Research that fluoride affects kids' IQs may be flawed

A 2019 study that suggested fluoride negatively affects children's IQ scores and has been cited to sabotage public water fluoridation is "unacceptable" for legal and policy purposes. The commentary was published on March 25 in Community Dentistry and Oral Epidemiology.

Research, including the 2019 Canadian study, published based on the Canadian Maternal-Infant Research on Environmental Chemicals (MIREC) study database, fails to offer valid fluoride and IQ measurements, which means the claims that community water fluoridation may be linked with harm to fetal and infant cognitive development cannot be supported, the authors wrote.

"The MIREC database offers neither valid data on maternal or foetal fluoride exposure, nor reliable measures of the IQ of the resulting children, the database cannot be used to make claims that fluoride exposure affects IQ," wrote the authors, led by Dr. Juliet Guichon of the Cumming School of Medicine at the University of Calgary in Canada.

In August 2019, a study was published in JAMA Pediatrics that suggested maternal exposure to greater levels of fluoride during pregnancy was linked with lower IQ scores in children ages 3 to 4 in six major Canadian cities. The study included data on fluoride exposure and IQ scores from 512 pairs of mothers and children in which about 40% lived in areas with a fluoridated water supply. The water was fluoridated at or below the recommended level.

The most recent analysis showed that 2019 study and any others that based their data on the MIREC database are flawed because the researchers reported a fluoride-IQ association after they estimated fluoride levels of the pregnant women using spot urine samples collected during pregnancy. Spot samples of urinary fluoride cannot accurately measure a person's exposure to fluoride, the authors wrote.

Additionally, the way children's IQs were measured was unreliable. Administrators used different IQ tests in each Canadian city, they wrote.

However, the authors noted that they did not conduct a formal quality assessment of these articles because they did not complete a systematic review. Instead, the goal of this commentary was to explore the severe limitations that the MIREC fluoride-IQ authors failed to address in their research, Guichon et al wrote.

Due to these findings, the American Fluoridation Society is urging JAMA Pediatrics to consider retracting the paper, according to a press release dated March 25 from the organization.

"The flawed assessment of exposure to fluoride is insurmountable," the authors wrote.