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. 2021 Sep:200:111315.
doi: 10.1016/j.envres.2021.111315. Epub 2021 May 27.

Critical windows of fluoride neurotoxicity in Canadian children

Linda Farmus  1 , Christine Till  2 , Rivka Green  1 , Richard Hornung  3 , E Angeles Martinez Mier  4 , Pierre Ayotte  5 , Gina Muckle  6 , Bruce P Lanphear  7 , David B Flora  1
Affiliations

Critical windows of fluoride neurotoxicity in Canadian children

Linda Farmus et al. Environ Res. 2021 Sep.

Erratum in

Abstract

Background: Fluoride has been associated with IQ deficits during early brain development, but the period in which children are most sensitive is unknown.

Objective: We assessed effects of fluoride on IQ scores across prenatal and postnatal exposure windows.

Methods: We used repeated exposures from 596 mother-child pairs in the Maternal-Infant Research on Environmental Chemicals pregnancy and birth cohort. Fluoride was measured in urine (mg/L) collected from women during pregnancy and in their children between 1.9 and 4.4 years; urinary fluoride was adjusted for specific gravity. We estimated infant fluoride exposure (mg/day) using water fluoride concentration and duration of formula-feeding over the first year of life. Intelligence was assessed at 3-4 years using the Wechsler Preschool and Primary Scale of Intelligence-III. We used generalized estimating equations to examine the associations between fluoride exposures and IQ, adjusting for covariates. We report results based on standardized exposures given their varying units of measurement.

Results: The association between fluoride and performance IQ (PIQ) significantly differed across prenatal, infancy, and childhood exposure windows collapsing across child sex (p = .001). The strongest association between fluoride and PIQ was during the prenatal window, B = -2.36, 95% CI: -3.63, -1.08; the association was also significant during infancy, B = -2.11, 95% CI: -3.45, -0.76, but weaker in childhood, B = -1.51, 95% CI: -2.90, -0.12. Within sex, the association between fluoride and PIQ significantly differed across the three exposure windows (boys: p = .01; girls: p = .01); among boys, the strongest association was during the prenatal window, B = -3.01, 95% CI: -4.60, -1.42, whereas among girls, the strongest association was during infancy, B = -2.71, 95% CI: -4.59, -0.83. Full-scale IQ estimates were weaker than PIQ estimates for every window. Fluoride was not significantly associated with Verbal IQ across any exposure window.

Conclusion: Associations between fluoride exposure and PIQ differed based on timing of exposure. The prenatal window may be critical for boys, whereas infancy may be a critical window for girls.

Keywords: community water fluoridation; critical windows of exposure; fluoride neurotoxicity; generalized estimating equations; intelligence quotient.

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Conflict of interest statement

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1.
Fig. 1.
Flowchart of mother-child dyads with neurodevelopmental testing. Note. MUF = maternal urinary fluoride; IFI = infant fluoride intake; CUF = child urinary fluoride.
Fig. 2.
Fig. 2.
Standardized associations between fluoride exposure windows and IQ outcomes using GEE. Note. Dots represent point estimates and tails represent 95% confidence intervals.
See this image and copyright information in PMC

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