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The prevalence of autism spectrum disorder has risen in recent decades. Given the growing evidence that prenatal fluoride exposure may be neurotoxic, we examined associations between prenatal fluoride exposure and parent-reported autistic behaviors in preschool-aged children. We studied 453 mother-child pairs using data from the Maternal-Infant Research on Environmental Chemicals (MIREC) study, a prospective Canadian birth cohort. Autistic behaviors were assessed in children at 3 to 4 years using the Social Responsiveness Scale-Second Edition (SRS-2) Preschool Form, where a higher score indicates more autistic behaviors. We estimated prenatal fluoride exposure using three methods: (i) maternal urinary fluoride adjusted for specific gravity (MUFSG), from spot urine samples collected at each trimester and the mean calculated across samples, (ii) daily maternal fluoride intake, based on self-reported consumption of tap water, coffee, and tea during the first and third trimesters, and (iii) water fluoride concentration in tap water. We used multivariable linear regression models to estimate associations between the SRS-2 scale T-scores and each fluoride exposure separately. We used multivariable logistic regression to estimate the association between each prenatal fluoride exposure and an elevated SRS-2 total T-score (i.e., 90th percentile or higher). Potential effect modification of MUFSG was examined by child sex, daily folic acid supplementation, and plasma total folate in pregnancy. The mean SRS-2 total T-score for children aged 3 to 4 years was 45.3 (SD = 6.1, range = 34 to 85). The median MUFSG concentration was 0.43 mg/L (interquartile range = 0.33 mg/L). MUFSG was not significantly associated with the SRS-2 total T-score in multivariable linear regression (β = -0.16; 95% CI, -1.70, 1.39) or logistic regression (OR = 0.76; 95% CI, 0.29, 1.96). Similarly, estimated daily fluoride intake and water fluoride concentration were not associated with the SRS-2 total T-score. No effect modification was observed. There was no evidence of an association between prenatal fluoride exposure and autistic behaviors in preschool-aged children, in contrast to previous MIREC research findings on lead and phthalates. Given that this cohort has relatively few children with high SRS-2 scores, further research is needed in other groups of children to more fully explore this association.
Carty et al. (Tue,) studied this question.