Fluoride during pregnancy increases the risk of neurobehavioral problems in children

Nearly three-quarters of the United States population receives drinking water containing fluoride, a practice that began in 1945 to prevent tooth decay. But recent research suggests that fluoride exposure may cause harm to the fetus if it is consumed during pregnancy, a critical period for brain development.

A new study led by researchers at the Keck School of Medicine at the University of Southern California analyzed more than 220 mother-child pairs, collecting data on fluoride levels during pregnancy and children's behavior at age three. The researchers found that an increase in fluoride exposure of 0.68 milligrams per liter was associated with a nearly doubled likelihood that a child would exhibit neurobehavioral problems at levels approaching a clinical diagnosis.

"Women with higher levels of fluoride exposure in their bodies during pregnancy tend 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, Ph.D., associate professor. Clinical population and social sciences and senior author of the study.

These population-based findings complement existing data from animal studies showing that fluoride may harm neurodevelopment, as well as data from studies in Canada, Mexico and other countries showing that prenatal fluoride exposure is associated with lower IQ levels in early childhood.

Researchers hope the new findings will help communicate the risks of fluoride consumption during pregnancy to lawmakers, health care providers and the public.

"This is the first study conducted in the United States to examine this association. Our results are remarkable given that the women in this study were exposed to fairly low levels of fluoride—levels that are typical of those living in regions with fluoridated water in North America.", said Ashley Malin, Ph.D., assistant professor of epidemiology in the University of Florida College of Public Health and Health Sciences and Medicine and senior author of this study.

Malin conducted the research in part as a postdoctoral fellow at the Keck School of Medicine.

Tracking Emotions and Behavior Data for the study were obtained from the Maternal and Infant Risk from Environmental and Social Stressors (MADRES) Center at the Keck School of Medicine. MADRES follows predominantly Hispanic families in Los Angeles from pregnancy through childhood.

“The overall goal of MADRES is to reduce the impact of environmental pollutants on the health and well-being of marginalized communities,” said Bastain, who is co-director of MADRES.

Researchers analyzed 229 mother-child pairs, calculating fluoride exposure from urine samples collected during the third trimester of pregnancy. Most urine samples were collected from fasting women, which increases the accuracy of the chemical analysis. The children were then assessed at age three using the Preschool Behavior Checklist, which uses parent reports to assess the child's social and emotional functioning.

Children exposed to an additional 0.68 milligrams of fluoride per liter in utero were 1.83 times more likely to show behavioral problems considered clinically significant or near clinically significant. Specifically, children with greater fluoride exposure had more problems with emotional reactivity, somatic complaints (such as headaches and stomach pains), anxiety, and autism-related symptoms.

No association was found with several other neurobehavioral symptoms, including “externalizing behaviors” such as aggression and attention problems.

Impact on the US Population There are currently no official recommendations for limiting fluoride intake during pregnancy, but researchers hope these findings will help spur change.

"There is no known benefit to the fetus from fluoride use," Malin said. "And yet we now have several studies from North America that suggest there may be quite a significant risk to the developing brain at this time."

The research team will next study how exposure to fluoride during pregnancy may affect brain development in infants in the MADRES study. Additional research in other regions of the country could also help determine the extent of the problem and the best path forward, Bastain said.

"Although this is the first study conducted in the United States to examine fluoride exposure during pregnancy, more research is needed to understand and mitigate the effects across the entire U.S. Population," she said.

The study results were published in JAMA Network Open.