Does fluoride exposure in pregnancy affect childhood IQ?

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While water fluoridation has great benefits for tooth decay prevention, research indicates that in pregnant women, fluoride crosses the placenta and accumulates in brain regions involved in learning and memory. A new study in JAMA Pediatrics explored how maternal fluoride exposure during pregnancy impacts childhood IQ.

The prospective, multicenter birth cohort study used information from the Maternal-Infant Research on Environmental Chemicals (MIREC) program, which recruited pregnant women from 10 cities across Canada. The sample included mother-child pairs and children were between ages 3 and 4 at the time of testing. Forty-one percent of the participants lived in communities supplied with fluoridated municipal water.

The authors used maternal urinary fluoride (MUF_SG), adjusted for specific gravity and averaged across each trimester of pregnancy. Water treatment plants measured fluoride levels daily if fluoride was added to municipal drinking water and weekly or monthly it was not added. Participants’ postal codes were matched with water treatment plant zones to provide an estimate of water fluoride concentration for each woman. Participants also self-reported daily fluoride intake from water and beverage consumption.

Among the 512 mother-child pairs included in the study, mean (SD) age for enrollment for mothers was 32.3 (5.1) years. The majority (90%) of participants were white and 264 children (52%) were female. Data on MUF_SG concentrations, IQ scores and complete covariates were available for al mother-child pairs, but self-reported data on maternal fluoride intake and children’s IQ were available for 400 pairs.

Women who lived in areas with fluoridated tap water (n=141) had significantly higher mean MUF_SG  (SD) concentrations than women in areas with non-fluoridated tap water (n=228) (0.69 [0.42] mg/L vs 0.40 [0.27] mg/L; P =.001, respectively) and fluoride intake levels (0.93 [0.43] vs 0.30 [0.26] mg of fluoride per day; P =.001, respectively). 

Children had mean (SD) Full Scale IQ scores of 107.16 (13.26), range 52-143. Girls in the study (109.56 [11.96]) had significantly higher mean (SD) scores than boys (104.61 [14.09). The authors also noted a significant interaction (P = .02) between child sex and MUF_SG (6.89; 95% CI 0.96 – 12.82) and they believe this indicated a differential association between boys and girls.

Results from the study indicated that in boys, as maternal fluoride levels increased, IQ levels decreased.  Fluoride levels are significantly associated with a lower IQ in boys, but this relationship was not evident in girls. A 1-mg/L increase in MUF_SG was associated with a 4.49-point lower IQ score (95% CI -8.38 to -.060) in boys and no significant association with IQ scores among girls (B = 2.40; 95% CI -2.53 to 7.33). However, 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) for both boys and girls.

The authors believe that this study indicates that maternal exposure to higher levels of fluoride during pregnancy are associated with lower IQ scores in children aged 3 to 4. Ob/gyns treating patients in areas with fluoridated water may want to consult expectant mothers about reducing their fluoride intake during pregnancy, but given that these are new findings, more research is needed to clarify their significance.