Thyroid Function and Plasma Concentrations of Polyhalogenated Compounds in Inuit Adults

Abstract

BackgroundSeveral ubiquitous polyhalogenated compounds (PHCs) have been shown to alter thyroid function in animal and in vitro studies. So far, epidemiologic studies have focused on the potential effect of a small number of them, namely, polychlorinated biphenyls (PCBs) and some organochlorines (OCs), without paying attention to other important PHCs.ObjectivesWe investigated the relationship between exposure to several PHCs and thyroid hormone homeostasis in Inuit adults from Nunavik.MethodsWe measured thyroid parameters [thyroid-stimulating-hormone (TSH), free thyroxine (fT4), total triiodothyronine (tT3), and thyroxine-binding globulin (TBG)] and concentrations of 41 contaminants, including PCBs and their metabolites, organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorooctanesulfonate (PFOS), and a measure of dioxin-like compounds, detected in plasma samples from Inuit adults (n = 623).ResultsWe found negative associations between tT3 concentrations and levels of 14 PCBs, 7 hydroxylated PCBs (HO-PCBs), all methylsulfonyl metabolites of PCBs (MeSO2-PCBs), and 2 OCPs. Moreover, we found negative associations between fT4 levels and hexachlorobenzene Concentrations. TBG concentrations were inversely related to 8 PCBs, 5 HO-PCBs, and 3 OCPs. Exposure to BDE-47 was positively related to tT 3, whereas PFOS concentrations were negatively associated with TSH, tT3, and TBG and positively with fT4 concentrations.ConclusionExposure to several PHCs was associated with modifications of the thyroid parameters in adult Inuit, mainly by reducing tT3 and TBG circulating concentrations. The effects of PFOS and BDE-47 on thyroid homeostasis require further investigation because other human populations display similar or higher concentrations of these chemicals.