Fluoride in U.S. drinking water does not reduce IQ, a new study finds Skip to content Subscribe today Every print subscription comes with full digital access Subscribe Now Menu All Topics Health Humans Anthropology Health & Medicine Archaeology Psychology View All Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes View All Earth Agriculture Climate Oceans Environment View All Physics Materials Science Quantum Physics Particle Physics View All Space Astronomy Planetary Science Cosmology View All Magazine Menu All Stories Multimedia Reviews Puzzles Collections Educator Portal Century of Science Unsung characters Coronavirus Outbreak Newsletters Investors Lab About SN Explores Our Store SIGN IN Donate Home INDEPENDENT JOURNALISM SINCE 1921 SIGN IN Search Open search Close search Home INDEPENDENT JOURNALISM SINCE 1921 All Topics Earth Agriculture Climate Oceans Environment Humans Anthropology Health & Medicine Archaeology Psychology Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes Physics Materials Science Quantum Physics Particle Physics Space Astronomy Planetary Science Cosmology Tech Computing Artificial Intelligence Chemistry Math Science & Society All Topics Health Humans Humans Anthropology Health & Medicine Archaeology Psychology Recent posts in Humans Health & Medicine New mutations help the H5N1 bird flu virus infect cows but not people By Tina Hesman Saey11 minutes ago Health & Medicine Fluoride in U.S. drinking water does not reduce IQ, a new study finds By Elie Dolgin21 hours ago Life Talking dogs and chatty cats could one day ‘speak’ in our language By Laura Sanders24 hours ago Life Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes Recent posts in Life Health & Medicine New mutations help the H5N1 bird flu virus infect cows but not people By Tina Hesman Saey11 minutes ago Life Smithsonian secrets most likely to blow your mind By Meghan Rosen and Stephen Voss2 hours ago Life Talking dogs and chatty cats could one day ‘speak’ in our language By Laura Sanders24 hours ago Earth Earth Agriculture Climate Oceans Environment Recent posts in Earth Animals For gray whales, San Francisco Bay is becoming a deadly pit stop By Gennaro TommaApril 13, 2026 Climate Emperor penguins are marching toward extinction. 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But it’s also become a contentious political issue. Tara Moore/Stone/Getty Images By Elie Dolgin 21 hours ago Share this:Share Share via email (Opens in new window) Email Share on Facebook (Opens in new window) Facebook Share on Reddit (Opens in new window) Reddit Share on X (Opens in new window) X Print (Opens in new window) Print Two U.S. states and more than a dozen cities and counties have moved in the past year to stop adding fluoride to community drinking water, citing research suggesting the mineral could harm children’s brain development. But a new analysis of cognitive outcomes tracked over decades finds no evidence that water fluoridation is associated with lower adolescent IQ or diminished mental abilities later in life, researchers report April 13 in the Proceedings of the National Academy of Sciences. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday. The results, based on standardized intelligence testing of more than 10,000 people in Wisconsin followed since their senior year of high school in 1957, challenge the idea that typical fluoridation levels in public drinking water pose a neurodevelopmental risk, a central point of contention in ongoing policy debates. “It’s very strong data,” says Steven Levy, a dentist and public health researcher at the University of Iowa in Iowa City who was not involved in the research. “There’s no strong signal at all coming through that should give us concern.” However, given the politically charged nature of water fluoridation and continued differences in how researchers interpret the available evidence, the findings are unlikely to be the last word on the issue. Fluoride has been added to public water supplies in North America since the 1940s, after studies of communities in the western United States showed that naturally occurring fluoride in groundwater strengthened tooth enamel and reduced cavities. The practice became one of the most widespread public health interventions of the 20th century and is widely credited with sharply lowering rates of tooth decay in children. But beginning around the turn of the century, concerns about possible neurological effects began to surface, fueled largely by studies of children exposed to unusually high levels of naturally occurring fluoride in groundwater in parts of China, India and elsewhere. Those concerns came to a head last year when researchers affiliated with the U.S. government’s National Toxicology Program synthesized epidemiological evidence and reported a link between elevated fluoride exposure and lower IQ scores in children — with the strongest associations observed at fluoride concentrations above the World Health Organization’s guideline of 1.5 milligrams per liter, and mixed results below that threshold. That study drew widespread attention, including from a U.S. federal district court, which cited the finding in ordering the Environmental Protection Agency to review fluoride’s potential neurotoxic effects. Federal health officials also referenced the research when announcing plans to reassess the safety and benefit of ingestible fluoride supplements and to reevaluate public water fluoridation policies. But many scientists were less convinced. As critics were quick to point out, much of the underlying evidence drew from populations exposed to substantially higher fluoride concentrations than
Fluoride in U.S. drinking water does not reduce IQ, a new study finds
