Children Whose Mothers Were Exposed During Pregnancy to Fluoridated Tap Water at Higher Risk of Neurobehavioral Problems

Dr. Howard Hu, co-author of a study published today in JAMA Network Open, said the study’s findings are concerning because the women were not exposed to particularly high levels of fluoride.

by Brenda Baletti, Ph.D.

Children born to women exposed during pregnancy to fluoridated drinking water were more likely to have neurobehavioural problems, according to a study published today in JAMA Network Open.

In the first U.S.-based cohort study to examine this link, researchers from the Keck School of Medicine at the University of Southern California (USC), the University of Florida and Indiana University followed 229 mother-child pairs from pregnancy until the children were 3 years old.

They found that a 0.68 milligram per liter (mg/L) increase in fluoride exposure during pregnancy was associated with nearly double the chance of a child, by age 3, exhibiting neurobehavioral problems at or near a level that meets the criteria for a clinical diagnosis.

Dr. Howard Hu, Flora L. Thornton Chair and Professor of Population and Public Health Sciences at USC and co-author of the study told The Defender the study’s findings are concerning because the women were not exposed to particularly high fluoride levels.

Their fluoride exposure came primarily from fluoridated tap water in Los Angeles, which has water fluoridation at 0.7 mg/L — typical for fluoridation levels in most U.S. cities and towns and approximately the same level found to have effects in the study.

“When you add this to all the other studies that have been done on this subject in the last few years,” Hu said, “it creates a body of evidence, which — in conjunction with the basic science looking at how fluoride may be toxicologically active on the brain — suggests that the impact of fluoride on neurobehavioral development problems is causal. It’s not just an epidemiological association.”

The authors concluded that it may be necessary to “establish recommendations for limiting exposure to fluoride from all sources during the prenatal period, a time when the developing brain is known to be especially vulnerable to injury from environmental insults.”

Recent debates on U.S. water fluoridation

Following the advice of public health agencies, most U.S. towns and cities have been adding fluoride to their water systems since 1945. Today’s recommended target rate is 0.7 mg/L.

Community water fluoridation practices have long been celebrated as one of the “great public health achievements” of the 20th century. The Centers for Disease Control and Prevention (CDC) defends the practices as key to public health.

However, a growing body of research establishing that fluoride negatively affects neurodevelopment has led scientists and the public to question water fluoridation over the last several years.

In 2006, after concluding in a multiyear study that fluoride could interfere with brain function, the National Research Council (NRC) called for more research.

Since then major cohort studies in Mexico and Canada have linked fluoride exposure to lower IQ scores and other neurodevelopmental issues in children.

Cohort studies, in which researchers collect epidemiological data during pregnancy and then from children over their lifetimes to study a variety of health outcomes tied to environmental exposures, are the gold standard of epidemiological studies.

Last year, after years of research, peer review, and attempts by public officials at the U.S. Department of Health and Human Services (HHS) to block publication, the National Toxicology Program (NTP) — the interagency government program that studies environmental toxins — published a draft systematic review of the literature on fluoride and neurotoxicity in children.

The NTP report found that neonatal and childhood fluoride exposure had negative cognitive and neurodevelopmental effects for children. That report concluded that fluoride had neurotoxic effects for children at 1.5 mg/L.

The NTP also identified high-quality studies linking fluoride to lower IQ at lower levels and called for more research in this area.

Hu said the JAMA study bolsters the NTP’s findings.

Debates over water fluoridation and the NTP’s findings have focused on the level at which that exposure becomes a concern.

In an ongoing landmark trial, several environmental and consumer watchdog groups are suing the U.S. Environmental Protection Agency (EPA), arguing that water fluoridation at existing levels threatens human health and that water fluoridation ought to be ended or much more strictly regulated.

Despite the recent studies and the NTP’s findings, the EPA maintained in court that there is insufficient evidence that fluoride poses a neurodevelopmental risk to children to warrant changing or ending current water fluoridation policy recommendations.

The fluoride lobby and many officials in public health agencies defend the EPA’s opinion. However, the surgeon general’s office notably stopped issuing public statements supporting water fluoridation after the NTP published its report.

