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Responses to fluoride study flood in from all over the globe

August 27, 2019

By David Burger and Jennifer Garvin

 image of fluoridation icon
Alongside organizations and publications around the world, the ADA on Aug. 19 issued a press statement in response to widespread media interest in a study that suggested an association between higher prenatal fluoride exposure and lower IQ scores in children 3-4 years of age.

“The American Dental Association remains committed to fluoridation of public water supplies as the single most effective public health measure to help prevent tooth decay,” according to the ADA statement. The Association also noted that this commitment is shared by the World Health Organization, U.S. Public Health Service, Centers for Disease Control and Prevention, American Medical Association and American Academy of Pediatrics.

One of the study’s authors, Dr. Angeles Martinez-Mier, chair of cariology, operative dentistry and dental public health at the Indiana University School of Dentistry, said while she stands “fully behind our study’s conclusions, as an individual, I am happy to go on the record to say that I continue to support water fluoridation.” Dr. Martinez-Mier is a member of the ADA Council on Advocacy for Access and Prevention’s National Fluoridation Advisory Committee.

Study prompts quick response

For the study, researchers examined whether there was any association between IQ of children and fluoride exposure of their mothers during pregnancy. The study measured the maternal urinary fluoride levels in 512 women across 10 Canadian cities during each trimester of their pregnancies as well as the self-reported fluoride intake from 400 women. The study also recruited a subset of 601 children — 254 who lived in a nonfluoridated region, 180 who lived in a fluoridated region and 167 whose fluoridation status was unknown — and completed neurodevelopmental testing. The results showed that a 1 milligram per liter increase in maternal urinary fluoride was associated with a statistically significant 4.49-point lower IQ score in boys and a non-significant increase of 2.4 IQ points for girls. The researchers concluded that “maternal exposure to higher levels of fluoride during pregnancy was associated with lower IQ in children age 3-4.”

Christine Till, Ph.D., an assistant psychology professor at Toronto’s York University and co-author of the study, defended the study in an interview with ADA News from the Netherlands. She anticipated the controversy of the research, given that there are strong opinions on both sides of the issue, she said.

“We’ve been under so much scrutiny,” Dr. Till said of the review process. “We’ve addressed dozens and dozens of reviews.”

“This decision to publish this article was not easy,” wrote the publishing journal’s editor, Dimitri A. Christakis, M.D., in an editorial comment accompanying the study. “Given the nature of the findings and their potential implications, we subjected it to additional scrutiny for its methods and the presentation of its findings. The mission of the journal is to ensure that child health is optimized by bringing the best available evidence to the fore. Publishing it serves as testament to the fact that JAMA Pediatrics is committed to disseminating the best science based entirely on the rigor of the methods and the soundness of the hypotheses tested, regardless of how contentious the results may be. That said, scientific inquiry is an iterative process. It is rare that a single study provides definitive evidence. This study is neither the first, nor will it be the last, to test the association between prenatal fluoride exposure and cognitive development. We hope that purveyors and consumers of these findings are mindful of that as the implications of this study are debated in the public arena.”

In responding to the study’s conclusion, the ADA said that “public health policy is based on a collective weight of scientific evidence” and called for “further scientific study of the issue to see if the [study’s] findings can be replicated with methods that demonstrate more conclusive evidence.”

In a statement published online Aug. 19 in the American Academy of Pediatrics News, the academy said it will also continue to recommend children use age-appropriate amounts of fluoride toothpaste and drink fluoridated tap water.

“There are thousands of articles pointing to the safety of community water fluoridation and we need to continue to look at the impacts, but this study doesn’t change the benefits of optimally fluoridated water and exposure to fluoride,” said Patricia A. Braun, M.D., professor of pediatrics at the University of Colorado and chair of the AAP Section on Oral Health Executive Committee.

