Fluoride has been added to public drinking water systems in the United States since 1945 to prevent tooth decay. Currently, 73% of the U.S. population drinks fluoridated water at the target concentration of 0.7 milligrams per liter. However, new research suggests that prenatal exposure to this level of fluoride may increase the risk of neurobehavioral problems in children.
This study JAMA Network OpenThey found that an increase of 0.68 milligrams per liter of fluoride exposure during pregnancy was associated with nearly double the chances that a child would have neurobehavioral problems at age three.
Fluoride is a naturally occurring mineral found in water, soil, and many foods. In teeth, fluoride helps rebuild (remineralize) weakened tooth enamel, making it more resistant to acid attack by bacteria in the mouth. This process helps prevent cavities from forming.
However, fluoride can cross the placenta and reach fetal development, potentially affecting neurodevelopment. Animal studies have shown that exposure to high concentrations of fluoride induces neurobiochemical changes, including oxidative stress, disruption of neurotransmitter function, and alterations in cell signaling pathways.
Recent studies in Mexico and Canada have shown that even lower levels of fluoride exposure, similar to those found in the U.S., may lead to poor neurodevelopment. These studies have shown an association between higher prenatal fluoride exposure and lower IQ, increased symptoms of attention-deficit hyperactivity disorder, and poorer cognitive function.
However, there is a lack of research on this topic in the U.S. These researchers aimed to fill this gap by examining whether prenatal fluoride exposure is associated with neurobehavioral outcomes in U.S. children.
“We don’t know whether fluoride intake is beneficial for fetal development, but we do know that it may pose a risk to fetal brain development,” said Ashley Mullin, lead researcher on the study and an assistant professor at the University of Florida.
The study involved 229 mother-infant pairs from the Maternal and Child Developmental Risks from Environmental and Social Stressors (MADRES) cohort, a predominantly low socioeconomic Hispanic cohort living in urban Los Angeles, California. Participants were recruited at prenatal visits between 2015 and 2020 and eligibility requirements included being 18 years of age or older, less than 30 weeks pregnant at the time of recruitment, and fluent in English or Spanish.
To assess fluoride exposure, the researchers collected single-site urine samples from mothers during the third trimester of pregnancy. These samples were analyzed for urinary fluoride concentration, which is a reliable indicator of total fluoride intake. Measurements were adjusted for specific gravity to account for variability in urine concentration. The average gestational age at the time of urine collection was approximately 31.6 weeks.
When children were 36 months of age, mothers completed the Preschool Child Behavior Checklist (CBCL), a widely used parent-report measure of children’s neurobehavior.The CBCL contains 99 items assessing a range of behavioral and emotional problems, including emotional reactivity, anxiety/depression, somatic complaints, social withdrawal, sleep problems, attention problems, and aggressive behavior.
The checklist also includes measures that align with Diagnostic and Statistical Manual of Mental Disorders (DSM-5) categories, including depressive problems, anxiety disorders, oppositional defiant disorder, autism spectrum disorder, and attention-deficit hyperactivity disorder.
The study found that the median urinary fluoride concentration in mothers was 0.76 milligrams per liter. The key finding was that an increase of 0.68 milligrams per liter in maternal urinary fluoride concentrations during pregnancy was associated with a nearly doubling of the odds that a child would be in the borderline or clinical range for overall neurobehavioral problems.
Specifically, increased fluoride exposure was associated with a 2.29-point increase in internalizing problems, including emotional reactivity, anxiety, and somatic complaints, and a 2.14-point increase in overall neurobehavioral problems.
In addition to an overall increase in neurobehavioral problems, increased fluoride exposure was also associated with specific behavioral problems. For example, a 0.68 milligrams per liter increase in fluoride was associated with a 13.54% increase in emotionally reactive behavior scores and a 19.60% increase in somatic complaints. Additionally, there were significant associations with DSM-5-oriented measures, including an 11.29% increase in anxiety disorders and an 18.53% increase in autism spectrum disorders.
“Women who had higher levels of fluoride exposure during pregnancy were more likely to rate their 3-year-old children higher on overall neurobehavioral problems and internalizing symptoms, including emotional reactivity, anxiety and somatic complaints,” said Tracy Bastain, an associate professor at the University of Southern California and lead author of the study.
The study found no significant associations between fluoride exposure and externalizing problems, such as aggressive behavior or attention problems. Additionally, the researchers observed no interactions between fluoride exposure and the child’s gender, indicating that the associations were consistent for both boys and girls.
The results of this study suggest that prenatal fluoride exposure, even at levels considered optimal for preventing dental caries, may be associated with an increased risk of neurobehavioral problems in children. The researchers emphasized that the fluoride levels detected in the study participants’ samples were typical of people living in areas with fluoridated water.
Differences in an individual’s fluoride exposure can be attributed to differences in dietary habits, such as using tap water rather than filtered water for drinking and cooking, and consuming foods and beverages that are naturally high in fluoride. These include green and black tea, certain seafood, and foods treated with pesticides that contain fluoride.
There are currently no formal guidelines for limiting fluoride intake during pregnancy. Given the widespread use of fluoridated water, these results highlight the need for further research to confirm these findings and better understand the potential risks of fluoride exposure.
“I think this is an important piece of evidence given that this is the first study done in the U.S. and the results are very consistent with other studies published in North America with comparable fluoride exposure levels,” Marin said. “While it will be important to do research on this issue across the U.S., I think the current findings, along with recent findings from Canada and Mexico, suggest that there is real concern here.”
the study, “Maternal urinary fluoride and neurobehavior in 36-month-old children” was written by Ashley J. Malin, Sandrah P. Eckel, Howard Hu, E. Angeles Martinez-Mier, Ixel Hernandez-Castro, Tingyu Yang, Shohreh F. Farzan, Rima Habre, Carrie V. Breton, and Theresa M. Bastain.