Michael Connett, the attorney representing the plaintiffs in the case against the EPA, told The Defender the JAMA study is a “huge SOS signal on fluoride” for the U.S.

“The question in our court case was whether adding fluoridation chemicals to drinking water presents an unreasonable risk of neurodevelopmental harm,” he said. “This study provides the most direct evidence to date that it does.”

Connett said the JAMA study “provides further corroboration that early life exposure to fluoride can adversely affect brain development, and suggests millions of people in the U.S. are unknowingly suffering the consequences.”

Risk analysis scientist Kathleen Theissen, Ph.D., who was not involved with the study but co-authored the 2006 NRC study on fluoride toxicity, told The Defender the new study is “extremely important,” because it shows “increased likelihood of neurobehavioral problems with increased maternal fluoride exposure, for a cohort of children in the United States with relatively low maternal fluoride exposures.”

It adds to the large and growing body of data on fluoride’s neurotoxicity and supports arguments to limit exposure of the U.S. population to the chemical, Theissen said.

Why does anybody still think water fluoridation is a good idea?

The JAMA study analyzed data from the Maternal and Developmental Risks from Environmental and Social Stressors (MADRES) pregnancy cohort study, which consisted of predominantly low-income Latina women in Los Angeles.

The EPA, the National Institutes of Health and the National Institute of Environmental Health Sciences funded the study.

Between 2017 and 2020, 229 mothers took a test to measure the fluoride concentration in their urine during the third trimester of pregnancy. Maternal urinary fluoride levels are considered a good measure of fluoride exposure for both mother and baby because fluoride passes through the placental barrier.

The median maternal urinary level in the study was 0.76 mg/L.

Between 2020 and 2023, the mothers completed a 99-question survey, the Preschool Child Behavior Checklist, to assess their child’s behavior at age 3. The test measures children’s “internalizing” or inwardly focused problems, like emotional reactivity and anxiety, and “externalizing” or outwardly focused problems like hyperactivity and aggression. It also provides a measure of overall total behavioral problems.

The survey asks questions about general behaviors such as restlessness, difficulty paying attention, hyperactivity, or being clingy or accident-prone. It also asks about specific behaviors, like being overly concerned with neatness, exhibiting cruelty to animals, or chewing on things that aren’t edible. It asks whether children have health problems with no clear medical cause, like rashes, cramps and headaches.

The researchers statistically controlled for other social, cultural and economic issues, such as maternal age, education, health factors, household income, ethnicity and structural racism, that could affect behavioral outcomes, and for lead exposure.

They found that a 0.68 mg/L increase in maternal urinary fluoride levels was associated with nearly double the odds of having a total problems score that came close to or met the criteria for a clinical diagnosis. It showed a statistically significant increase in internalizing problem and total problem scores.

The increase in maternal urinary fluoride was also associated with higher externalizing problems scores — showing behaviors like aggression in the classroom or with other children — but the results were not statistically significant.

When the researchers examined the association of maternal urinary fluoride with the raw scores for different syndromes assessed by test, they found a 13.54% increase in emotional reactivity, a 19.6% increase in somatic issues, an 11.29% increase in anxiety problems and an 18.53% increase in problems on the autism spectrum.

Thiessen said it is important that this study was published in JAMA, which is considered a top medical journal.

Earlier work on fluoride published in JAMA in 2019 found that higher levels of fluoride exposure during pregnancy led to reduced IQ in children by ages 3 and 4. That paper received much more detailed scrutiny by reviewers than is usual for JAMA papers, plus an editorial explaining why the journal chose to publish the article, she said.

“Given the potentially controversial nature of the new paper, it is likely that it also received extra scrutiny. The fact that JAMA published the 2019 article and the recent article indicates that the editors and reviewers consider each of the articles to be of very high quality and importance.”

Theissen added:

“Actually, given the quality and size of the current body of evidence on fluoride neurotoxicity, as well as other adverse health effects, the question is not whether Malin et al.’s paper [today’s study] should be considered controversial, but why anybody still thinks community water fluoridation is a good idea!”