New Study Links In Utero Fluoride Exposure to Neurobehavioral Issues in 3-Year-Olds

The study found that children were about 1.8 times more likely to show behavioral problems for every additional 0.68 mg/L of fluoride they were exposed to in utero.

Kaitlin Sullivan, Medscape, May 21, 2024

Exposure to fluoride during gestation is linked to neurobehavioral issues in children by age 3 years, a new study in JAMA Network Open found.

The research adds to a growing body of observational studies conducted in North America showing a link between exposure to fluoride and childhood IQ, neurotoxicity, and brain development.

Based on the evidence thus far, "we suggest that it is warranted for pregnant individuals to drink filtered tap water," said Tracy Bastain, PhD, an associate professor of clinical population and public health sciences at the University of Southern California Keck School of Medicine in Los Angeles and a co-author of the research.

Studies have shown that fluoride can cross the placenta and blood-brain barrier, Bastian said.

The latest work included 229 mother-child pairs primarily living in Los Angeles who are part of a larger dataset comprising primarily low-income Latino families.

Bastain and her colleagues analyzed fluoride levels in urine samples taken from pregnant women between 2017 and 2020 and neurobehavioral data of their children 3 years later. The parents completed a 99-question evaluation of various behaviors by their children that could indicate neurobehavioral problems, including attention-deficit/hyperactivity disorder and anxiety.

The average concentration of fluoride in urine for women in the study was 0.76 mg/L (0.51-1.19) , which is on-par with levels among pregnant women in North America who are exposed to fluoridated water, which is common in the United States and Canada, or fluoridated salt, which is common in Mexico, according to Ashley Malin, PhD, an assistant professor in the Department of Epidemiology at the University of Florida College of Public Health and Health Professions and the UF College of Medicine in Gainesville and a co-author of the research.

No clear standards exist for safe levels of fluoride in urine. About three quarters of Americans drink fluoridated drinking water. Guidelines from the US Food and Drug Administration indicate that fluoride levels = 0.7 mg/L in water are safe.

The team found that children were about 1.8 times more likely to show behavioral problems for every additional 0.68 mg/L of fluoride they were exposed to in utero. About one third of the 90 children who exhibited behavioral problems had a combination of internalized problems - such as anxiety or, in more extreme cases, refusing to speak - and externalized issues, such as rule-breaking or aggression.

The results "raise questions about the impact fluoride has on the brain of a developing baby," said Malin.

Some research has found that fluoride disrupts thyroid hormones, which are critical for brain development.

Malin said that she and her colleagues did not evaluate drinking water habits among participants, so they cannot say how women consumed the chemical.

However, rice - which absorbs fluoride present in tap water - was a food staple among many of the families. Green and black teas also contain high amounts of fluoride because the leaves absorb the chemical as they grow.

"What we still need to know now is if the level of fluoride we are adding to drinking water in the U.S. and in Canada is safe, or if it needs to be lowered or eliminated completely," said Deborah Dewey, PhD, a professor in the Department of Pediatrics and Community Health Sciences at the University of Calgary in Alberta, Canada.

Dewey added that research has shown that higher levels of fluoride cause problems with fetal brain development among residents of Iran and China, where water naturally contains high amounts of fluoride. However, these findings cannot be extrapolated to a North American population, where fluoride exposure is generally lower.

"These levels of fluoride that have been recommended by health agencies for fluoridation of water for prevention of dental cavities may not be the appropriate level for impact on brain development," Dewey said.

After Canadian and Mexican studies published in 2017 and 2019, the American College of Obstetricians and Gynecologists (ACOG) said that it still supported pregnant women consuming fluoridated water due to its dental benefits.

The group "does not have a position on fluoride in pregnancy, including fluoridated water. Our clinical experts will certainly review and consider this study, but we do not have a position at the time," wrote Kate Connors, ACOG director of communications and public affairs, in an email.

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