WISCONSIN — A study published April 13, 2026, in the Proceedings of the National Academy of Sciences found no differences in cognitive outcomes between Wisconsin residents who grew up with community water fluoridation and those who did not, at any stage of life through age 80. The study is the first to measure community water fluoridation exposure during childhood in the United States and its potential impact on cognition up to that age.

Rob Warren, a sociologist and population health expert at the University of Minnesota, conducted the research. "I was curious about the short-term effects on adolescent cognition, but also cognitive functioning later in life," Warren said. The study used data from the Wisconsin Longitudinal Study, which has followed 10,317 Wisconsin residents since they graduated from high school in 1957. Participants took IQ tests at age 16 and cognitive tests at ages 53, 64, 72 and 80.

The research team estimated participants' fluoride exposure based on records of when community water fluoridation began in their areas and the locations of untreated wells. The team did not have participants' urine or blood test data to measure fluoride exposure because the Wisconsin Longitudinal Study was not designed to assess fluoride levels.

The findings come as debate over water fluoridation has grown across the country. Health Secretary Robert F. Kennedy Jr. has said, "Fluoride is 'industrial waste' associated with IQ loss." Two states, Utah and Florida, have enacted bans on adding fluoride to drinking water, and Kentucky, Louisiana, Missouri and Oklahoma have pending legislation to prohibit water fluoridation. Since 1995, 86 Wisconsin communities have stopped adding fluoride to municipal water systems, according to the state's Department of Natural Resources.

Small studies conducted in China and other countries with fluoride concentrations higher than the U.S. legal limit had suggested a possible link between fluoride exposure and children's IQ. The legal limit for fluoride in U.S. drinking water is four milligrams per liter. The Centers for Disease Control and Prevention recommends an optimal fluoride level of 0.7 milligrams per liter in drinking water to prevent cavities.

"I think that the public can be assured. There is no association with community water fluoridation and any measure of IQ or neurodevelopment," said Dr. Scott Tomar, head of the department of population oral health at the University of Illinois in Chicago.