Association between maternal fluoride exposure during pregnancy and IQ scores

Green R, Lanphear B, Hornung R, et al. e in Offspring in Canada. JAMA Pediatr. Published online August 19, 2019. doi:10.1001/jamapediatrics.2019.1729

Key points

Question  Is maternal fluoride exposure during pregnancy associated with childhood IQ in a Canadian cohort receiving optimally fluoridated water?

Findings  In this prospective birth cohort study, fluoride exposure during pregnancy was associated with lower IQ scores in children aged 3 to 4 years.

Meaning  Fluoride exposure during pregnancy may be associated with adverse effects on child intellectual development, indicating the possible need to reduce fluoride intake during pregnancy.

Abstract

Importance  The potential neurotoxicity associated with exposure to fluoride, which has generated controversy about community water fluoridation, remains unclear.

Objective  To examine the association between fluoride exposure during pregnancy and IQ scores in a prospective birth cohort.

Design, Setting, and Participants  This prospective, multicenter birth cohort study used information from the Maternal-Infant Research on Environmental Chemicals cohort. Children were born between 2008 and 2012; 41% lived in communities supplied with fluoridated municipal water. The study sample included 601 mother-child pairs recruited from 6 major cities in Canada; children were between ages 3 and 4 years at testing. Data were analyzed between March 2017 and January 2019.

Exposures  Maternal urinary fluoride (MUFSG), adjusted for specific gravity and averaged across 3 trimesters available for 512 pregnant women, as well as self-reported maternal daily fluoride intake from water and beverage consumption available for 400 pregnant women.

Main Outcomes and Measures  Children’s IQ was assessed at ages 3 to 4 years using the Wechsler Primary and Preschool Scale of Intelligence-III. Multiple linear regression analyses were used to examine covariate-adjusted associations between each fluoride exposure measure and IQ score.

Results  Of 512 mother-child pairs, the mean (SD) age for enrollment for mothers was 32.3 (5.1) years, 463 (90%) were white, and 264 children (52%) were female. Data on MUFSG concentrations, IQ scores, and complete covariates were available for 512 mother-child pairs; data on maternal fluoride intake and children’s IQ were available for 400 of 601 mother-child pairs. Women living in areas with fluoridated tap water (n = 141) compared with nonfluoridated water (n = 228) had significantly higher mean (SD) MUFSG concentrations (0.69 [0.42] mg/L vs 0.40 [0.27] mg/L; P = .001; to convert to millimoles per liter, multiply by 0.05263) and fluoride intake levels (0.93 [0.43] vs 0.30 [0.26] mg of fluoride per day; P = .001). Children had mean (SD) Full Scale IQ scores of 107.16 (13.26), range 52-143, with girls showing significantly higher mean (SD) scores than boys: 109.56 (11.96) vs 104.61 (14.09); P = .001. There was a significant interaction (P = .02) between child sex and MUFSG (6.89; 95% CI, 0.96-12.82) indicating a differential association between boys and girls. A 1-mg/L increase in MUFSG was associated with a 4.49-point lower IQ score (95% CI, −8.38 to −0.60) in boys, but there was no statistically significant association with IQ scores in girls (B = 2.40; 95% CI, −2.53 to 7.33). A 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score (95% CI, −7.16 to −0.14) in boys and girls.

Conclusions and Relevance  In this study, maternal exposure to higher levels of fluoride during pregnancy was associated with lower IQ scores in children aged 3 to 4 years. These findings indicate the possible need to reduce fluoride intake during pregnancy.

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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.”…

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.”… 

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…

Before publication, the study was subjected to two statistical reviews, with the researchers combing through the data to make sure that the results were not skewed by the mothers’ education, income levels, or other factors.

The findings were astonishing to JAMA editors, who had been told throughout their medical training that fluoridation was completely safe and that opponents were wingnuts relying on “junk science.”…

The CDC declined to discuss the study, saying it does not comment on outside research.  The American Academy of Pediatrics said it is looking forward to future studies “to see if they demonstrate the same results or provide more conclusive evidence.” The American College of Obstetricians and Gynecologists, which recommends that pregnant women use fluoridated toothpaste and mouth rinses, isn’t making any changes for now….

Sophia Lubin, an OB-GYN in Brooklyn, New York, said she’s never had a patient ask her about fluoridated water, but expects she will be questioned about it now.

“As an obstetrician, you always have to think about two people—the mother and the baby,” she said. ”And oral health is important for mothers.”

She anticipates telling women that if they are truly concerned, they can switch to bottled water during pregnancy. But she doesn’t think, at this point, that she will tell patients they should not drink from the tap.

One part of the study that struck her was how much fluoride is in black tea, which soaks it up from soil. She said she is more likely to tell patients to cut back on tea than on water, since it’s important they stay hydrated.

“This left me with a lot more questions than answers,” Lubin said…

The study authors noted a number of limitations, the most significant of which is that they did not assess how much fluoride the children were exposed to after birth.

Dr. Stuart Ritchie, a neuroscientist at King’s College London, called the finding “pretty weak.”

“They might be interesting as part of a larger set of studies on this question, but alone they shouldn’t move the needle much at all on the question of the safety of fluoride,” he wrote.

But in an analysis that accompanied the study, Harvard Professor David Bellinger said that while “high-quality epidemiological studies” are needed, “the hypothesis that fluoride is a neurodevelopmental toxicant must now be given serious consideration.”

Those kinds of studies take time—which doesn’t help millions of parents-to-be who may be looking for advice now.

“The question that needs to be asked to every pediatrician, scientist, and epidemiologist is what they’re going to tell pregnant women,” said Christakis, who says he will advise his pregnant friends and family to avoid fluoridated water.

“We can’t tell them to wait years for another study. They have to decide what to tell their patients now.”

https://www.thedailybeast.com/fluoridated-water-during-pregnancy-linked-to-lower-iqs-study-published-by-jama-pediatrics-says