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Fluoride Exposure During Pregnancy Linked to Lower IQ in Sons

The authors of the study that found the association say more research is needed on maternal fluoride and child IQ.

Aug 20, 2019
Ashley P. Taylor

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A study published yesterday (August 19) in JAMA Pediatrics reports an association between a pregnant mother’s urinary concentration of fluoride, often added to drinking water as a public health measure to reduce cavities, and the IQ of her son, but not her daughter, at age 3 or 4.

Fluoride prevents cavities by strengthening tooth enamel, and fluoridation of drinking water has been widely adopted in the US. Yet research has revealed potential risks associated with fluoride exposure during pregnancy. A small 2017 study conducted in Mexico, for example, has already suggested a link between prenatal fluoride exposure and IQ.

Using data collected as part of the Maternal-Infant Research on Environmental Chemicals program on pregnant mothers and their children born between 2008 and 2012 in six Canadian cities, the researchers examined the effects of mothers’ fluoride exposure during pregnancy and the IQ of their children at age 3 or 4. About 40 percent of expecting mothers in the study came from cities with fluoridated water. These pregnant mothers had average urinary fluoride levels of 0.69 milligrams per liter, compared with 0.4 milligrams per liter for women living in cities without fluoridated water. After controlling for potential confounding variables, the researchers found that a 1-milligram-per-liter increase in a mother’s urinary fluoride levels was associated with an approximately 4.5-point lower IQ score in her son.

However, there was no association between mothers’ urinary fluoride levels and their daughters’ IQ scores.

Study author Rivka Green, a neuropsychology doctoral candidate at York University in Toronto, Canada, tells Science that she hopes the study will prompt further research. “We tried to be as cautious and careful as possible,” she says. “We’re not coming in saying that fluoride is poison or anything like that. We’re just . . . letting the data tell the story.”

David Bellinger, a professor of neurology at Harvard Medical School and Boston Children’s Hospital who was not involved in the study, agrees. “Generally, no single epidemiological study settles a question like this,” he tells The Washington Post. Bellinger reviewed the paper and also wrote an editorial about it.

Until more information is available on the risks of fluoride exposure during pregnancy, study coauthor Christine Till of York University, tells NPR, “[w]e recommend that women reduce their fluoride intake during pregnancy.” 

Ashley P. Taylor is a New York–based freelance reporter. Follow her on Twitter @crenshawseeds and read her work at ashleyptaylor.com.

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