New, ‘Rigorous’ Study Offers Answer on Whether Fluoride in Drinking Water Affects Kids’ IQs

A new study of thousands of people in the U.S. has found no link between fluoride in water at the levels typically used in the U.S. and adolescent IQ or cognition as an adult. The research builds on another study from last year by the same lead author with a similar conclusion but did not include information on IQ.

Fluoride in community water has become a hotly debated topic, with critics claiming that it can have harmful health effects in kids, especially on cognitive development. Two states, Florida and Utah, have banned Florida in drinking water, and at least 20 more have introduced bills to do the same, NBC News reported.

However, most of the research that’s found a link between fluoride exposure and lowered IQ includes participants who were exposed to “massive doses,” Robert Warren, Ph.D., professor of sociology specializing in public health at the University of Minnesota and lead author of the new study, tells TODAY.com.

“Nobody’s talking about putting massive, toxic doses in the public drinking water,” he adds. “Reviews of the evidence where we’re comparing recommended doses to (no fluoride in water) tend to find that there’s no relationship.”

Warren’s recent study, published April 13 in the Proceedings of the National Academy of Sciences, looked at 10,317 individuals who graduated from high school in Wisconsin in 1957. Researchers estimated their fluoride exposure up to age 14 based on where they lived, gathered adolescent IQs based on tests given in high school, and measured adult cognition at four different points using age-appropriate, standardized tests.

“The analysis indicated that participants who were exposed to community water fluoridation as adolescents did not perform significantly worse or better than peers who were never exposed to fluoridated water as adolescents — at any of the ages at which IQ or cognition was assessed,” a press release explained.

Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada who’s previously researched fluoride and IQ, told NBC News the new study is “one of the more rigorous attempts to examine fluoridation and cognition across the life course.”

What sets Warren’s study (and his earlier one) apart from previous research is that they look at the long-term effect of fluoride exposure in childhood, Warren explains.

“If the claim is true that (fluoride in water) affects IQ, then it really ought to affect long-term cognition, as well,” he says. “And again, there’s no relationship. There’s just nothing, no connection between IQ or cognition in the short- or the long-term and fluoride exposure in childhood.”

It’s challenging to study the health outcomes of fluoride exposure via community water because you need to have a representative group of participants (so you can apply the conclusions to a more general population), data on IQs and what participants were exposed to, and you have to follow them over time, Warren says. But there just aren’t that many groups where all this data is available.

Warren even cautions that his study includes mostly white participants because it looks at Wisconsin high school graduates. Lanphear adds that a weakness in the new study is that it estimates fluoride exposure based on where participants lived, rather than measuring exactly how much they consumed.

Warren says he’d like to see more research on the topic, especially a study that could follow participants from birth.

For now, Warren says it’s well-established that there are benefits to community water fluoridation, like reducing rates of cavities by about 25%, according to the U.S. Centers for Disease Control and Prevention. The question is whether they outweigh any potential risks — and “the No. 1 (risk) people point to is IQ, and I think our evidence has cast out on that,” Warren says.

For parents concerned about kids’ fluoride exposure, Warren advises not to let children swallow toothpaste, and “don’t worry about the water.”

“The risks don’t seem to be there for cognition or IQ. … I have kids, I have no concerns about them drinking the water,” he says.