Three-quarters of households in the U.S. have drinking water with fluoride added to it. The purpose for the practice, which began around 1945, is to help prevent tooth decay. The good news is that it works. Kids — and adults — do have fewer cavities. The appears to be a downside, however — a connection between social, emotional and behavioral issues in children and prenatal fluoride levels.

Researchers from the Keck School of Medicine at the University of Southern California (USC) used data gathered from the Maternal and Developmental Risks from Environmental and Social stressors (MADRES) Center for Environmental Health Disparities program at Keck. MADRES follows predominantly Hispanic families in Los Angeles from pregnancy throughout childhood.

Children born to mothers exposed to more fluoride had more problems with headaches, stomach aches, anxiety and symptoms linked to autism.

The study analyzed fluoride levels in 229 mother-child pairs. Fluoride levels were measured using urine samples collected during the third trimester of pregnancy. The researchers also looked at the child's behavior at the age of three.

The results are disturbing. A mere 0.68 milligram per liter increase in fluoride exposure was linked to nearly a double likelihood of a child showing neurobehavioral problems in a range that is close to, or at level, to meeting the criteria for a clinical diagnosis. In fact, children whose mothers were exposed to this level of fluoride during pregnancy were 1.83 times more likely to show behavioral problems considered to be clinically significant.

“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,” Tracey Bastain, senior author of the study and an associate professor of Clinical Population and Public Health Sciences at USC's Keck School of Medicine and co-director of MADRES, said in a press release.

Specifically, children exposed to more fluoride had more problems with headaches, stomach aches, anxiety and symptoms linked to autism.

The recent findings add to evidence from animal studies that showed fluoride can harm neurodevelopment. There's also data from studies that took place in Canada, Mexico and other countries, pointing to a connection between prenatal exposure to fluoride and a lower IQ in early childhood.

“There are no known benefits to the fetus from ingesting fluoride,” said Ashley Malin, lead author of the present study. Malin conducted the research in part as a postdoctoral scholar at the Keck School of Medicine. She is now an assistant professor of epidemiology at the University of Florida's College of Public Health and Health Professions and College of Medicine.

The research team is planning to explore how exposure to fluoride during pregnancy may impact brain development among infants in the MADRES study. Said Bastain, “…[M]ore studies are urgently needed to understand and mitigate the impacts in the entire U.S. population.”

If you're concerned about drinking water with fluoride during pregnancy, one way to reduce the fluoride in your drinking water is to use a reverse osmosis water filter. This kind of filter is typically installed under the kitchen sink. Another option is to use a tabletop plastic pitcher which filters out fluoride and metals, too.

The study can be found in JAMA Network Open.