Fluoride has been added to community drinking water systems in the United States since 1945 to prevent dental cavities. 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 fluoride exposure at these levels may increase the risk of neurobehavioral problems in children.
The research, published in JAMA Network Open, found that a 0.68 milligram per liter increase in fluoride exposure during pregnancy was associated with nearly double the chance of a child exhibiting neurobehavioral issues at age three.
Fluoride is a naturally occurring mineral found in water, soil, and various foods. In teeth, fluoride helps to rebuild (remineralize) weakened tooth enamel, making it more resistant to acid attacks from bacteria in the mouth. This process helps prevent the formation of cavities.
But fluoride might impact neurodevelopment due to its ability to cross the placental barrier and reach the developing fetus. High levels of fluoride exposure have been shown in animal studies to cause neurobiochemical changes, such as oxidative stress, disruption of neurotransmitter function, and alterations in cellular signaling pathways.
Recent studies in Mexico and Canada have indicated that even lower levels of fluoride exposure, similar to those found in the United States, might 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, U.S.-based research on this topic has been lacking. The researchers aimed to address 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 to the developing fetus, but we do know that there is possibly a risk to their developing brain,” said the study’s lead investigator Ashley Malin, an assistant professor at the University of Florida.
The study involved 229 mother-child pairs from the Maternal and Developmental Risks from Environmental and Social Stressors (MADRES) cohort. This cohort consists predominantly of Hispanic women of low socioeconomic status living in urban Los Angeles, California. The participants were recruited during prenatal care visits between 2015 and 2020, with eligibility criteria including being 18 years 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 spot urine samples from the mothers during their third trimester of pregnancy. These samples were analyzed for urinary fluoride levels, which provide a reliable measure of total fluoride intake. The measurements were adjusted for specific gravity to account for variations in urine concentration. The mean gestational age at the time of urine collection was approximately 31.6 weeks.
When the children reached the age of 36 months, their mothers completed the Preschool Child Behavior Checklist (CBCL), a widely used parent-reported measure of child neurobehavior. The CBCL includes 99 items that assess a range of behavioral and emotional problems, such as emotionally reactive, anxious-depressed, somatic complaints, withdrawn, sleep problems, attention problems, and aggressive behavior.
The checklist also includes scales consistent with the 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 among the mothers was 0.76 milligrams per liter. A key finding was that a 0.68 milligram per liter increase in maternal urinary fluoride levels during pregnancy was associated with nearly double the odds of the child scoring in the borderline clinical or clinical range for total 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 overall increase in neurobehavioral problems, higher fluoride exposure was also associated with specific behavioral issues. For instance, a 0.68 milligram per liter increase in fluoride was linked to a 13.54% increase in scores for emotionally reactive behaviors and a 19.60% increase in somatic complaints. Furthermore, 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 with higher fluoride exposure levels in their bodies during pregnancy tended 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 senior author of the study.
The study did not find significant associations between fluoride exposure and externalizing problems, such as aggressive behavior and attention problems. Additionally, the researchers did not observe any interaction between fluoride exposure and the child’s sex, indicating that the associations were consistent across both boys and girls.
The findings from this study suggest that prenatal fluoride exposure, even at levels considered optimal for preventing dental cavities, may be associated with an increased risk of neurobehavioral problems in children. The researchers emphasized that the fluoride levels found in the study participants’ samples are typical for people living in communities with fluoridated water.
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 naturally high in fluoride. These include green and black tea, certain seafoods, and foods treated with fluoride-containing pesticides.
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 to better understand the potential risks of fluoride exposure.
“I think this is important evidence, given that it’s the first U.S.-based study and findings are quite consistent with the other studies published in North America with comparable fluoride exposure levels,” Malin said. “Conducting a nationwide U.S. study on this topic would be important, but I think the findings of the current study and recent studies from Canada and Mexico suggest that there is a real concern here.”
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.