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A small study published Monday suggested that higher levels of fluoride consumed during the third trimester of pregnancy were associated with a greater risk of behavioral problems in the mothers’ children at 3 years old. The authors of the study, which was funded in part by the National Institutes of Health and the Environmental Protection Agency and published in the journal JAMA Network Open, believe it is the first to examine links between prenatal fluoride exposure and child development among families living in the United States, where fluoride is often added to community water supplies to prevent dental cavities.
The study’s authors and some outside researchers said that the findings should prompt policymakers to evaluate the safety of fluoride consumption during pregnancy.
“I think it’s a warning sign,” said Dr. Beate Ritz, an environmental epidemiologist at the U.C.L.A. Fielding School of Public Health.
But other experts cautioned that the study had several important limitations that made it difficult to assess the potential effects of fluoride consumption during pregnancy.
“There is nothing about this study that alarms me or would make me recommend that pregnant women stop drinking tap water,” said Dr. Patricia Braun, a professor of pediatrics at the University of Colorado School of Medicine and a spokesperson for the American Academy of Pediatrics.
The Background
Fluoride strengthens tooth enamel, and research suggests that drinking water with added fluoride can reduce cavities by up to 25 percent. Many communities in the United States have added fluoride to their water for this reason since the 1940s, a practice widely celebrated as a major public health achievement. In 2020, 63 percent of people in the United States lived in areas with at least 0.7 milligrams per liter of fluoride in the water — considered optimal for cavity prevention — though some areas have levels that are higher, in part because of naturally high fluoride in the groundwater.
In the last few years, several studies from Mexico and Canada have suggested that fluoride exposure during pregnancy is linked to slightly lower scores on intelligence tests and other measures of cognitive function in children.
But recent studies from Spain and Denmark have found no such link.
There is a “contentious debate” about water fluoridation, acknowledged Ashley Malin, an assistant professor of epidemiology in the College of Public Health and Health Professions at the University of Florida and the lead author of the new study. The issue is currently the subject of a lawsuit filed by the nonprofit Food and Water Watch and other groups against the Environmental Protection Agency. The nonprofit claims that water fluoridation poses a risk to children’s health.
The Research
The study looked at a group of 229 predominantly low-income Hispanic pregnant women in Los Angeles who were already being followed in other research. Most of the women lived in areas with fluoridated water. The researchers measured the fluoride levels in their urine in a single test during the third trimester. Then, when their children were 3 years old, the mothers filled out the Preschool Child Behavior Checklist, a measure used to detect emotional, behavioral and social problems.
Overall, 14 percent of the children had a total score in the “borderline clinical” or “clinical” range, meaning that a doctor may want to watch or evaluate them, or provide additional support, Dr. Malin said. And on average, higher fluoride levels in the mothers’ urine were correlated with a greater risk of behavioral problems in the children. The researchers found that women with urine fluoride levels at the 75th percentile were 83 percent more likely to have children with borderline or clinically significant behavioral problems than women with levels at the 25th percentile.
The main problems reported by the mothers were emotional reactivity, which is the tendency to overreact; somatic complaints, such as headaches and stomachaches; anxiety; and symptoms linked to autism (though those symptoms alone would not be enough for an autism diagnosis).
The researchers did not find an association with other behavioral symptoms like aggression or issues with concentration.
The findings are important and add to evidence suggesting prenatal fluoride consumption may affect the developing brain, said Joseph Braun, a professor of epidemiology and the director of the Center for Children’s Environmental Health at Brown University, who was not involved in the research. That said, the increases in behavioral scores were relatively small — about two points on a scale from 28 to 100 for overall behavioral problems. It’s hard to say whether such a difference might be noticeable in an individual child, he said.
But given how widespread water fluoridation is, he added, even minor behavioral changes in individual children could have a meaningful impact on the overall population.
The Limitations
The study was relatively small and didn’t include a diverse group of women. It didn’t account for many factors that can affect child development, including genetics, maternal nutrition, home environment and community support, several experts not involved in the study said.
The data would also have been stronger if the researchers had measured fluoride in urine samples from several points of time during pregnancy and collected information on tap water, bottled water and tea consumption to better understand how each contributed to the women’s fluoride levels, experts said. Black and green teas can contain high levels of fluoride.
The Preschool Child Behavior Checklist that was used to evaluate the 3-year-olds is considered a reliable measure of child behavior. But it did not take into account the fact that symptoms can change in frequency and intensity during early childhood, said Catherine Lord, an expert on autism and related disorders at the University of California, Los Angeles medical school.
Dr. Lord, who was not involved in the fluoride research, added that the checklist is not considered a reliable way to diagnose autism.
It would also be helpful to follow the children to see if the problematic behaviors persisted beyond age 3, said Melissa Melough, an assistant professor of nutrition sciences at the University of Delaware, who was not involved in the research.
What’s Next
While the experts agreed that more robust research was needed to untangle the potential effects of prenatal fluoride exposure, they had differing opinions about the study’s bottom line.
Dr. Malin said that, based on her findings and the evidence from previous studies, it might be a good idea for women to limit fluoride intake during pregnancy, a view that was echoed by Dr. Ritz and others.
“For me, the takeaway is: Protect pregnancy,” said Marcela Tamayo-Ortiz, an environmental epidemiologist at the Columbia University Mailman School of Public Health who has studied prenatal exposures for more than two decades.
But the American Dental Association said in a statement that the organization stands by its recommendation to “brush twice a day with fluoride toothpaste and drink optimally fluoridated water.”
And Dr. Nathaniel DeNicola, an OB-GYN and environmental health expert in Orange County, Calif., said he wouldn’t advise his pregnant patients to avoid fluoridated water based on the study, because “it’s not conclusive.”
Dr. Melough said she didn’t think women should be alarmed by the findings. But, she added, while it’s clear that fluoride helps to reduce cavities, it’s possible that adding it to the water “could have some unintended consequences,” and policymakers should continually evaluate the practice as new science emerges.
You can find out what the fluoride levels are in your local water by contacting your water utility or checking the C.D.C.’s My Water’s Fluoride website. If you want to reduce your fluoride consumption, experts said, limit how much black or green tea you drink. You can also purchase certain water filters that remove some fluoride. There’s no reason to stop brushing your teeth with fluoride toothpaste — just don’t swallow it.
