An influential medical journal published a study Monday that links fluoride consumption during pregnancy with lower childhood IQs—a finding that could undermine decades of public-health messaging, fire up conspiracy theorists, and alarm mothers-to-be.
The research was expected to be so controversial that JAMA Pediatrics included an editor’s note saying the decision to publish it was not easy and that it was subjected to “additional scrutiny.”
“It is the only editor’s note I’ve ever written,” Dimitri Christakis, editor in chief of JAMA Pediatrics and a pediatrician, told The Daily Beast. “There was concern on the journal’s editorial team about how this would play out in the public eye and what the public-health implications would be.”
About three-fourths of the United States drinks fluoridated tap water—which the U.S. Centers for Disease Control and Prevention declared one of the 10 greatest public-health achievements of the 20th century because it dramatically reduces tooth decay.
A handful of earlier studies have suggested that prenatal fluoride exposure could affect neurodevelopment, but many experts considered those to be substandard.
The new study, vetted by the premier medical publisher in the U.S., is seen as more rigorous, although some experts found it unconvincing, saying the results were statistically borderline and the methodology was flawed.
“When we started in this field, we were told that fluoride is safe and effective in pregnancy,” said study co-author Christine Till of York University in Toronto. “But when we looked for the evidence to suggest that it’s safe, we didn’t find any studies done on pregnant women.”
They recruited 512 pregnant women from six Canadian cities and measured their exposure several ways: analyzing the amount of fluoride in their urine; looking at how much tap water and tea they drank; and comparing the fluoride concentration in the community drinking water.
Then, when the women’s children were 3 or 4, the researchers gave them IQ tests and crunched the numbers to see if they could find any trends.
“We saw an association between prenatal fluoride exposure and lower IQ scores in children,” study author Rivky Green said.
Specifically, they found a 1 mg per liter increase in concentration of fluoride in urine was associated with a 4.5 point decrease in IQ among boys—though not girls. Another translation: The boys of mothers with the most fluoride in the urine had IQs about 3 points lower than the boys of mothers with the least amount.
Although critics of the study pointed to the different results by gender as a red flag, when the researchers measured fluoride exposure by examining the women’s fluid intake, they found lower IQs in boys and girls. A 1 mg increase per day was associated with a 3.7-point IQ deficit among both.
While medical organizations are not advising that pregnant women avoid fluoridated water—and the study has no implications for the use of fluoride after birth—Green believes the results are significant enough to warrant a change in behavior.
“What we recommend is lowering fluoride ingestion during pregnancy,” she said.