Fluoride in drinking water has no negative effect on IQ or cognitive function, study says
Fluoride exposure from drinking water during childhood has no impact on IQ in adolescence or adulthood, a new study published Monday finds.
Researchers from the University of Minnesota, the University of Wisconsin and the University of Michigan looked at community water fluorination levels in Wisconsin in the 1940s and 1950s. They tracked more than 10,000 residents' test scores throughout their school years, as well as results from multiple cognitive tests administered between ages 53 and 80.
The team found no difference in IQ between those exposed to fluoride in drinking water versus those who were not, according to results published in the journal Proceedings of the National Academy of Sciences (PNAS).
The findings come as states, including Florida and Utah, have enacted bans on fluoride in public drinking water.
Rob Warren, study author and professor at the University of Minnesota, told ABC News that he was driven to do the study after hearing claims linking fluoride in drinking water to low IQ and being disappointed by the evidence cited.
Warren's new study follows one published last year in Science Advances that also found no link between fluoride exposure in the United States and reduced cognitive performance.
"The exposures we measure are much more relevant to policy questions than a lot of other research," Warren said. "So what we find is nothing. There's just no relationship in both studies between fluoride exposure, municipal fluoride exposure, you know, through drinking water and cognition."
The study published Monday comes with some caveats. Researchers had to estimate exposure to fluoride based on where participants lived. They were also unable to test urine or blood samples to measure exact levels of fluoride.
Fluoride is a mineral that naturally occurs in water sources such as lakes and rivers, and is even naturally present in some foods and beverages, according to the American Dental Association (ADA). Studies have shown that fluoride is beneficial to teeth: it prevents cavities and repairs damage to teeth caused by bacteria in the mouth, and also makes tooth enamel stronger and rebuilds weakened tooth enamel, the ADA says. It also replaces minerals lost from teeth due to acid breakdown, according to the Centers for Disease Control and Prevention (CDC).
Because of its beneficial effects, fluoride is added to some dental products, such as toothpaste, to help prevent cavities.
The CDC had previously named fluoridation of drinking water as one of the 10 great public health interventions of the 20th century. However, influential skeptics, such as Health and Human Services Secretary Robert F. Kennedy Jr., have raised doubts about the benefits of fluoride.
In an interview with NPR in November 2024, Kennedy reiterated his promise to persuade local governments to remove fluoride from their water supplies. He has claimed that fluoride in drinking water negatively affects children's neurological development and that other countries that have removed fluoride from their water supplies have not seen an increase in cavities.
Last year, Kennedy said he was planning to assemble a task force and ultimately to change the CDC's guidance so that it no longer recommends adding fluoride. At the time, he cited a review that found children who were exposed to fluoride about twice the recommended limit for the U.S. demonstrated lower IQs.
However, some researchers cautioned that much of the underlying data in the review Kennedy cited was pulled from other countries, where fluoride exposure is far higher than levels used in drinking water in the U.S.
Ultimately, the Environmental Protection Agency sets guidance on the maximum level of fluoride in U.S. drinking water.
Many doctors and dental associations argue that fluoride in water is still a crucial, low-risk/high-reward public health tool, especially for children and adults who may not be able to practice regular dental hygiene.
The association calls community water fluoridation "the single most effective public health measure to prevent tooth decay."
"Studies prove water fluoridation continues to be effective in reducing dental decay by at least 25% in children and adults, even in the era of widespread availability of fluoride from other sources, such as fluoride toothpaste," the ADA states on its website. "So, by simply drinking fluoridated water, you are doing something good for your oral health."
Warren said he hopes the research will help inform policy in other states considering bans on fluoride in drinking water.
"Whether that's county commissioners or city managers or whoever is in charge, and they're all asking a similar question is, 'How do the benefits compare to the risks?''" Warren said. "And I want them, I hope, to do that in light of the best possible evidence about all the benefits and all the risks, and hopefully this [study] makes a real contribution to that."
ABC News' Sony Salzman and Dr. Grace Hagan contributed to this report.
