Exposure to Polybrominated Diphenyl Ethers (PBDEs) and Hypothyroidism in Canadian Women

Context: Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide range of products, resulting in widespread human exposure. Epidemiological studies in some populations reported exposure to PBDEs and thyroid hormone levels but little epidemiological data are available among women from the general population. Objective: The objective of the study was to examine the association of PBDEs with hypothyroidism. Design and Setting: This was a cross-sectional analysis of the 2007–2009 Canadian Health Measures Survey. Participants: A total of 745 women representative of Canadian women aged 30–79 years participated in the study. Main Outcome and Methods: We estimated the prevalence ratios (PRs) for hypothyroidism in relation to plasma concentrations of BDE-47, -99, -100, and -153 and their sum (ΣPBDEs). Women were identified as cases if they reported a doctor-diagnosed thyroid condition and underwent thyroid hormone replacement therapy (n = 90). Results: Higher plasma levels of brominated diphenyl ether (BDE)-47 and -100 and ΣPBDEs were associated with an increased prevalence of hypothyroidism. The PR for a 10-fold increase in ΣPBDEs was 1.7 (95% confidence interval [CI] 1.0, 3.0). Associations were consistently higher among women aged 30–50 years than among those 51–79 years for ΣPBDEs and the other PBDE congeners, although the interaction was significant only for BDE-100. For instance, in the younger age group, women with detectable levels of BDE-100 had a PR of 3.8 (95% CI 1.2, 12.3) compared with women with undetectable levels; the corresponding PR in the older age group was 1.2 (95% CI 0.6, 2.3). No association was observed for BDE-99 and -153. Conclusion: Plasma PBDE levels were associated with an increased prevalence of hypothyroidism in Canadian women aged 30–50 years. Although the cross-sectional design of the study limits inferences of causality, these findings have important implications, given the key role of thyroid hormones in several biological mechanisms during reproductive age.