Dr. Braun and Aparna Bole, M.D., chair of the AAP Council on Environmental Health Executive Committee, said “the results of the study are difficult to interpret given that the IQ difference was small and in one group it only appeared in boys. In the group where an association was seen for boys and girls, the fluoride intake was self-reported, which is less reliable.” The two experts also stressed the study did not look at children’s fluoride intake, only that of pregnant women.

American experts weigh in

Other organizations questioned the study’s credibility, methodology and conclusions.

The American Council on Science and Heath published a story a few days after the study was released called “No, Fluoride Doesn’t Lower IQ. It Fails to Satisfy Hill’s Criteria of Causality.” Alex Berezow, Ph.D., vice president of scientific affairs for the council, wrote that the study’s conclusions are “doubtful” and that the study doesn’t meet the benchmarks devised by epidemiologist Austin Bradford Hill that are meant to “tease apart correlation from causation.”

Dr. Berezow said that the paper is not consistent with other data on the topic, so that particular benchmark is not reached. “While it is true that extremely high doses of fluoride harm the brain, people are not exposed to those levels by drinking water,” he wrote.

He continued by opining that the study doesn’t meet the benchmark for coherence, noting that “while the authors conclude that a 1-mg increase in fluoride detected in the mother’s urine is linked to an IQ drop of about 4.5 points in boys, there is no statistically significant IQ difference among girls … Obviously, that is incoherent. There is no sensible biochemical reason why fluoride would harm the brains of boys but not those of girls.”

Dr. Berezow concludes with this assessment: “So, are the authors wrong? Probably.”

Another story, published on Forbes.com and written by senior contributor Bruce Y. Lee, M.D., weighs in on the subject, again asserting that the study is invalid.  

An associate professor of international health at the John Hopkins Bloomberg School of Public Heath, Dr. Lee says in his piece, “If you think these findings prove that fluoride in drinking water leads to lower intelligence, remember that associations do not mean that one thing causes another … Observational studies, like this JAMA Pediatrics one, cannot, cannot, cannot, cannot prove cause and effect. People who live in areas where tap water is fluoridated could also be exposed to other things or have behaviors that may affect their children’s IQ scores. For example, could they or their children be eating more processed foods with artificial ingredients? Could they be exposed to more chemicals in the environment? We do not know enough about the details of the study participants’ lives to know what really is happening.”

Furthermore, Dr. Lee believes that “IQ scores are just one measure of thinking ability and development and an imperfect one at that. IQ scores can be misleading as not everyone can perform to the best of their ability on tests.”

Dr. Lee notes that the ADA has been consistent by emphasizing the more than 70 years of scientific research conducted, with the overwhelming evidence showing that fluoride is safe and effective in preventing tooth decay.

Steven Novella, M.D., a clinical neurologist at Yale’s School of Medicine, questioned in an Aug. 21 article on the web site Science-Based Medicine how the study’s authors interpreted the study’s data and pointed out what he called several “red flags” in the study, including “the huge variance in results, and the disconnect between performance and verbal IQ.” He added, “The study is at odds with large body of evidence showing no association with normal fluoride exposure and IQ. There are other criticisms along these same themes. There are a lot of anomalies in the statistics, meaning that you could choose to look at the data in different ways and get different results.”

The American Fluoridation Society issued a statement Aug. 23 that disputed the study’s conclusions. “The American Fluoridation Society welcomes robust research on fluoride and fluoridation,” the statement read. “However, we are concerned that the [study] may produce headlines that do not accurately reflect the study’s data and methodology. It should be understood that an ‘association’ does not prove causation.”

The statement continued: “It’s important to consider the context. In recent years, multiple studies have found no link between fluoride exposure and intelligence/cognitive skills … People and communities should not be scared into making a decision that will harm their oral health and overall health.”

