For several years, fluoride in drinking water has sowed doubt among many American parents. Many cities incorporate fluoride into their drinking water – a method known as fluoridation – to promote oral health. However, in recent years, some have argued that consuming fluoride could have a negative impact on children’s IQ, to the point that American states such as Utah and Florida have stopped the practice. Across the Atlantic, the debate has taken on a national scale.
Fluoride in drinking water and children’s IQ: what the American study shows
To find out whether these fears may apply to the low doses used to protect teeth, researchers at the University of Minnesota analyzed decades of archival data on when water fluoridation began in Wisconsin cities. Their work, published in 2026 in the journal PNASis based on the Wisconsin Longitudinal Studywhich has followed 10,317 American high school students since 1957 and measured their IQ and then their cognitive abilities up to the age of 80.
To assess exposure to fluoridethe researchers used the archives of Wisconsin towns: start date of fluoridation, natural presence of fluoride in wells, size of towns. They classify each student according to the age at which they were exposed, then cross-reference this information with IQ tests taken at age 16 and batteries of memory and language tests at ages 53, 64, 72 and 80.
Results: Whether tap water was fluoridated or not, the authors found no difference in IQ at age 16 or any particular cognitive decline later in life. For co-author Gina Rumore, this data “provide no support for the claim that fluoridation of drinking water has a detrimental effect on the IQ of children or the cognitive abilities of adults..
A study of 10,317 high school students, tests from 16 to 80 years old
“Utah, Florida and many municipalities have chosen to remove fluoride from drinking water based on flawed studies that examined the effects of exposure to high doses of fluoride on IQ.”said John Robert Warren, professor in the Faculty of Arts and Humanities and lead author of the study. “Because the levels of fluoride added to drinking water in the United States are much lower, almost all of the data from these earlier international studies are irrelevant to U.S. public policy debates.”.
Seen from the outside, the protocol is impressive. Researcher Bruce Lanphear, professor of health sciences at Simon Fraser University in Canada who himself published a study in 2019 finding a slight link between fluoride and IQ in young children, speaks in NBC News about “one of the most rigorous attempts to examine fluoridation and cognition across the lifespan“. He points out, however, that the study did not directly measure fluoride in blood or urine, which leaves a small margin of uncertainty.
Parents, fluoride and tap water: how to interpret these results
For families, this work brings a reassuring message: at the levels used to prevent cavities, adding fluoride to tap water did not lower the Children’s IQ followed, nor altered their long-term memory. In France, distribution water is not fluoridated,
In France, the fluoridation water has not been practiced since the end of the 1980s. On the other hand, salt fluoridation has been practiced since 1985. The presence of fluoride in tap water is therefore of natural origin. Exposure comes mainly from toothpastes and some mineral waters.