88. Critical windows of fluoride neurotoxicity in Canadian children (lay summary)

Farmus L, Till C, Green R, Hornung R, Martinez-Mier EA, Ayotte P, Muckle G, Lanphear BP, Flora DB. Environmental Research 2021 May 26:111315. doi: 10.1016/j.envres.2021.111315. Online ahead of print

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 been associated with lowered IQ in young children.  Scientists don’t know if fluoride exposure during pregnancy has a different effect on IQ than exposure during infancy or early childhood. To answer this question, researchers at York University investigated the effect of fluoride, measured at three different time points, on children’s IQ.

Using data on 596 mothers and children from the Mirec pregnancy cohort, researchers measured fluoride exposure during pregnancy, infancy, and in childhood.  Children’s IQ was measured using a test of cognitive ability called the Wechsler Preschool and Primary Scale of Intelligence-III.  This test measures Verbal, Performance, and Full scale IQ scores based on an assessment of, for example, vocabulary and information processing.  Children were between 3 to 4 years old when IQ was measured. Researchers determined the association between fluoride exposure at different time points and children’s IQ using statistical models.

Higher fluoride exposure, at all time points, tended to be associated with slightly lower – about 2 to 3 points – Performance IQ scores.  This association was strongest when using the prenatal measure of fluoride exposure.  Researchers observed that the associations were different between boys and girls. Among boys, the prenatal window appeared critical, while for girls, infancy was critical.

This study demonstrates that the association between fluoride exposure and Performance IQ differed depending on the timing of exposure.  This study also found differences between boys and girls. Further research on how the association between fluoride exposure, at different time points, and IQ differs between boys and girls will help confirm these findings.