Maternal Fluoride Exposure and Offspring IQ: An Investigation of the Potential Mediating Role of Thyroid Dysfunction in Pregnancy

Objective: Fluoride exposure has been associated with thyroid dysfunction; however, no studies to date have examined whether fluoride disrupts thyroid function in pregnant women. We evaluated the potential thyroid-disrupting effects of fluoride exposure in pregnancy and tested whether thyroid disruption in pregnancy would mediate the association between maternal fluoride exposure and child IQ in Canadian mother-child dyads.

Methods: Maternal thyroid dysfunction was estimated using both categorical measures of thyroid health status (i.e., euthyroid, subclinical, and primary hypothyroid) and continuous measures of thyroid hormone levels (i.e., TSH, FT4, and TT4).

Results: We observed a statistically significant association between water fluoride concentration and greater risk of primary hypothyroidism, and between primary hypothyroidism in pregnancy and lower IQ among male offspring. Further, higher urinary fluoride concentration was associated with higher TSH among women pregnant with female, but not male fetuses. Maternal thyroid hormone levels were not associated with offspring IQ.

Conclusion: Results suggest that maternal thyroid dysfunction in pregnancy may be one mechanism underlying the association between fluoride exposure in pregnancy and offspring IQ.