Fluoride during pregnancy increases risk of neurobehavioral problems in children

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

A new study by researchers at the Keck School of Medicine of the University of Southern California analyzed more than 220 mother-child pairs, collecting data on fluoride levels during pregnancy and the 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 the child would exhibit neurobehavioral problems at levels close to 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, PhD, associate professor of clinical population and community sciences and senior author of the study.

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

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

"This is the first study conducted in the U.S. 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 for those living in areas with fluoridated water in North America," said Ashley Malin, PhD, associate professor of epidemiology in the University of Florida College of Public Health and Health Sciences and senior author of the current 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 came from the Maternal and Child 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.

The researchers analyzed 229 mother-child pairs, calculating fluoride exposure from urine samples collected in the third trimester of pregnancy. Most of the 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 a child's social and emotional functioning.

Children exposed to an additional 0.68 milligrams of fluoride per liter in the womb were 1.83 times more likely to show behavioral problems considered clinically significant or near clinically significant. Specifically, children exposed to more fluoride had more problems with emotional reactivity, somatic complaints (such as headaches and abdominal pain), 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 U.S. population There are currently no official recommendations to limit fluoride intake during pregnancy, but the researchers hope these findings will help spur change.

"There are no known benefits to the fetus from fluoride exposure," Malin said. "And yet we now have several studies from North America that suggest there may be quite significant risks to the developing brain at this time."

Next, the research team will study how fluoride exposure during pregnancy may affect brain development in babies in the MADRES study. Additional studies in other parts of the country could also help determine the extent of the problem and the best path forward, Bastain said.

"While this is the first U.S. study examining fluoride exposure during pregnancy, more research is needed to understand and mitigate the effects for the overall U.S. population," she said.

The results of the study were published in JAMA Network Open.