Study linking mother's fluoride exposure to lower IQ scores in kids raises questions

Young children whose mothers consumed higher levels of fluoride while pregnant scored slightly lower on IQ scores than their peers, according to a new study.

The study, published Monday in JAMA Pediatrics, used two measures to evaluate the amount of fluoride that women in six Canadian cities consumed during pregnancy. When their children ages 3 and 4 were given cognitive tests, researchers reported a small drop in IQ scores among kids whose moms had higher levels of fluoride exposure when pregnant.

Still, experts not involved in the limited observational study say that one research paper should not change public policy on the widespread use of community fluoridated water, long a subject that has stirred public debate.

For one, the study’s design could not rule out other factors that might affect cognitive scores.

The peer-reviewed journal's editor, Dimitri Christakis, acknowledged the controversial nature of the study in an editor's note that accompanied the study. In the note, Christakis said the study was subject to extra scrutiny for its methods and findings.

"This study is neither the first, nor will it be the last, to test the association between prenatal fluoride exposure and cognitive development," Christakis wrote in the editor's note. "We hope that purveyors and consumers of these findings are mindful of that as the implications of this study are debated in the public arena."

Brittany Seymour, a Harvard School of Dental Medicine assistant professor of public policy, said more research is needed to determine the possible health effects, if any, of prenatal exposure to fluoride.

"We always want to be cautious and take our time to allow additional peer review," Seymour, an American Dental Association spokesperson, told USA TODAY. "Can these findings be replicated to find out if they have any weight?"

Most U.S. residents get fluoridated tap water from public water systems. The Centers for Disease Control and Prevention described community water fluoridation as one of the top 10 public health achievements of the 20th century for reducing cavities and improving oral health.

More than one-third of Canadian residents get fluoridated tap water, while a small percentage of European residents do.

Christine Till, an associate professor at York University and the study’s senior author, said her research team's goal was to provide new data on the effects of prenatal exposure to fluoridated water. She noted her team's study followed a 2017 study in Mexico that also linked prenatal exposure to lower IQ scores.

"It is our hope that our findings – and all the other studies that are done – are used to inform policy," Till said. "The question now becomes how will the policymakers weight the risks and benefits,” of fluoride in public water systems.

Till's research team examined women and children in six of Canada's largest cities: Vancouver, Montreal, Kingston, Toronto, Hamilton and Halifax. The children lived in communities within those metro regions that either had or did not have fluoridated water systems.

Researchers used two measures of fluoride exposure: Urine samples collected as part of a previous research project and self-reports of tap water, black tea or coffee the women consumed while pregnant.

The research team obtained the frozen urine samples from the Maternal-Infant Research on Environmental Chemicals, a Canadian study that examined births from 2008 to 2012.

Among the 512 women who provided three urine samples during pregnancy, researchers said a 1 milligram-per-liter increase in fluoride in the mother’s urine was associated with a 4.5-point drop in IQ tests among boys, but not girls.

The other test evaluated self-reported data from 400 mothers who drank fluoridated tap water, black tea or coffee. Among mothers in that group, the study found a 1 milligram-per-liter increase in fluoride intake was associated with a 3.7-point decrease in IQ scores among boys and girls.

In an accompanying editorial, Boston Children’s Hospital researcher David Bellinger noted that the study raises questions such as whether boys face greater risk than girls or if prenatal period is the most critical window of exposure. The study does not address how fluoride might affect children after birth.

"Therefore, these studies do not provide any guidance regarding the management of children’s postnatal exposures to fluoride, such as the age at which fluoride toothpaste should be introduced and the quantity that should be applied to a child’s brush at different ages," Bellinger said.

Still, despite the study's limitations, Bellinger said that researchers must give "serious consideration" to the hypothesis that fluoride might be a neurodevelopmental toxicant, and that more research is needed to conclude whether there are any public health implications.

This article originally appeared on USA TODAY: Fluoride exposure in pregnancy linked to children's IQ scores