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Babies whose mothers drank fluoridated water during pregnancy at and slightly below concentrations currently recommended by U.S. public health agencies scored lower on tests that measure fluid cognition — the ability to think logically and solve problems in new situations.
Fluid cognition is considered the “cornerstone of human cognition, both during development and in adulthood.”
A new study led by Columbia University researchers found that prenatal fluoride exposure resulted in reduced fluid cognition at levels as low as 0.675 milligrams per liter (mg/L).
That’s slightly below the U.S. Public Health Service’s recommended concentration of 0.7 mg/L for fluoridated drinking water and far below the U.S. Environmental Protection Agency’s (EPA) maximum contaminant level of 4 mg/L and the World Health Organization’s guideline of 1.5 mg/L, according to the study.
The study, funded by the National Institutes of Health (NIH) and accepted for publication in the American Journal of Epidemiology, analyzed outcomes among 2,514 children born between 2006 and 2019 at 17 sites spanning 23 U.S. states that are part of the Environmental influences on Child Health Cohort (ECHO).
The authors concluded that more research is needed to identify the risky prenatal, postnatal and childhood window when fluoride exposure can harm cognitive development.
Higher fluoride linked to lower fluid cognition
To estimate prenatal water fluoride exposure, the researchers linked publicly available drinking water fluoride measurements to residential address information collected during pregnancy. The study focused only on fluoride from drinking water and did not account for any other sources.
The researchers then compared estimated fluoride intake with children’s cognitive abilities, evaluated using the NIH Toolbox Cognition Battery.
Researchers separately examined “fluid cognition,” which included measures of cognitive flexibility, inhibitory control, attention and memory, and “crystallized cognition,” assessed through a vocabulary test.
Crystallized cognition is “the breadth and depth of knowledge, vocabulary, and verbal skill a person has acquired through education, experience, and cultural exposure — what has been learned and can be retrieved and applied later.”
The children whose mothers were exposed to higher fluoride levels during pregnancy tended to score lower on the fluid cognition tests.
They found children’s cognition was affected when mothers were exposed to water fluoride levels at and above 0.675 mg/L, or 675 micrograms per liter. That’s below the federally recommended level for water fluoridation.
They also found that every 500 microgram-per-liter increase in water fluoride was linked to an average 3.36-point drop in IQ.
The outcomes were substantially worse among children whose cognitive abilities were assessed before age 7. Their IQ scores dropped up to 13.5 points for the same increase in water fluoride content.
The researchers cautioned, however, that the apparent difference by age requires further study.
“This study adds to a large body of work that looks at how early exposure to environmental contaminants may be associated with the development of the thinking and learning processes that are important for children’s developmental outcomes,” co-senior author Amy Margolis, Ph.D., of The Ohio State University College of Medicine said in a Columbia University press release about the study.
“Continuing to study fluoride and other exposures will be integral in best supporting children’s environmental health and well-being.”
Malin and Thiessen both noted that a limitation of the study was that they didn’t measure individual fluoride intake. Because intake can vary across individuals, failure to measure individual exposure can lead to exposure misclassification.
“Despite this, the authors still observed quite sizable associations between prenatal public water fluoride exposure and child fluid cognition, particularly for children younger than 7,” Malin said.
“Nevertheless, true associations between prenatal fluoride exposure and child cognition may in fact be larger than what this study was able to detect,” she added. “Future individual-level research will be needed to further investigate that question.”
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Findings add to evidence in contested court ruling
Water fluoridation in the U.S. has been a political flashpoint since a landmark 2024 federal court ruling concluded that current levels of fluoride added to water at 0.7 mg/L posed a risk to children’s health. The ruling directed the EPA to regulate the chemical under the Toxic Substances Control Act.
The ruling was largely based on the federal National Toxicology Program’s (NTP) six-year assessment of all existing literature on fluoride and neurotoxicity, along with testimony from leading experts at top universities across the world who study the issue.
The NTP concluded that water fluoridation at 1.5 mg/L was linked to lower IQ in children. It also found that people exposed to water fluoridation below 1.5 mg/L could have high fluoride levels in their systems, in part because people can be exposed to fluoride from other sources and/or may drink different amounts of water.
The NTP researchers said their findings about water fluoridation and neurotoxicity were based on studies of water fluoridation at or above current U.S. fluoridation levels.
The groups that sued the EPA also argued that EPA regulations for other toxic chemicals don’t allow exposure at known toxicity levels. For other chemicals, exposure is allowed only at levels that are at least 10 times the known toxic exposure level to ensure safety.
An appeals court later overturned the fluoride verdict on a procedural issue, but the court did not disagree with the lower court ruling that fluoridation at current levels poses an unreasonable risk to human health.
The American Dental Association, mainstream media and others have attempted to publicly discount the NTP’s findings, arguing that its data were weak at current levels, or that studies showing the neurological effects of water fluoridation happened in other countries that weren’t similar to the U.S.
The new Columbia University study — conducted in the U.S. at current fluoridation levels — confirmed the NTP’s conclusions and offered findings in line with other recent studies in the U.S.
Ashley Malin, Ph.D., assistant professor of epidemiology at the University of Florida’s College of Medicine, and lead author of a U.S. study that linked fluoride exposure during pregnancy to neurobehavioral problems in children, told The Defender that the Columbia University study is “significant” because it includes a relatively recent cohort of children from multiple U.S. states.
She said the findings were consistent with other major cohort studies in Mexico and Canada that observed an inverse association between early life fluoride exposure and non-verbal IQ.
Kathleen Thiessen, Ph.D., who co-authored the 2006 National Research Council study on fluoride toxicity, also said the study was consistent with many recent findings.
“Importantly, they see an adverse effect at lower levels of water fluoride than many previous studies have used, and these are U.S. children,” she said.
Related articles in The Defender
- Breaking: Fluoride in Water Poses ‘Unreasonable Risk’ to Children, Federal Judge Rules
- Breaking: Federal Court Strikes Down Landmark Fluoride Ruling on Technicality — ‘Not the Science’
- Children Whose Mothers Were Exposed During Pregnancy to Fluoridated Tap Water at Higher Risk of Neurobehavioral Problems
- CDC Stands by Water Fluoridation After Report Linking Fluoride to Lower IQs in Kids Finally Published
- The Debate Is Over: Fluoride Is Harmful to Pregnant Moms, Kids
