Since 1945, fluoride has been added to community drinking water systems in the United States to prevent tooth decay. Currently, 73% of the U.S. population receives fluoridated water at a targeted concentration of 0.7 milligrams per liter. However, a new study suggests that prenatal exposure to fluoride at these levels may increase the risk of neurobehavioral problems in children.
The research, published in Opening of the JAMA networkfound that a 0.68 milligram per liter increase in fluoride exposure during pregnancy was associated with nearly a doubling of the risk that a child would have neurobehavioral problems by age three.
Fluoride is a mineral that occurs naturally in water, soil, and various foods. In teeth, fluoride helps rebuild (remineralize) weakened tooth enamel, making it more resistant to acid attacks from bacteria in the mouth. This process helps prevent cavities from forming.
Fluoride, however, may impact neurodevelopment due to its ability to cross the placental barrier and reach the developing fetus. Animal studies have shown that high levels of fluoride exposure cause neurobiochemical changes, such as oxidative stress, disruption of neurotransmitter function, and alterations in cell signaling pathways.
Recent studies from Mexico and Canada have shown that even lower levels of fluoride exposure, similar to those seen in the United States, may be linked to poorer neurodevelopmental outcomes. These studies have shown associations between higher prenatal fluoride exposure and lower IQ, increased symptoms of attention-deficit/hyperactivity disorder, and poorer cognitive functioning.
However, research on this topic in the United States is lacking. Researchers sought to fill this gap by examining whether prenatal fluoride exposure is associated with neurobehavioral outcomes in children in the United States.
“There is no known benefit of fluoride consumption for fetal development, but we do know there may be a risk to their developing brain,” said Ashley Malin, the study’s lead researcher and an assistant professor at the University of Florida.
The study included 229 mother-child pairs from the Maternal and Developmental Risks from Environmental and Social Stressors (MADRES) cohort. This cohort is comprised primarily of Hispanic women of low socioeconomic status living in urban Los Angeles, California. Participants were recruited at prenatal care visits between 2015 and 2020, with eligibility criteria including 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, researchers collected spot urine samples from mothers during their third trimester of pregnancy. These samples were analyzed to determine urinary fluoride levels, which provide a reliable measure of total fluoride intake. The measurements were adjusted for specific gravity to account for variations in urinary concentration. The mean gestational age at the time of urine collection was approximately 31.6 weeks.
When children reached 36 months of age, their mothers completed the Preschool Child Behavior Checklist (CBCL), a widely used parent-report measure of child neurobehavior. The CBCL includes 99 items that assess a range of behavioral and emotional problems, such as reactive emotional disorders, anxious-depressive disorders, somatic complaints, withdrawal, sleep problems, attention problems, and aggressive behavior.
The checklist also includes scales consistent with Diagnostic and Statistical Manual of Mental Disorders (DSM-5) categories, including depressive problems, anxiety problems, oppositional defiant problems, autism spectrum problems, and attention-deficit/hyperactivity disorder problems.
The study found that the median urinary fluoride concentration in mothers was 0.76 milligrams per liter. A key finding was that an increase of 0.68 milligrams per liter in maternal urinary fluoride levels during pregnancy was associated with nearly twice the odds that the child would have a clinical borderline or clinical score for all neurobehavioral problems.
Specifically, this increase in fluoride exposure was linked to a 2.29-point increase in internalizing problems, such as emotional reactivity, anxiety, and somatic complaints, and a 2.14-point increase in total neurobehavioral problems.
In addition to the general increase in neurobehavioral problems, higher fluoride exposure was also associated with specific behavioral problems. For example, an increase of 0.68 milligrams per liter of fluoride was linked to a 13.54% increase in emotionally reactive behavior scores and a 19.60% increase in somatic complaints. In addition, there were significant associations with DSM-5-oriented scales, including an 11.29% increase in anxiety problems and an 18.53% increase in autism spectrum problems.
“Women whose bodies were exposed to higher levels of fluoride during pregnancy tended to rate their 3-year-old children higher on general neurobehavioral problems and internalizing symptoms, including emotional reactivity, anxiety and somatic complaints,” said Tracy Bastain, associate professor at the University of Southern California and lead author of the study.
The study did not find a significant link between fluoride exposure and externalizing problems, such as aggressive behavior and attention problems. Additionally, the researchers observed no interaction between fluoride exposure and child sex, indicating that the associations were consistent in both boys and girls.
The results of this study suggest that prenatal exposure to fluoride, even at levels considered optimal for preventing dental caries, may be associated with an increased risk of neurobehavioral problems in children. The researchers noted that the fluoride levels found in the study participants’ samples are typical of people living in communities where water is fluoridated.
Variations in a person’s fluoride exposure can be attributed to differences in dietary habits, such as using tap water for drinking and cooking instead of filtered water, and consuming foods and beverages that are naturally high in fluoride. These include green and black tea, some seafood, and foods treated with fluoride-containing pesticides.
There are currently no formal guidelines to limit fluoride intake during pregnancy. Given the widespread use of fluoridated water, these findings highlight the need for further research to confirm these findings and better understand the potential risks of fluoride exposure.
“I think this is important evidence, given that this is the first study in the United States and the results are quite consistent with other studies published in North America with comparable levels of fluoride exposure,” Malin said. “It would be important to do a national study on this topic in the United States, but I think the results of the current study and the recent studies in Canada and Mexico suggest that there is a real concern about this.”
The study, “Maternal Urinary Fluoride and Child Neurobehavior at Age 36 Months,” was authored 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.