New scientific paper exposes serious flaws in fluoride-IQ studies

Newswise — WASHINGTON, March 25, 2024 /PRNewswire/ -- Hundreds of millions of people around the world receive significant dental health benefits because their tap water is adjusted to the recommended amount of fluoride. Yet opponents of water fluoridation often cite a 2019 Canadian study (Green et al.) to claim that fluoride affects children's IQ scores. This claim has been refuted by a new peer-reviewed analysis. This published analysis shows that the Canadian researchers relied on data that cannot report fluoride measurement and does not accurately measure IQ.

The authors of this analysis wrote that studies relying on these data to make claims about fluoride and IQ "should be considered unacceptable for legal and policy purposes." The new analysis was just published by the Journal of Community Dentistry & Oral Epidemiology.

The Green authors and other researchers claimed an association between fluoride exposure and IQ by examining data from the Maternal-Infant Research on Environmental Chemicals (MIREC) database. When the researchers compared the average IQ score between fluoridated and non-fluoridated cities in Canada, the scores were virtually identical. Curiously, the researchers did not highlight that point. Instead, the Green researchers reported a fluoride-IQ association after they estimated fluoride levels of the pregnant women using spot urine samples collected during pregnancy.

However, the new analysis reminds readers that spot samples of urinary fluoride cannot accurately measure a person's exposure to fluoride, let alone that of a fetus. Moreover, the measurement of their children's IQs was unreliable, for example, because there were different IQ test administrators in each city. The authors of this analysis conclude:

"Because the MIREC database offers neither valid data on maternal or fetal fluoride exposure, nor reliable measures of the IQ of the resulting children, the database cannot be used to make claims that fluoride exposure affects IQ." 

"This analysis is huge. It means that seven Canadian studies that stand on the MIREC database have come tumbling down like a house of cards," said Dr. Johnny Johnson, President of the American Fluoridation Society. "It's important that we hold all research to high standards."

The lead author of the analysis was Juliet Guichon, a professor in the University of Calgary Cumming School of Medicine. The analytical team included Andrew Rugg-Gunn and Colin Cooper. Rugg-Gunn is a British scientist and international expert in the measurement of fluoride intake. Cooper is a British psychologist who has authored more than a dozen books, chapters or scientific articles about human intelligence and related topics. The fourth co-author was James Dickinson, an epidemiologist and professor of Family Medicine in the University of Calgary Cumming School of Medicine.

A lot is at stake. Tooth decay (cavities) is the most common chronic disease for children and adults. The Centers for Disease Control and Prevention reports that drinking fluoridated water reduces tooth decay by 25% for adults and children. Water fluoridation is endorsed by the American Academy of Pediatrics, American Dental Association, and other leading health, medical and dental organizations.

Policy makers and health professionals should recognize that the quality of fluoride-IQ studies varies widely. In fact, a 2023 systematic review examined 30 fluoride-IQ studies and found that 29 studies were at moderate to high risk of bias (lower quality). The only study at low risk of bias (highest quality) found no link between fluoride and IQ scores. In addition, a recent meta-analysis of studies reported that "fluoride exposure relevant to community water fluoridation is not associated with lower IQ scores in children."

In some cases, the flaws of a study are not recognized until many months or even years after it was published. It's important for journals to follow the lead of BMC Public Health, which retracted a fluoride-IQ study after it learned of serious concerns about the study's methodology.

Given the concerns identified in this new analysis, as well as concerns raised by numerous experts, we urge JAMA Pediatrics to consider retracting the Green et al. paper. It should be noted that the journal has retracted papers when similar concerns were raised after their publication. 

Only one fluoride-IQ study has followed individuals over a 30-year period, testing their IQs at multiple ages to assess whether a link existed. Unlike the Canadian studies, this New Zealand study did not rely on spot urine samples. The New Zealand study found no association between fluoride and IQ scores. Data from Australia, Denmark, Spain and Sweden also have revealed no link between fluoride and cognitive deficits.

For more information on the scientific evidence related to fluoride and fluoridation, please visit the American Fluoridation Society at AmericanFluoridationSociety.org.