Fluoride & IQ: Until recently, concerns were rarely raised
Thanks to fluoride in water, America has been preventing tooth decay for over 75 years. Fluoridation is effective, safe and benefits everyone regardless of age or income. About 3 out of 4 people in U.S. communities enjoy fluoridated 
water. Until recently, concerns about fluoride and IQ were rare.
Opponents of fluoridation began focusing on IQ when a review of studies was published in 2012. They claimed that it showed that lower IQ scores in children were “caused” by fluoride. Here’s why the evidence does not support the claim.
- A review is not an experiment. It does not test cause and effect. The authors looked at 27 dissimilar studies from China, Mongolia and Iran and reported what was observed.
- The authors warned that the studies they reviewed “had deficiencies, in some cases rather serious, which limit the conclusions that can be drawn.” They cautioned that more research would be needed to rule out other factors affecting test scores. This can include nutrition, the quality of schools, and exposure to contaminants such as lead.
- The studies did not describe the water that American children drink. The fluoride in these countries was in some cases more than 5 times what is used for water fluoridation in the United States.
On the contrary. Studies from New Zealand and Sweden have shown that the IQ scores of teens and adults living in fluoridated communities during infancy and childhood were no different than the scores of people who lived in communities without fluoridated water. These two studies are unique because they followed participants over time and tracked IQs and other possible effects, well into adulthood. As a result, these studies are far more accurate.
The Research Focus Shifts
In recent years, opponents have focused on prenatal exposure to fluoride, with studies from Mexico City and Canada, where fluoride exposure is similar to the U.S. and Canada. These studies reported some differences in the IQ scores of 3 and 4 year olds related to the level of fluoride their mothers were exposed to, using maternal urinary fluoride (MUF) spot samples. However, the Canadian study only showed a significant difference for boys — and only on one of the two tests.
Many criticisms have been raised about the quality of these studies including that the results have not been confirmed by other research teams. Such confirmation is standard practice to test the validity of research methods and results.
The Canadian studies were based on only one data set. Those data were collected in a larger study not originally intended to determine if a mother’s exposure to fluoride might affect their children’s IQ. A recent analysis cites authoritative sources that dismiss the validity of both the measure of the individual mothers’ exposures to fluoride and how the IQs of their children were tested.
Any study of IQ differences must take into account the many factors that can affect intelligence scores. Some of these include breastfeeding, nutrition, and mothers’ IQ. When researchers account for these factors, we can have more confidence that the study’s results are not skewed or otherwise affected.
The studies from Mexico City and Canada accounted for some but not all these factors. They relied on IQ testing that was conducted at only one age. By contrast, the New Zealand study tested IQ several times, starting at age 7 and ending at age 38. The fact that multiple test scores were collected, and over a long period time (31 years), means that we can have more confidence in these results over others.
The National Academies Weighs In
In 2015, the National Toxicology Program (NTP) initiated a large review of studies on fluoride and possible cognitive effects. This review included the studies from Mexico City and Canada. Since then, the NTP has produced several drafts of a report on their findings. As is customary, the NTP sought peer-review of its work, choosing the National Academies of Sciences, Engineering and Medicine. After reviewing, the National Academies concluded that the NTP had not identified “clear and convincing” evidence to support its claim that fluoride “causes” low IQ.
Going one step further, the National Academies instructed NTP to clarify several important points. For example, the studies it reviewed do not address or raise safety concerns about low fluoride exposures, “including those typically associated with drinking-water fluoridation.” Because of this. the NTP removed the classification of fluoride as a “hazard”. The revised draft also presented an opportunity to include research, some contradictory, published through November 2021.
The third draft, entitled NTP Monograph on the State of Science, was never resubmitted to the National Academies. Instead it was given to the NTP’s own Board of Scientific Counselors (BSC). They assessed the adequacy of NTP’s responses to the comments it received from the experts who reviewed it. The BSC recommended an additional 93 revisions to the monograph due to 1) scientific issues, 2) insufficient information, 3) imprecise text, and 4) the need for additional research.
Since the BSC’s recommendations were made, still more concerns have been raised about the monograph, this time about the validity of several studies upon which the report’s conclusions were based. NTP staff are currently making those revisions; a final report has yet to be released.
Other Studies Offer Insights
In 2021, a study from Spain found that mothers’ prenatal fluoride exposure was associated with higher cognitive scores in boys at age 4, not lower. There was no difference in girls’ IQ. This contradicts the findings of the 2019 Canadian study. A much larger 2022 study in Australia followed boys and girls with different lifetime fluoride exposures from birth to age 5. This study assessed the children’s emotional and behavioral development until they reached age 18. Their conclusion? Exposure to fluoridated water during the first five years of life was not associated with altered measures of child emotional and behavioral development or executive functioning.
More than 6,800 studies and research papers have been produced fluoride in water, and the overwhelming evidence shows that fluoride is safe and beneficial. Water fluoridation has been and continues to be thoroughly evaluated to ensure the health of those who are fortunate to live in a fluoridated community.
