Fluoride has been added to community drinking water systems in the United States since 1945 to prevent tooth decay. Currently, 73 percent of the American population receives fluoridated water at the target of 0.7 milligrams per liter. However, new research suggests that prenatal fluoride exposure at these levels may increase the risk of neurobehavioral problems in children.
The study, published in JAMA Network OpenThey found that an increase in fluoride exposure of 0.68 milligrams per liter during pregnancy nearly doubled the likelihood that a child would exhibit neurobehavioral issues by age three.
Fluoride is a naturally occurring mineral found in water, soil and various foods. Fluoride in the teeth helps to rebuild (remineralize) weakened tooth enamel, making it more resistant to acid attacks from bacteria in the mouth. This process helps prevent pits from forming.
However, fluoride has the ability to cross the placental barrier and reach the developing fetus, potentially affecting neural development. In animal studies, exposure to high levels of fluoride has been shown to cause neurological biochemical changes such as oxidative stress, disruption of neurotransmitter functions and changes in cellular signaling pathways.
Recent studies in Mexico and Canada suggest that low levels of fluoride exposure, similar to those found in the United States, may be linked to poor neurodevelopmental outcomes. These studies have shown an association between high prenatal fluoride exposure and lower IQ, symptoms of attention deficit/hyperactivity disorder, and poorer cognitive function.
However, there is no US-based research on this topic. 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 to the developing fetus from consuming fluoride, but we do know there is a risk to their developing brain,” said Ashley Malin, an assistant professor at the University of Florida.
The study involved 229 mother-child pairs from the Maternal and Developmental Risks of Environmental and Social Stress (MADRES) cohort. This group consisted primarily of low socioeconomic status Hispanic women living in Los Angeles, California. Participants were recruited during prenatal care visits between 2015 and 2020, eligibility criteria were 18 years or older, less than 30 weeks pregnant at the time of recruitment, and fluent in English or Spanish.
The researchers collected single-spot urine samples from mothers during the third trimester of pregnancy to assess fluoride exposure. These samples are analyzed for urine fluoride levels, which provide a reliable measure of total fluoride levels. Taking into account the difference in urine, the measurements are adjusted for specific gravity. The average gestational age at the time of urine collection is approximately 31.6 weeks.
When the children were 36 months old, 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 various behavioral and emotional problems such as emotional reactivity, anxiety-depression, emotional complaints, alienation, sleep problems, attention problems, and aggressive behaviors.
The checklist also includes scales consistent with the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) categories, including depression, anxiety disorders, oppositional defiant disorders, autism spectrum disorders, and attention-deficit/hyperactivity disorder.
The study found that the median urinary fluoride level among mothers was 0.76 milligrams per liter. A key finding was that an increase of 0.68 milligrams per liter of maternal urine fluoride during pregnancy was associated with a doubling of the child’s risk of total neurobehavioral problems in the borderline clinical or clinical range.
Specifically, this increase in fluoride exposure was associated with a 2.29-point increase in internalizing problems such as emotional reactivity, anxiety, and somatic complaints, and a 2.14-point increase in general neurobehavioral problems.
In addition to an increase in general neurobehavioral problems, high fluoride exposure has been linked to certain behavioral issues. For example, an increase of 0.68 milligrams per liter of fluoride was associated with a 13.54% increase in emotional response behaviors and a 19.60% increase in somatic complaints. Additionally, there were significant associations with DSM-5-oriented scales, including an 11.29% increase in anxiety disorders and an 18.53% increase in autism spectrum disorders.
“Women with higher exposure to fluoride in their bodies during pregnancy are more likely to have 3-year-old children with more general neurobehavioral problems and increased symptoms of internalizing, emotional reactivity, anxiety, and somatic complaints,” Associate Professor Tracy Bastine said. 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. In addition, the researchers did not notice any interaction between fluoride exposure and the gender of the child, which shows that the associations are consistent between both boys and girls.
The findings of this study show that prenatal fluoride exposure, even at levels considered optimal for preventing tooth decay, increases the risk of neurobehavioral problems in children. The researchers emphasized that the levels of fluoride found in the study participants’ samples were typical for people living in communities with fluoridated water.
Differences in a person’s exposure to fluoride may be due to differences in dietary habits, such as using tap water for drinking and cooking instead of filtered water, and consuming foods and beverages rich in fluoride. These include green and black tea, certain seafood, and foods treated with fluoride-containing pesticides.
Currently, there are no standard guidelines for limiting fluoride intake during pregnancy. After widespread use of fluoridated water, these results indicate that more research is needed to confirm these findings and better understand the potential risks of fluoride exposure.
“I think it’s important evidence that this is the first US-based study, and the findings are very consistent with other fluoride exposure levels published in North America,” Malin said. “It would be useful to conduct a national US study on this topic, but the findings of the current study and recent studies in Canada and Mexico indicate that there is a real concern here.”
The study “Maternal urinary fluoride and child neurobehavior at 36 months” Authored by Ashley J. Malin, Sandra P. Eckel, Howard Hu, E. Angeles Martinez-Meier, Ixel Hernandez-Castro, Tinu Yang, Shoreh F. Farzan, Rima Habre, Kari V. Breton and Teresa M. Bastian.