Fluoride Exposure During Pregnancy Linked With Lower IQ Scores in Children

Exposure to higher levels of fluoride during pregnancy may be associated with adverse effects on child intellectual development, according to findings of a study published this week in JAMA Pediatrics.

Researchers examined maternal fluoride exposure during pregnancy and associations with childhood IQ in a Canadian cohort receiving optimally fluoridated water. Water fluoridation is supplied to approximately 66% of US residents, 38% of Canadian residents, and 3% of European residents to prevent tooth decay. Community water fluoridation has become increasingly controversial due to potential neurotoxicity associated with fluoride exposure, but these links have remained unclear.

Laboratory studies have shown that when fluoride crosses the placenta, it accumulates in brain regions involved in learning and memory, subsequently altering proteins and neurotransmitters in the central nervous system.

The prospective birth cohort study used information from the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort to analyze children born between 2008 and 2012. The study sample included 601 mother-child pairs recruited from 6 major cities in Canada:

• Maternal urinary fluoride (MUF_SG) available for 512 pregnant women
• Self-reported maternal daily fluoride intake from water and beverage consumption available for 400 pregnant women
• Children’s IQ assessed at ages 3 to 4 years using the Wechsler Primary and Preschool Scale of Intelligence-III
• The median MUF_SG concentration was 0.41 mg/L.

Of 512 mother-child pairs, 463 (90%) were white, with the mean (SD) age for enrollment of mothers being 32.3 years. The study revealed a significantly higher mean (SD) MUF_SG concentration in women living in areas with fluoridated tap water (n = 141; 0.69 [0.41] mg/L; P = .001) compared with nonfluoridated water (n = 228; 0.40 [0.27] mg/L; P = .001). There was a significant interaction (P = .02) between child sex and MUF_SG (6.89; 95% CI, 0.96-12.82) indicating a differential association between boys and girls, which was further shown by significantly higher mean (SD) IQ scores found in girls (109.56 [11.96] versus boys (104.61 [14.09]; P = .001).

A 1-mg increase in MUF_SG 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 found in girls. While girls have exhibited an overall higher tolerance to MUF_SG concentrations, 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 both boys and girls.

“To our knowledge, this study is the first to estimate fluoride exposure in a large birth cohort receiving optimally fluoridated water,” said the authors. “Collectively, these findings support that fluoride exposure during pregnancy may be associated with neurocognitive effects.”

While the study shows a significant correlation between heightened fluoride exposure and lower IQ scores in children, further studies are necessary to assess its impact on different races/ethnicities and associated learning disabilities such as attention-deficit/hyperactivity disorder. The significance of antenatal exposure as opposed to infant exposure is also an issue that researchers are currently investigating.

“Our future analyses will assess exposure to fluoride in the MIREC cohort in infancy and early childhood,” said the authors.

Reference

Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada [published online August 19, 2019]. JAMA Pediatrics. doi: 10.1001/jamapediatrics.2019.1729.