The American Association for Dental Research too weighed in on the study, releasing a statement on Aug. 20 that said that while the study results raise “important questions worthy of future research, the authors identify a number of limitations that make it unclear if and how these results should influence current policy on water fluoridation. One of the study’s most significant limitations is the quantification of fluoride intake. Only beverages were considered in the measure of fluoride intake, but there are several common dietary sources of fluoride. Furthermore, data on beverage intake were collected using self-report, which is subject to recall bias, and the authors did not have access to the concentration of fluoride from each subject’s tap but had to estimate based on where the subject lived. As the authors state, an individual’s tap water could be supplied by multiple treatment plants.”

Worldwide questions

Opinions across the world have been equally skeptical of the new study.

The Science Media Centre, an independent British organization that sources expert opinions on science in the news, compiled expert opinion on the study this week, providing statements from eight professors and scientists across the world that all call into question the legitimacy of the study’s findings.

Thom Baguley, Ph.D., professor of experimental psychology at Nottinghall Trent University in England, said, “The claim that maternal fluoride exposure is associated with a decrease in IQ of children is false … In summary, it is not correct to imply that the data here show evidence of a link between maternal fluoride exposure and IQ. The average change in IQ is not statistically significant.”

Dr. Oliver Jones, associate professor of analytical chemistry at RMIT University in Australia, said that “there is also a lot of variation in the data — which makes drawing firm conclusions/predictions from it difficult. There are also a number of potential confounding factors, including the fact that the water intake was self-reported and, as the authors admit, some of the methods used are not validated.”

Alastair Hay, Ph.D.,  professor emeritus of environmental toxicology at the University of Leeds in England, said the study contains a “crucial failure” when the authors acknowledge that the maternal intake of fluoride had not been validated. “For a substance with a short half-life, such as fluoride, urine concentrations vary hugely and are really only representative of the last drink. Validation of intake is something you just do before looking at associations.” He adds that another “major serious gap” is the “range of exposure to multifarious substances, including lead, that the children would have had between birth and IQ assessment at ages 3 and 4. We know that lead exposure has devastating effects on IQ in children and this study takes no account of postnatal lead exposure.”

Stuart Ritchie, Ph.D., a lecturer at King’s College London, summed up his misgivings about the study by saying, “I wouldn’t have much confidence in this finding being robust or replicable.”

Media response

Media coverage of the study has been extensive, with stories appearing in Time magazine, The Washington Post, the Philadelphia Inquirer and many more.

The Inquirer quotes Dr. Brittany Seymour, a Harvard School of Dental Medicine assistant professor and member of the ADA CAAP’s National Fluoridation Advisory Committee. In the story, she said one study is not enough to alter public health policy, especially such a well-researched one. “I’m passionate about teeth, but my most important job is as a mom. I’m raising my daughter in Boston," she said of her 6-year-old in the story. "Boston is fluoridated. I haven’t once felt concern that she’s drinking fluoridated water. In fact, I would be much more concerned if she wasn’t. This study doesn’t change my comfort level with my own daughter continuing to drink fluoridated water.” She was also quoted in USA Today and The Washington Post.

Dr. Till appeared on Canada’s CTV News to defend the study. “There’s been a bit of pushback as you can imagine, when you’re doing such a controversial study,” she said on the program. “The data are what the data are … Our recommendation is that pregnant women reduce fluoride intake in pregnancy. This is a reasonable conclusion based on the findings and not just our findings.”

In the ADA News interview, Dr. Till addressed whether more studies will be forthcoming about the safety and necessity of fluoride. “I should hope so,” she said.

The ADA policy statement on fluoridation states that the association “unreservedly endorses the fluoridation of community water supplies as safe, effective and necessary in preventing tooth decay. This support has been the Association's position since policy was first adopted in 1950.”

According to the ADA press statement, “The ADA remains focused on how and if emerging evidence might impact public health recommendations and policies. We will continue to evaluate the validity of emerging evidence and research to support the advancement of the health of the public.”

More information about fluoride and community water fluoridation can be found at ADA.org/fluoride.