2020 - Hypothyroidism in Pregnancy - Fluoride - Canada

All adverse health effects of fluoride are related to thyroid hormone metabolism.
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2020 - Hypothyroidism in Pregnancy - Fluoride - Canada

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Green R, Farmus L, Lanphear B, Martinez-Mier E, Flora D, Ayotte P, Till C - "Water fluoride levels and hypothyroidism in a Canadian pregnancy cohort" Abstract in: Neurotoxicol Teratol 79:106885 (2020) doi: 10.1016/j.ntt.2020.106885. Epub 2020 Apr 13. PMID: 32298771; PMCID: PMC7252070
Held in conjunction with the 60th Annual Meeting of the Society for Birth Defects Research and Prevention and the 33rd Annual Education Meeting for the Organization of Teratology Information Specialists, Charleston, South Carolina, June 27-July 1, 2020: Meeting Cancelled due to COVID-19 Global Pandemic.


Fluoride has been reported to disrupt thyroid function, but the risk of hypothyroidism in pregnant women exposed to fluoride has not been rigorously studied. The objective was to test the association between fluoride exposure and hypothyroidism in Canadian pregnant women enrolled in the Maternal-Infant Research on Environmental Chemicals cohort. Using a cross-sectional design, we compared women who reported a diagnosis of clinical hypothyroidism or reported taking medication for hypothyroidism (n = 51) against non-hypothyroid controls (n = 1276). We measured fluoride concentrations in urine, drinking water, and fluoride intake based on women's self-reported beverage consumption during pregnancy. We used logistic regression to assess the association between fluoride exposure and hypothyroid status, controlling for covariates. A 1 mg/L increase in water fluoride levels was associated with a 3.88 (95% CI: 1.27, 12.51) increased odds of having hypothyroidism. Similarly, a 1 mg increase in fluoride intake per day was associated with a 2.01 (95% CI: 1.22, 3.26) increased odds of having hypothyroidism. Urinary fluoride was not significantly associated with hypothyroidism (OR = 1.19, 95% CI: 0.81, 2.19). Higher exposure to fluoride from drinking water may increase risk of hypothyroidism in pregnant women. It could be that water fluoride, a stable measure of lifelong fluoride exposure, predicted hypothyroidism, as opposed to urinary fluoride. Future studies are needed to confirm these findings with measures of thyroid hormones.
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