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Study: Fluoride in Water May Lower Your Kid’s IQ

A new study found that fluoridated water may have impact preschool intelligence. Before you turn off the tap, hear the experts out.

Fluoridated water may adversely impact the intelligence of kids in the womb according to a recent study published in the Journal of American Medical Association Pediatrics. The findings are likely to renew the debate around the safety of the fluoridation of municipal water supplies. But no one is concluding that parents or kids should avoid tap water.

“I wouldn’t change anything based on this data,” says John P.A. Ioannidis Professor in Disease Prevention in the School of Medicine at Stanford, who was not involved in the study. “It’s a fair effort based on what data is available, but it’s far from perfect and the signal is weak.”

The study, titled “Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada,” analyzed the IQ outcomes of children from 601 child-mother pairs. Of the mothers, all of whom gave birth in Canada between 2008 and 2012, 41 percent lived in communities with a fluoridated water supply. The IQ assessments occurred when the children were 3 and 4 years old and statistical analysis was used to find associations between IQ and fluoridation exposure in the womb.  

The findings from the analysis revealed that exposure to fluoridated water in pregnancy was associated with a 1 to 4 point decrease in preschool IQ scores. However, at lower levels, fluoride exposure appeared to affect boys’ IQ scores only, with no effect on girls. Higher levels of exposure were associated with a 3 point decrease in both boys’ and girls’ IQ scores. 

Importantly, the study does not conclude the lower preschool IQ scores are caused by fluoride exposure in pregnancy, but rather that the two are associated. Likewise, the sample size is relatively small to draw much larger conclusions. 

In their note, the editors of the JAMA admitted that the decision to publish the study was difficult. They also note the findings were subject to additional scrutiny but published in the interest of child safety rather than controversial findings. 

“Scientific inquiry is an iterative process,” the editors write. “It is rare that a single study provides definitive evidence.”

Ioannidis agrees, characterizing the study as an “interesting observation that was worthwhile publishing.” After all, he suggests, there are mountains of evidence that speak to the public health benefits of fluoridation programs, compared to the hints of fluoridation dangers. 

It’s worth noting that three-quarters of America’s municipal water supply is fluoridated. And many communities have been fluoridating their water since the 1950s. Ioannidis notes that if there were a very strong risk of neurotoxicity related to intelligence it would have surfaced by now. He notes that poor dental hygiene and bad teeth could also lower IQ.

Ioannidis cautions parents when making choices based on scientific studies. “Sometimes science is pursuing questions that are likely one in a million to be true,” he says. “Take a deep breath and move on.”