91. A Benchmark Dose Analysis for Maternal Pregnancy Urine-Fluoride and IQ in Children (lay summary)

Grandjean P, Hu H, Till C, Green R, Bashash M, Flora DB, Tellez-Rojo MM, Song P X.K, Lanphear BP, Budtz-Jørgensen E. Risk Analysis 2021 Jun 8. doi: 10.1111/risa.13767

Fluoride is a mineral found naturally in most water sources. About one-third of Canadians have fluoride added to their public water supply to protect teeth from decay.  While fluoride at low concentrations can improve oral health, there are concerns about the health effects of fluoride exposure particularly in young children.  High levels of fluoride have, for example, been associated with lowered IQ in young children.  Researchers from Harvard University, York University, University of Southern California, and the University of Copenhagen undertook this study to determine the fluoride concentration that would lead to a one point decrease in children’s IQ. This concentration is called a “benchmark dose” or “benchmark concentration”.

Researchers pooled results from two recent birth cohort studies: Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) study in Mexico and the MIREC study in Canada. Fluoride was measured in urine from pregnant women in both studies. The ELEMENT study measured children’s IQ at age 4 and again between ages 6 to 12.  The MIREC study measured children’s IQ between ages 3 to 4. Researchers used statistical models to determine the concentration of maternal fluoride in urine that is linked to a one point decrease in IQ.

The benchmark concentration of maternal urinary fluoride that corresponded to a one point decrease in IQ was 0.31 mg/L in preschool aged children from both cohorts.  The concentration was similar (0.33 mg/L) when considering older children.

Results from this study can be used to guide regulatory decisions on how to prevent excess fluoride exposure among pregnant women.