Objectives: To investigate the association of exposure to per- and polyfluoroalkyl substances (PFAS) during early pregnancy with markers of the maternal thyroid system. Methods: Serum concentrations of seven PFAS as well as thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4), free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study. Outcomes were concentrations of TSH and thyroid hormones, FT4/FT3 or TT4/TT3 ratios, TSH/FT4 ratio as a marker of the negative feedback loop, TT4/FT4 or TT3/FT3 ratios as markers of the binding of thyroid hormones to binding proteins. Results: The study population comprised 2,008 women with median (95% range) gestational age of 10 (6–14) weeks. There was no association between PFAS and TSH. Higher PFNA, PFDA, PFHpA and PFOA levels were associated with a higher FT4 (largest effect estimate for PFDA: β [95% CI]: 0.27 [0.10 to 0.45], P = 0.002). Higher PFUnDA levels, but no other PFAS, were associated with a lower FT3 (β [95% CI]: −0.05 [-0.09 to −0.01], P = 0.005). Higher PFUnDA levels were associated with lower TT4 (β [95% CI]: −1.58 [-3.07 to −0.09]) and there was an inverted U-shaped association of PFOS with TT4 (P = 0.03). Higher PFDA, PFUnDA, PFHpA levels were associated with a lower TT3. Overall, higher PFAS concentrations were associated with a higher FT4/FT3 ratio and a higher TT4/TT3 ratio. There was no association of PFAS with the TSH/FT4 ratio. Higher concentrations of several PFAS were associated with lower TT4/FT4 and TT3/FT3 ratios. Conclusions: These findings translate results from experimental studies suggesting that exposure to PFAS may interfere with the thyroid system during pregnancy. Further experimental studies should take into account human evidence to better understand the potential underlying mechanisms of thyroid disruption by PFAS exposure.
Bibliographical noteFunding Information:
We are grateful to biomedical laboratory technicians Agneta Kristensen, Margareta Maxe, and Åsa Amilon at the Division of Occupational and Environmental Medicine at Lund University, Sweden, for performing the analyses of PFAS and cotinine.
This project has been supported by the Exchange in Endocrinology Expertise (3E) program of the European Union of Medical Specialists (UEMS), Section and Board of Endocrinology and the ATHENA project, funded under the European Union’s Horizon 2020 Programme for research, technological development and demonstration, grant agreement no. 825161. The SELMA study was funded by grants from the Swedish Research Council (Formas). The sample analyses were supported by Region Skåne and the Medical Faculty at Lund University, Sweden.
© 2022 The Authors