Prenatal fluoride exposure may be linked to long-term lower general cognitive levels, specifically deficits in nonverbal IQ or visual-spatial and perceptual reasoning abilities, according to a study published March 9 in Environmental Research.
Fluoride exposure was associated significantly with nonverbal and verbal IQ losses in kids ages 6 to 12, according to researchers from U.S., Canada, and Mexico. However, there was a greater link to performance or nonverbal IQ shortfalls than to verbal IQ deficits in preschoolers with higher prenatal fluoride exposure.
"These findings contribute to the growing body of evidence on fluoride's neurotoxicity and indicate a need to develop recommendations for pregnant women," wrote the authors, led by Martha Téllez-Rojo, PhD, of the National Institute of Public Health, Cuernavaca, Morelos, Mexico.
Past studies have reported positive associations between fluoride from dietary sources, including drinking water and salt, and urinary fluoride levels in pregnant women. This is due to fluoride's ubiquity and its ability to pass through the placenta and blood-brain barrier to reach the fetal brain.
In August 2019, these same researchers published a study in the 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.
In the current study, researchers investigated data on fluoride exposure and IQ scores from 328 pairs of mothers and children from the Early Life Exposures in Mexico to Environmental Toxicants (Element) cohort. The participants live in a region of Mexico in which fluoride is added to salt.
Researchers measured the average maternal urinary fluoride (MUF) concentration at pregnancy trimesters while adjusting for creatinine. They used generalized estimating equation (GEE) models to estimate the population averaged effect of MUF concentration on longitudinal general cognitive index (GCI)/full-scale IQ (FSIQ), verbal IQ (VIQ), and performance IQ (PIQ) scores. The IQs of children ages 4 and 5 and from 6 to 12 were examined, according to the study.
After reviewing the data, a significant negative relationship was found between maternal urine fluoride concentration and full-scale IQ and performance IQ at ages 4 and 5, they wrote. However, the mother's fluoride concentration was not linked significantly to lower verbal IQ scores, the authors wrote.
|Decrease in IQ points for kids for every 0.5 mg/L increase of MUF concentrations|
|Age||Full-scale IQ||Performance IQ||Verbal IQ|
|4 years||-2.12||-3.08||Not significant|
|5 years||-1.97||-2.46||Not significant|
|6 to 12 years||-2.01||-1.80||-1.93|
At ages 6 to 12 years, a dramatic negative association between maternal urine fluoride concentration and all three IQ outcomes was found, they wrote.
The study's limitations included that maternal nonfasting spot urine samples were used to estimate fluoride exposure. Urinary fluoride has a short half-life of about five hours, and drinking fluoride-free water before a urine test can dilute a sample.
Future studies should examine prenatal fluoride exposure using biomarkers that capture more chronic exposure to fluoride, including fingernail or toenail clippings or baby teeth, they noted. In addition, further research should be conducted to explore the mechanism of action of low-level fluoride exposure that prioritizes the difference between verbal and nonverbal intelligence, Tellez-Rojo and colleagues wrote.
"In conclusion, prenatal exposure to fluoride is associated with sustained impacts on IQ," they wrote.