCare Miller Children’s & Women’s Hospital, agreed that low levels of fluoride in U.S. drinking water pose no known health threat while noting that very high exposures can cause harm, as with many substances.
History and current policy: Fluoride’s dental benefits were first noted in 1909. In 1945 Grand Rapids, Michigan, became the first U.S. city to add fluoride to municipal water, and studies at the time reported substantial declines in tooth decay among children born after fluoridation began. The U.S. Public Health Service recommended fluoridation in 1962. The CDC states the optimal fluoride level to prevent cavities is 0.7 milligrams per liter (mg/L); the legal limit for fluoride in U.S. drinking water is 4 mg/L.
Today, more than 70% of people on U.S. public water systems receive fluoridated water—over 200 million Americans—but the number of fluoridated communities is declining in some places. Two states, Utah and Florida, have enacted bans on fluoride in drinking water, and other states have pending legislation to limit fluoridation. Since 1995, dozens of individual communities in Wisconsin have stopped fluoridation.
How fluoride works and risks: Fluoride, a naturally occurring chemical found in water and dental products, helps prevent cavities by inhibiting cavity-causing bacteria, strengthening tooth enamel, reversing early decay, and supporting bone formation. Excessive fluoride intake can cause dental fluorosis, which may show as white spots or brown stains on teeth.
Benefits and public health impact: Experts note consistent evidence that water fluoridation reduces tooth decay, lessens the severity of cavities, saves families and communities money on dental care, and reduces missed work or school days due to dental problems. Scott Tomar warned that stopping fluoridation would likely lead to increased tooth decay, with the largest and earliest effects seen among young children.
Oral health and overall health: Dental health affects overall health. Gum disease can affect blood sugar control in people with diabetes and increase risks for heart disease and respiratory infections. Poor dental health may contribute to chronic disease development and can complicate existing conditions such as kidney disease. Cavities can lead to abscesses and infections that spread beyond the mouth.
CDC recommendations for good oral health include avoiding foods and drinks with added sugars, drinking fluoridated water and using fluoridated toothpaste, brushing at least twice a day and flossing regularly, and visiting the dentist at least once a year. Pediatricians advise parents to model regular brushing and flossing, limit sugary drinks and snacks for children, avoid letting babies fall asleep with juice or soda in a bottle, and minimize sticky gummy products. While universal access to high-quality dental care and perfect dental habits might reduce the need for community fluoridation, experts say that is not the current reality—fluoridation remains a cost-effective public health measure to promote dental health.
